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Element-specific magnetic moments of epitaxially grown Fe3Si in D03 crystal symmetry were analyzed by means of x-ray absorption spectroscopy and its associated magnetic circular dichroism. To detect the weak magnetization induced at the Si sites, measurements were performed at both the Si K edge and the Si L3,2 edges. By band structure calculations based on either the SPR-KKR method or FLAPW with GGA, the spectroscopic features could be reproduced and provide an insight to the underlying physics. In addition, comparison of the experimental data to calculated spectra made it possible for us to estimate the induced effective spin and orbital magnetic moment of Si in our sample, i.e., μseff=(−0.011±0.005) μB and μl=(−0.003±0.003) μB, respectively. The sign and the order of magnitude of the tiny orbital magnetic moment has been confirmed by application of the magneto-optical sum rule.
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PHYSICAL REVIEW B 85, 214432 (2012)
Induced magnetism on silicon in Fe3Si quasi-Heusler compound
C. Antoniak,1H. C. Herper,1Y. N. Zhang,2A. Warland,1T. Kachel,3F. Stromberg,1B. Krumme,1C. Weis,1K. Fauth,4
W. Keune,1P. Entel,1R. Q. Wu,2J. Lindner,1and H. Wende1
1Fak ul t ¨
at f¨
ur Physik and Center for Nanointegration Duisburg-Essen (CeNIDE), Universit¨
at Duisburg-Essen,
Lotharstr. 1, 47048 Duisburg, Germany
2Department of Physics and Astronomy, University of California, Irvine, California 92697, USA
3Helmholtz-Zentrum Berlin f¨
ur Materialien und Energie – Speicherring BESSYII, Albert-Einstein-Str. 15, 12489 Berlin, Germany
4Experimentelle Physik IV, Universit¨
at W¨
urzburg, Am Hubland, 97074 W¨
urzburg, Germany
(Received 6 October 2010; published 26 June 2012)
Element-specific magnetic moments of epitaxially grown Fe3Si in D03crystal symmetry were analyzed by
means of x-ray absorption spectroscopy and its associated magnetic circular dichroism. To detect the weak
magnetization induced at the Si sites, measurements were performed at both the Si Kedge and the Si L3,2edges.
By band structure calculations based on either the SPR-KKR method or FLAPW with GGA, the spectroscopic
features could be reproduced and provide an insight to the underlying physics. In addition, comparison of
the experimental data to calculated spectra made it possible for us to estimate the induced effective spin and
orbital magnetic moment of Si in our sample, i.e., μeff
s=(0.011 ±0.005) μBand μl=(0.003 ±0.003) μB,
respectively. The sign and the order of magnitude of the tiny orbital magnetic moment has been confirmed by
application of the magneto-optical sum rule.
DOI: 10.1103/PhysRevB.85.214432 PACS number(s): 75.50.Bb, 78.70.Dm
In spintronics or magnetoelectronics, the intrinsic spin of an
electron and its associated magnetic moment is used as a carrier
for information in addition to its electronic charge. Compared
to devices based on conventional charge transport, spintronic
devices offer the possibility to realize fast processing at low
power costs. The spin-polarized current needed in this case can
be generated by passing the current through a ferromagnetic
electrode. In order to combine this new field of electronics with
the established semiconductor technologies, spin injection
from the ferromagnet into a semiconductor is essential and has
already been extensively investigated.13The Fe3Si compound
on GaAs has turned out to be a promising candidate of
ferromagnet/semiconductor systems with its spin injection
efficiency of above 2% at a temperature of 150 K and 1%
at room temperature.4
Fe3Si is a quasi-Heusler compound that crystallizes in the
D03symmetry in the chemically ordered phase with a lattice
constant a=5.65 ˚
A. As depicted in Fig. 1,Featomsare
located at two inequivalent lattice sites (A and B), and Si
occupies the lattice site C. While Fe-A atoms are surrounded
by four Fe and four Si nearest neighbor atoms, Fe-B atoms
are surrounded by eight Fe nearest neighbor atoms. Random
occupancies of sites B and C, or all three sites, lead to a
B2 (CsCl)-like or A2 (bcc) symmetry, respectively. Due to
the different neighborhood in the D03structure, Fe-A and
Fe-B atoms have different magnetic moments, namely 1.2 μB
and 2.4 μBas obtained from neutron diffraction experiments.5
The structure of Fe3Si can be represented by the long-range
ordering parameters S(B2) and S(D03) which are defined by
the occupation probabilities Piof Fe at the different lattice
sites i=A, B by the following equations:6
S(B2) =1
PA(1 x)
x(1 x)(1)
2PA+PB3(1 x)
x(1 x),(2)
where xdenotes the Si content, i.e., x=0.25 in the case of
Fe3Si. A perfect D03structure is described by S(D03)=1 and
S(B2) =2/3, respectively. When grown onto a semiconductor
like GaAs, the actual crystal symmetry should be strongly dis-
turbed by interfacial diffusion7which influences the electronic
and magnetic properties as well.8To avoid diffusion of Ga
and/or As atoms into the metal, a tunnel-barrier spin-injector
was used in this work, i.e., Fe3Si was grown on 3 nm MgO
on GaAs(001). For this case, the magnetic properties can be
well controlled at the interface, which is more stable even at
elevated temperatures than direct ferromagnet/semiconductor
heterostructures. In addition, increasing the interface resis-
tance by a MgO tunnel barrier helps to reduce the large
impedance mismatch9that prevents efficient spin injection
across the interface.
A lot of effort has been made over the last decades to
characterize Fe3Si compounds in terms of phase stability,
structure, electronic and magnetic properties.10,11 However,
its static and dynamic magnetization behavior is strongly
dominated by Fe due to its large magnetic moment with
respect to Si and three times larger amount. Therefore, a direct
measurement of the weak magnetization of Si—necessary for
the complete understanding of the magnetic properties of the
compound—has remained a challenge for years. In this paper,
we focus on the induced magnetism on Si: By measuring
the x-ray absorption near-edge structure (XANES) and x-ray
magnetic circular dichroism (XMCD) not only at the Fe L3,2
absorption edges, but also at the Si L3,2and Si K edges, a clear
evidence of a magnetic signal from Si was found. By com-
parison with spectra obtained from band structure calculations
using the Korringa-Kohn-Rostoker (KKR) method on the one
hand and the full potential linearized augmented planewave
(FLAPW) approach on the other hand, we reached quantitative
understanding of structural and magnetic properties.
The organization of the paper is as follows: In
Sec. II,M
ossbauer spectroscopy is introduced to structurally
1098-0121/2012/85(21)/214432(8) ©2012 American Physical Society
C. ANTONIAK et al. PHYSICAL REVIEW B 85, 214432 (2012)
FIG. 1. (Color online) Schematic B2-like and D03structure of
characterize the Fe3Si system by extracting the long-range
ordering parameters S(D03) and S(B2), respectively, before
we turn to the XANES and XMCD measurements. In Sec. III
we present the details of band structure calculations using the
two methods mentioned above. The induced magnetism of Si
in Fe3Si is discussed in Sec. IV by comparison of experimental
and calculated spectra before conclusions are given in the last
A. Performance and sample characterization
To preserve the chemical ordering, a tunnel-barrier spin-
injector was used in this work. After growing 3 nm MgO on
cleaned GaAs(001) with a (4 ×6) surface reconstruction, two
samples of 8 nm Fe3Si were prepared by coevaporation of Fe
and Si in a UHV chamber with a base pressure of 108Pa.
They were grown at a substrate temperature of 250 C with
deposition rates of 0.064 ˚
A/sof57Fe and 0.036 ˚
Si, respectively. One sample was subsequently annealed at
500 C before capping with 3 nm MgO to prevent oxidation of
the Fe3Si film. Conversion electron M¨
ossbauer spectroscopy
(CEMS) at perpendicular incidence of the γrays onto the film
surface was employed to investigate the degree of D03order
of the two samples.
The experimental CEMS data can be fitted by the procedure
described by Arita et al.,6yielding the long-range ordering
parameters S(D03) and S(B2). The samples prepared here
obviously display a high degree of chemical and structural
order as can be seen from the M¨
ossbauer results shown in
Fig. 2. For the nonannealed sample we found S(D03)=0.86
and S(B2) =0.53, respectively. Annealing of the sample leads
to an even higher degree of chemical order as indicated by the
ordering parameters S(D03)=0.88, S(B2) =0.55.
X-ray absorption measurements were performed at the PM-
3 bending magnet beamline at the HZB-BESSY II synchrotron
radiation facility in Berlin/Germany at T=14 K in magnetic
fields of μ0Hext 1 T in total electron yield (TEY) mode
by measuring the sample drain current. The SX700-type
plane grating monochromator (PGM) offers the possibility
to measure at variable degree of circular polarization σin the
energy range between 20 eV and about 2000 eV with an energy
resolution in the order of 103–104. Here, the photon energy
was varied between 90 eV E130 eV around the Si L3,2
absorption edges, 680 eV E790 eV around the Fe L3,2
edges, and 1820 eV E1960 eV around the Si K edge.
For all cases, the fixed focus constant was set to the standard
value cff =2.25. With the specific settings actually used in
our experiment, the absolute values of energy resolution were
FIG. 2. (Color online) Conversion electron M¨
ossbauer data of
nonannealed (upper panel) and annealed (lower panel) Fe3Si at room
temperature and fitted spectra with the extracted long-range ordering
parameters S(D03) and S(B2). Note that a perfect D03symmetry is
represented by S(D03)=1andS(B2)=2/3.
estimated to be 15 meV at 100 eV and 1.24 eV at 1850 eV,
In order to optimize the experimental figure of merit—
containing σ2times the photon flux—different out-of-plane
(vertical) angles of the emitted x-rays with respect to the
storage ring plane had to be used for the various photon
energies. The different resulting values of σwere calculated
for the energy of Si L3,2,SiK,andFeL
3absorption edges using
the well-known equations for the emission characteristics of
the radiation.12 At the Fe L3edge the calculated values were
checked by measuring the asymmetry of an Fe bulk sample
for different monochromator settings, i.e., for x-rays emitted
under different vertical angles. For the actual settings used we
found σ=92.5% for measurements at the Fe L3,2absorption
edges, σ=76.5% at the Si K edge, and σ=88.0% at the Si
L3,2absorption edges.
After each scan, either the magnetic field or the photon
helicity was reversed. Field-dependent magnetization curves
were measured at the photon energy of 710 eV at the Fe L3
edge normalized to the pre-edge signal at 700 eV and at the
Si K edge at a photon energy of 1851 eV normalized to the
pre-edge signal at 1841 eV.
For XANES and XMCD data analysis, a linear background
was subtracted from the experimental data. In the case of Fe,
electron excitations into the final 3dstates were separated from
the ones into higher states or the continuum by a two steplike
function necessary for the determination of spin and orbital
magnetic moments by a standard sum rule-based analysis.1315
Since this procedure fails in the case of Si due to its broad p
band, spin and orbital magnetic moments of Si were estimated
by comparison to calculated spectra. Only the sign and the
order of magnitude could reliably be estimated by application
of the sum rule for XMCD at the K edge.16,17 The intra-atomic
dipole term μtthat is included in the experimentally obtained
effective spin magnetic moment μeff
s=μs+7μtis assumed
to be negligible in the cubic Fe3Si system investigated in this
FIG. 3. (Color online) X-ray absorption near-edge structure and circular dichroism at Si L3,2,FeL
3,2, and Si K absorption edges of annealed
Fe3Si measured at T=14 K under normal x-ray incidence. The external magnetic field was applied parallel to the x-ray beam.
work. However, since μtis probably not vanishing completely,
the spin magnetic moments derived from experimental data are
denoted effective spin magnetic moment.
B. Results
Experimental x-ray absorption spectra of Fe and Si in
Fe3Si are shown in Fig. 3. In the case of Fe, the spectra are
already corrected for self-absorption and saturation effects18
assuming an electron escape depth of λe=2nm.Similartothe
CEMS data, no significant difference between the annealed and
nonannealed sample is observed. Thus, we focus here on the
annealed sample which exhibits a slightly improved chemical
ordering. At the Fe L3,2absorption edges, the spectral shape
of XANES and its associated XMCD indicate an Fe-d/Si-sp
hybridization of Fe on lattice sites A (cf. Fig. 6) as discussed
in the literature on the basis of calculated spin and angular
momentum resolved density of states.8
In the case of Si, the L3and L2edges are not energetically
well separated. There are six spectral features visible in the
XANES shown in Fig. 3. Four of them, aL,bL,cL, and dL,arise
from Si in Fe3Si as will be revealed later by comparison with
calculated spectra. (The index Lis related to the absorption
edge.) The small pre-edge peak at 95 eV can be assigned
to Mg of the MgO cap layer. An additional shoulder in the
experimental XANES above bL(around 107 eV) may be an
indication for a Si-rich interface to the MgO cap layer since Si
tends to segregate at the surface of Fe-Si alloys. The XMCD
signal at the Si L3,2absorption edges shows a maximum
asymmetry of only about 0.8% and is enlarged by a factor of
10 in Fig. 3for clarity. In order to ensure the reliability of the
XMCD signal, not only pairs of spectra with reversed sample
magnetization but also with different polarization of x-rays
were analyzed. Interestingly, a meaningful XMCD can only
be found around 104 eV, the position of the peak bL. Compared
to the Fe signal at the L3absorption edge, the reversed sign
of the XMCD at the Si sites already suggests an antiparallel
alignment of Fe and Si spins.
The XMCD at the K edge is sensitive only to the orbital
magnetic contribution which is known to be very small.
Nevertheless, in our experiment a clear magnetic signal was
measured with a maximum XMCD asymmetry of about 0.3%.
Although this value of asymmetry is extremely small, we were
able to directly measure the field-dependent magnetization by
detecting the absorption signal at the energy position of the
maximum XMCD signal, i.e., 1851 eV, while sweeping the
external magnetic field.19 The signal was normalized to the pre-
edge signal at 1841 eV. Equivalent measurements were per-
formed at the Fe L3edge at photon energies of 710 and 700 eV,
respectively. The results are shown in Fig. 4. Although it is
almost at the detection limit, it can clearly be seen that the
field dependence of the Si XMCD follows the one measured
at the Fe sites. A magnetic hysteresis could not be measured
since the superconducting magnet used in this experiment is
not well suited to resolve small coercive fields.
A. Computational details
In order to provide insight for the explanation of experi-
mental data, the XANES and XMCD spectra of bulk Fe3Si
were calculated using density functional approaches. The
optical absorption tensor was calculated by means of the linear
response formula proposed by Wang and Callaway.20 While
the calculated XANES and XMCD spectra at the Fe L3,2
absorption edges match well the measured data,8the reliability
of calculations at the Si edges is unclear due to the delocalized
nature of its 3pstates. In particular, the influence of muffin
tin (MT) approximation on the quality of spectra is not known
at the present. Here we use two different methods, namely
the spin polarized relativistic KKR (SPR-KKR) technique21
FIG. 4. (Color online) Element-specific field dependent magne-
tization measured by means of XMCD at the Fe L3edge (710 eV)
and Si K edge (1851 eV), respectively.
C. ANTONIAK et al. PHYSICAL REVIEW B 85, 214432 (2012)
and the full-potential linear augmented plane wave (FLAPW)
method, for the determination of magnetic properties of
Fe3Si. Using these two methods also gives the possibility
to ensure that the results do not significantly depend on the
approximations made in the electronic structure calculations,
namely the atomic sphere approximation (ASA) or non-fully-
relativistic treatment.
Within the SPR-KKR method the electronic structure is
represented in terms of Green’s functions evaluated by means
of the multiple scattering theory. The ASA is adopted and the
interstitial region is eliminated by using overlapping spheres.
In contrast, the FLAPW is viewed as the most precise approach
with no shape approximation in the entire space for wave
function, charge density, and potential.22,23 The core electrons
were described fully-relativistic, while the valence electrons
are treated in a scalar-relativistic manner, and the spin-orbit
coupling term for the valence states was invoked second
variationally.24 In both SPR-KKR and FLAPW calculations
we used the generalized gradient approximation (GGA) in
the parametrization of Perdew, Burke, and Ernzerhof25,26
to describe the exchange correlation interaction. The lattice
constant of the D03unit cell was chosen based on experi-
mental data, a=5.65 ˚
A. Integrations over the Brillouin zone
(BZ) were evaluated over a 20 ×20 ×20 k-point grid. The
convergence against energy cutoffs and the maximum angular
momentum lmax were carefully monitored. In the SPR-KKR
calculations lmax =3 was used for the calculation of the spec-
tra, whereas lmax =8 was used in the FLAPW calculations.
B. Results
The magnetic moments obtained from the ab initio calcula-
tions are summarized in Table I. Obviously the spin moments
μsat the Fe sites are overestimated by both methods. It
has been noted in many theoretical studies2729 that for the
transition metals, in particular the 3dmetals, the GGA always
produce larger lattice parameters and smaller bulk moduli
compared with the local spin density approximation (LSDA)
results. It was also pointed out by Singh and Ashkenazi30 that
in GGA there is an increased tendency towards magnetism in
general, and particularly towards larger magnetic energies for
magnetic materials, which in other cases may just result in a
small quantitative error. Furthermore, discrepancies between
the magnetic moments obtained from FLAPW and SPR-KKR
are mainly dedicated to the choice of the Wigner Seitz sphere
used for the projection to the lattice.
XANES and XMCD spectra at the Si L3,2and K edges as
well as the Fe L3,2edges calculated by means of SPR-KKR and
FLAPW method, respectively, are shown in Fig. 5. The nicely
reproduced main features of the experimental XANES and
XMCD indicate the validity of our computational approaches
TABLE I. Site-specific spin and orbital magnetic moments of Fe
and Si in Fe3Si calculated by SPR-KKR and FLAPW.
Fe A sites Fe B sites Si C sites
μs[μB] 1.39 1.33 2.67 2.55 0.121 0.062
μl[μB] 0.030 0.020 0.054 0.051 0.0019 0.0004
and parametrizations. The D03structure assumed in our cal-
culations should be rather dominant in the measured samples.
As evidence for the insignificance of ASA, the spectroscopic
profiles obtained from the SPR-KKR and FLAPW methods
closely follow each other in the entire energy range. This can
be understood since the x-ray spectra depend on the overlap
between valence and atomic-like core states. The two peaks at
95 and 107 eV arise from the MgO buffer layer and possible
deviations from the Fe3Si composition at the film surface and
hence are missing in the theoretical data. As in the experiment,
the Si L3,2XANES spectrum exhibit an onset peak at the
photon energy of about 97 eV followed by three pronounced
peaks at 104, 110, and 121 eV denoted as aL,bL,cL, and dLas
in Fig. 3. The XMCD spectrum only shows an intense positive
peak at bLin good accordance with the experimental data. The
amplitudes of the XMCD at the Si absorption edges appears
to be very weak at both the L3,2and K edges (less than 1% of
the XANES). This indicates that the induced spin and orbital
magnetic moments on Si are small (cf. Table I).
Since both XANES and XMCD signals are related to the
dipole transitions from the inner-shell states to the unoccupied
valence states,31,32 it is useful to analyze the density of states
(DOS) above the Fermi level EF. Here, the partial DOS curves
of Fe3Si obtained from the FLAPW are presented in Fig. 6.
As discussed in the literature,8,33 the two types of Fe atoms
have different electronic properties, and the Fe-A atoms have
a strong effect on the DOS profiles of Si atoms. Interestingly,
there are two pronounced peaks in the Si s-DOS curves at about
5 eV above EF, slightly split in two spin channels. They reflect
the hybridization between the t2gorbitals of Fe-A atoms and
the Si sstates. Via intra-atomic hybridization, this feature can
also be found in the dDOS and result in the peaks in the Si L3,2
XMCD curves at 104 eV. (For an easier assignment, this region
is denoted as bin the DOS since it is related to the spectral
features of XANES and XMCD denoted bL,bKin Fig. 5.)
The K edge involves electronic excitations from the 1score
states towards the pconduction states. These states mediate
the magnetization in Fe3Si and are the main ingredients in the
valence and conduction bands of this alloy. Figure 6shows that
the contribution to the positive onset at the Si K edge XMCD is
ascribed to the pstate above EFin the majority spin channel.
The pronounced resonant peaks for Si, Fe-A, and Fe-B atoms
in 1–2 eV (denoted a) are responsible for the large negative
peak of the XMCD spectra at the Si K edge (denoted aK).
The results of XANES and XMCD spectra plotted in
Fig. 7display that the density functional calculations using
the perfect D03structure reproduce very well the experimental
data, in particular the XMCD. It is well known3335 that XMCD
spectra of dia- or paramagnetic elements with induced ferro-
magnetism in an alloy can be utilized to characterize atomic
arrangements since their spectroscopic features are highly
sensitive to the change in interactions with ferromagnetic
species. It is reasonable to conclude that the Fe3Si films used in
the experiment consist mainly of D03symmetry. In addition,
the good agreement between theory and experiment in the
XMCD features indicates the possibility of determining tiny
magnetic moments in complex compounds.
FIG. 5. (Color online) Calculated XANES and XMCD spectra at the Si L3,2,Fe
3,2and Si K edges by means of SPR-KKR (upper panel)
and FLAPW (lower panel), respectively.
Taking a closer look at the XANES and XMCD signals, the
agreement of the Si XANES is less satisfactory compared to
the XMCD. Since we only considered the initial state effect
in the optical transition, we do not attempt to go much beyond
the comparison on peak positions. Furthermore, the FLAPW
method produced more fine structures in the higher energy
range compared to the SPR-KKR results. This discrepancy
can be assigned to the fact that the SPR-KKR method uses
Wigner-Seitz partition for the whole space, thus eliminating
the interstitial region from the formalism.27,36
The effective spin and orbital magnetic moments at the Fe
sites were determined by a sum-rule based analysis of the
FIG. 6. (Color online) The spin and orbital resolved density of
states of Fe3Si. Positive and negative sides are for the spin-up and
spin-down parts, respectively. The amplitude for Si s-, p-, and d-states
are rescaled by a factor of 10.
XMCD and are listed in Table II. Note that it is impossible
to distinguish between the moments of Fe on lattice sites A
and B through analyzing the absorption spectra at the L3,2
edges since the differences in energy position and spectral
shape are marginal. The averaged Fe moment is significantly
smaller than in bulk α-Fe and in good agreement to values
reported earlier.8For a better comparison with our calculations,
the magnetic moments obtained from theory were also site
averaged and listed in Table II.
The intrinsic and instrumental broadening of the experi-
mental spectra yield a strong overlap of the L3and L2edges
of Si. Also the FLAPW calculation shows that the energy
separation between 2p1/2and 2p3/2states is only 0.6 eV. Thus,
a straight-forward determination of spin and orbital magnetic
moments by integral methods is impossible.37 Nevertheless,
the good agreement between theory and experiment allows
us to access this information from theory with confidence. To
better appreciate the quality of our results, the experimental
Si XMCD signal at both L3,2and K edges are rescaled and
compared in Fig. 7. The magnetic moments in our sample can
be estimated by comparing the scaling factors of XANES and
XMCD. This procedure is commonly used for experimental
data for which the standard sum-rule based analysis fails.
At the Si K edge, the experimental XANES was scaled
by a constant factor to fit the intensity of the corresponding
spectrum calculated by the SPR-KKR method in the pre-
and post-edge region. Note that the spectra shown in Fig. 7
correspond to the absorption cross-section in units of Mb
(1 b =1028 m2) and no longer in arbitrary units. However,
scaling the XMCD with the same factor is not sufficient
to achieve good agreement between experimentally and
theoretically obtained dichroism. At the Si L3,2edges, the
experimental XMCD spectrum had to be enlarged by a factor
C. ANTONIAK et al. PHYSICAL REVIEW B 85, 214432 (2012)
FIG. 7. (Color online) Experimentally obtained and calculated XANES and XMCD at the Si L3,2absorption edges and the Si K edge,
respectively. The experimental data were normalized to fit the calculated XANES intensity in the pre- and post-edge region. To fit the intensity
of the calculated dichroism, experimental XMCD data have been scaled by an additional factor that is used for an estimation of the magnetic
moments of Si in the Fe3Si sample.
of about 6 in order to coincide with the calculated one. Since
the major contribution to the XMCD asymmetry arises from
the spin magnetic moment in this case, it can be concluded
that the spin magnetic moment at the Si atoms in our sample
is roughly eight times smaller than the theoretically expected
value, i.e., μeff
s=(0.011 ±0.005) μB. At the Si K edge,
the experimental XMCD signal is sensitive only to the orbital
magnetic moment and has to be scaled down by a factor of
0.4 to be in good agreement with the calculated spectrum.
Consequently, the orbital magnetic moment in our sample is
about twice as large as the theoretically expected value, i.e.,
μl=(0.003 ±0.003) μB. The large error bar arises not only
from the low signal-to-noise ratio of the experimental data, but
also from the difference in calculated magnetic moments by
TABLE II. Site-averaged (effective) spin and orbital magnetic
moments of Fe and Si in Fe3Si determined by XMCD and band
structure calculations by two different approaches. Note that the
effective spin magnetic moment μeff
sextracted from experimental
data is denoted μsfor an easier reading of the table.
Fe μs[μB]μl[μB]
experiment 1.76 ±0.10 0.073 ±0.01
KKR 1.82 0.038
FLAPW 1.73 0.030
Si μs[μB]μl[μB]
experiment 0.011 ±0.005 0.003 ±0.003
KKR 0.121 0.0019
FLAPW 0.062 0.0004
the two different methods, although the amplitude of XMCD
is roughly the same.
For the sake of completeness, the magneto-optical sum rule
has been applied to the data obtained at the Si K edges as
presented below. However, since the energy cutoff for the
integral and hence the number of pholes are not well defined
for the itinerant pstates, one should keep in mind that the
validity of this analysis is questionable in our case. Following
the magneto-optical sum rule for the K edge as derived by
Igarashi and Hirai,16,17 the orbital magnetic moment can be
calculated according to
where μc=μ+μis the XMCD signal and μ0=μ++
μis the so-called white line intensity of the XANES.
The latter is shown in Fig. 8after subtraction of a steplike
background together with the integrals of the white line and
XMCD respectively are shown in Fig. 8for the experimental
data and the spectra calculated by the SPR-KKR method.
Using a rough estimation for the number of unoccupied p
states, np
h=3, we obtain for the calculated spectra an orbital
magnetic moment of about μl≈−0.0015 μBin agreement
with the value obtained directly by this calculation. However,
it can be seen in Fig. 8that the value depends on the cutoff
energy for the integrals. For the case of the experimental
data, the value of μldepends even stronger on the cutoff
energy. The strong oscillations of the XMCD signal and,
consequently, in the integral of the XMCD may be related to
the magnetic counterpart of the extended x-ray absorption fine
FIG. 8. (Color online) XANES after subtraction of steplike back-
ground for experimental data (gray line) and SPR-KKR calculation
(red line), respectively, and their integrals (top). Integral of XMCD
signal of experimental data and SPR-KKR calculation (bottom).
structure (MEXAFS). While the extended x-ray absorption
fine structure (EXAFS) is an interference effect between the
outgoing photoelectron as a matter wave and backscattered
waves from neighboring atoms, MEXAFS includes a spin
dependence of the scattering events.37 In our case, the Si
atoms are surrounded by Fe atoms with a quite large magnetic
moment. Thus, the MEXAFS is expected to give a quite large
contribution to our magnetic signal with respect to the small
XMCD of Si with its tiny magnetic moment, and the integral
value of the Si XMCD can only be estimated. Here, we
choose the value by averaging the signal above 1862 eV as
depicted by a horizontal line in Fig. 8. With this method the
orbital magnetic moment amounts to μl≈−0.003μBwhich
is in agreement with the value presented above obtained by
scaling the experimental data to fit the calculated spectra.
Although the absolute value from the sum-rule-based analysis
is ambiguous, the negative sign of μlcan be confirmed. In
addition, it is obvious that the integral of the XMCD (Fig. 8),
and consequently the orbital magnetic moment, is larger in the
experiment than in the SPR-KKR calculation.
In the following, we turn to the discussion of some reasons
for the different spin and orbital magnetic moments in theory
and experiment. The spin magnetic moments at the Si sites
may be reduced by a nonperfect surface of the Fe3Si film: As
already mentioned above, the shoulder in the XANES above
the Si L3,2absorption edge may indicate a segregation of Si
at the Fe3Si surface which likely occurs in Fe-Si alloys and
alters the composition ratio and atomic structure. This is
reported in the literature,38 where the cubic FeSi (c-FeSi)
was found to influence the spectral shape of photoemission
spectra39 of Fe3Si a few eV above the main absorption
edge similar to our experimental findings. In addition, the
measurements presented in this work are surface sensitive.
Especially at low photon energies, the x-ray attenuation length
in the MgO cap layer and the Fe3Si is reduced to about 10 nm.40
Therefore, even a thin Si-enriched layer at the surface of Fe3Si
may strongly affect the XANES. However, the contribution of
c-FeSi or other Fe-Si compounds to the XMCD is negligible
since they do not exhibit any ferromagnetic order. Thus, the Si
atoms near the surface will not measurably contribute to the
XMCD asymmetry if the composition significantly deviates
in this region. The XMCD signal compared to the XANES
intensity would be reduced as a consequence. Note that a
difference in the intensities of the double-peak structure for
annealed and nonannealed samples could not be obtained. The
annealing appears not to change the composition along the
depth if we follow the arguments above.
At higher photon energies, e.g., at the Si K edge, the
measurement is less surface sensitive and the contribution of
the bulk of Fe3Si to the total signal is larger. However, the
TEY detection mode of XANES and XMCD still leads to
an emphasis of the signal arising from surface atoms due to
self-absorption effects. Therefore, it is also reasonable to scale
experimental XANES and XMCD with different factors for
comparison to theory.
From computational aspects, there is also a distinct uncer-
tainty in the amplitude of XANES because of the exclusion
of final state effects as mentioned before. Better quality of
comparison for the XMCD spectra is due to cancellation of
this effect yielding different scaling factors for XANES and
XMCD to match experimental data. In addition, it seems to
be a general trend in such alloys, that theory underestimates
the orbital contributions to the total magnetic moments and
often overestimates spin moments whereby the overestimation
of the spin moments is produced by the GGA and the small
orbital moments are related to correlation effects. All these
effects discussed here are reflected in the large error bars of
the magnetic moments estimated from the experimental data.
In summary, we were able to detect the XMCD signal
at both the Si L3,2and Si K absorption edge respectively
for highly ordered Fe3Si films on a MgO tunnel barrier.
Orbital and spin magnetic moments are aligned antiparallel
to the magnetic moments of Fe and could be quantified by
comparison to calculated spectra. While the spin magnetic
moment of Si μeff
s=(0.011 ±0.005) μBis estimated to be
smaller than predicted by theory, the orbital magnetic moment
μl=(0.003 ±0.003) μBis about twice as large as the
theoretically expected value. Both reduced spin and enhanced
orbital magnetic moment may be explained by the surface
sensitivity of the TEY mode employed in this work, a possible
Si-enrichment in the surface layer of Fe3Si, and uncertainties
in the calculated XANES amplitudes.
In addition, the field dependence of the XMCD at the Si
K edge as a measure of the change of orbital magnetization
with the applied external magnetic field could be obtained. Our
findings demonstrate the possibility to detect extremely weak
induced magnetic moments and use them for the determination
C. ANTONIAK et al. PHYSICAL REVIEW B 85, 214432 (2012)
of local atomic structures through synergistic theoretical and
experimental work.
We would like to thank P. Wulkow (U. Duisburg-Essen)
for help in the measurements and the HZB BESSY II staff,
especially H. Pfau and R. Schulz for their kind support. Funded
by BMBF (05 ES3XBA/5) and DFG (SFB 491). Work in the
UCI was supported by US-DOE grant DE-FG02-05ER46237.
Calculations were performed on parallel computers at NERSC.
J.L. thanks the Alexander von Humboldt Foundation for
support through the Feodor Lynen program.
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... Element sensitivity of the Ni and of the Si layer is achieved by resonantly tuning the FEL radiation at the Ni M 2,3 edge [23] and the Si L 2,3 edge [24]. The applied magnetic field B, whose direction is parallel to the k-vector of the incoming FEL radiation, orients the magnetization of Ni along the line of intersection between the sample surface and the plane of incidence. ...
Full-text available
Understanding how a spin current flows across metal-semiconductor interfaces at pico- and femtosecond timescales has implications for ultrafast spintronics, data processing and storage applications. However, the possibility to directly access the propagation of spin currents on such time scales has been hampered by the simultaneous lack of both ultrafast element specific magnetic sensitive probes and tailored metal-semiconductor interfaces. Here, by means of free electron laser-based element sensitive Kerr spectroscopy, we report direct experimental evidence of spin currents across a Ni/Si interface in the form of different magnetodynamics at the Ni M2,3 and Si L2,3 absorption edges. This further allows us to calculate the propagation velocity of the spin current in silicon, which is on the order of 0.2 nm/fs.
... The XANES and XMCD spectra recorded at the Al K edge are shown in Fig. 2. The XANES spectral shape reflects the Al empty density of states of p symmetry and from this perspective resembles the K-edge spectra measured for metalloids, e.g., Ge or Si [47,48] in intermetallics. A strong XMCD signal, as high as 1.5% with respect to the edge jump, is observed at the Al K edge. ...
Herein we show that Mo4Ce4Al7C3, a recently discovered nanolamellar compound displaying mixed valence, combines Kondo lattice behavior with ferromagnetism. A sizeable magnetization is carried by 3p states of Al as evidenced by a strong x-ray magnetic circular dichroism signal at the K edge of aluminum, whereas no detectable signal was observed at the K edge of carbon and L2,3 edges of molybdenum. These results point out that the ferromagnetic behavior originates in the Ce atoms with 4f1 electronic configuration lying within the Al planes. The evolution with pressure of the mixed valence of Ce atoms in the Mo-C planes determined via Ce L3 x-ray-absorption spectra along with the magnetoresistance measurements across the ferromagnetic transition unambiguously reveal a Kondo behavior. Angle-resolved photoemission spectroscopy and density functional theory confirm a certain degree of Ce 4f electron delocalization. More generally, conduction electrons are not restricted to lie in the MoC planes but are also delocalized in the Al planes.
... The XANES and XMCD spectra recorded at the Al K edge are shown in Fig. 2. The XANES spectral shape reflects the Al empty density of states of p symmetry and from this perspective resembles the K-edge spectra measured for metalloids, e.g., Ge or Si [47,48] in intermetallics. A strong XMCD signal, as high as 1.5% with respect to the edge jump, is observed at the Al K edge. ...
Herein we show that Mo4Ce4Al7C3, a recently discovered nanolamellar compound displaying mixed valence, combines Kondo lattice behavior with ferromagnetism. A sizeable magnetization is carried by 3p states of Al as evidenced by a strong x-ray magnetic circular dichroism signal at the K edge of aluminum, whereas no detectable signal was observed at the K edge of carbon and L2,3 edges of molybdenum. These results point out that the ferromagnetic behavior originates in the Ce atoms with 4f1 electronic configuration lying within the Al planes. The evolution with pressure of the mixed valence of Ce atoms in the Mo-C planes determined via Ce L3 x-ray-absorption spectra along with the magnetoresistance measurements across the ferromagnetic transition unambiguously reveal a Kondo behavior. Angle-resolved photoemission spectroscopy and density functional theory confirm a certain degree of Ce 4f electron delocalization. More generally, conduction electrons are not restricted to lie in the MoC planes but are also delocalized in the Al planes.
... A quantitative analysis here would be rather difficult because we cannot differentiate the XAS signals coming from the film and the substrate. However, theoretical calculations of RE functionalized silicene [42] predict tiny magnetic moments on Si, on the order 10 -2 -10 -3 B; the Si K signal in GdSi2 is comparable to that in Fe3Si, a non-layered ferromagnet [43]; the Ge K XMCD signal in EuGe2 is much lower than that in other FM Ge-based compounds [44]. Both Si K and Ge K XMCD signals in the REXenes have similar spectral shapes and the same sign which indicates that the p states (probed at the K edge) are spinpolarized in a similar manner. ...
2D magnets have recently developed into a class of stoichiometric materials with prospective applications in ultra-compact spintronics and quantum computing. Their functionality is particularly rich when different magnetic orders are competing in the same material. Metalloxenes REX2, silicene or germanene-heavy counterparts of graphene-coupled with a layer of rare-earth metals, evolve from 3D antiferromagnets in multilayer structures to 2D ferromagnets in a few monolayers. This evolution, however, does not lead to fully saturated 2D ferromagnetism, pointing at a possibility of coexisting/competing magnetic states. Here, REX2 magnetism is explored with element-selective X-ray magnetic circular dichroism. The measurements are carried out for GdSi2, EuSi2, GdGe2 and EuGe2 of different thickness down to 1 monolayer employing K absorption edges of Si and Ge as well as M and L edges of the rare-earths. They access the magnetic state in REX2, determine the seat of magnetism, orbital and spin contributions to the magnetic moment. High-field measurements probe remnants of the bulk antiferromagnetism in 2D REX2. The results provide a new platform for studies of complex magnetic structures in 2D materials.
... In the mentioned bulk materials, the spin liquid properties have been identified through the temperature dependence of the magnetic susceptibility. Measuring this quantity for the surface spins in Si(553)-Au represents an experimental challenge, but could possibly be achieved by x-ray magnetic circular dichroism (XMCD) experiments at the Si K and L edges [34]. ...
Full-text available
Adsorption of Au on Si(553) results in the self-assembly of highly ordered step arrays of one-dimensional (1D) Au atomic wires along the step direction. Charge transfer from the terrace to the step edge causes every third Si atom at the step edge to exhibit a partially filled dangling bond hosting a single fully spin-polarized electron which forms in an ordered 1D spin chain along the step. The interstep correlation of this threefold periodicity in neighboring Si step edges and the geometry of the unit cell has been determined by means of high-resolution spot profile analysis low-energy electron diffraction, scanning tunneling microscopy, and density functional theory. While the twofold periodicity of the Au wires exhibits a weak interwire interaction, leading to streaks in the diffraction pattern, the correlation of the Si step edge atoms is by far a stronger interaction, resulting in clear spots. The corresponding unit cell spanned by threefold ordered step edge atoms can be described as a centered structure which is magnetically frustrated and may stabilize a (two-dimensional) quantum spin liquid.
... An XMCD signal of induced nature on a metalloid element is not uncommon in ferromagnetic intermetallic alloys. It has for instance been observed on Si in Fe 3 Si [34], on S in EuS and Fe 7 S 8 [35,36], and on As in (Ga,Mn)As [37]. However, we are not aware of any attempt to measure magnetic polarization of 3p states of phosphorus. ...
Full-text available
To study the evolution of the electronic states and magnetism of the metallic and metalloid atoms across the first-order ferromagnetic transition of (Mn,Fe)2(P,Si,B) compounds, x-ray absorption (XAS) and magnetic circular dichroism (XMCD) spectra were recorded at the K edges of P, Mn, and Fe. Surprisingly, while the Fe and Mn XAS spectra do not show pronounced changes, the K-edge XAS of P is strongly modified across the ferromagnetic transition and is a fingerprint of electronic structure changes at the phase transition. The evolution of the 3p electronic states of phosphorus is linked to changes in metal-metalloid bonding. The amplitude of this effect is correlated to the discontinuity in interatomic distances at the transition and progressively disappears with boron substitution. Moreover, it is found that the P atoms carry a finite magnetic moment in the ferromagnetic state in accordance with the results of band-structure calculations.
... The highest photon energy used so far with elliptical polarization was 1853 eV for resonant excitation of the Si 1s edge. In that experiment, induced magnetic moments in Heusler-like Fe 3 Si were studied (Antoniak et al., 2012). Further prominent publications from the PM3 beamline can be found in additional references (Valencia et al., 2011;Radu et al., 2012;Antoniak et al., 2011;Mishra et al., 2009;Sanyal et al., 2010). ...
Full-text available
A new but yet well proven way of making elliptically polarized dipole radiation from the BESSY II storage ring applicable to the SX700-type collimated plane-grating monochromator PM3 is described. It is shown that due to the limited vertical acceptance of the grating a simple use of vertical apertures is not possible in this case. Rather, deflecting the beam upwards or downwards by rotating the vertically collimating toroidal mirror M1 around the light axis leads to excellent performance. The resulting detuning of the photon energy can be taken into account by a readjustment of the monochromator internal plane mirror M2. The energy resolution of the beamline is not affected by the non-zero `roll' of the collimating mirror.
We present a combined investigation of the electronic structure of bulk arc-melted full-Heusler Co2-xFe1+xSi (x = 0, 0.5, 1) and CoFeSi alloys using density functional theory and ultrasoft X-ray emission spectroscopy. We perform first-principles calculations of the spin-polarized total and partial density of states for the Co and Fe 3d (s, p) as well as for the Si 3s (p, d) orbitals. It is demonstrated that only Co2FeSi alloy exhibits a half-metallic behavior. However, the inverse CoFe2Si alloy shows pseudogap and high spin polarization at the Fermi level. We carry out ultrasoft X-ray emission Si L2,3 measurements, which provide the information about the local partial density of states of Si 3s and 3d orbitals in the valence band localized on Si atoms. We compare the measured spectra with our theoretical calculations and discuss them in terms of the contribution of s and d-electrons to the bonding. The Si and transition-metals sd and dd bonding formation is shown in the Co2-xFe1+xSi and CoFeSi alloys. The high spin polarization values, along with the extremely high Curie temperature, make these compounds potential candidates for spintronic applications.
The effect of ordering degree on electronic structures and magnetism of Fe3Si alloys were investigated scientifically using first principles calculations based on plane‐wave pseudo‐potential theory. The studied results of heat of formation and cohesive energy for D03 and B2 structures of Fe3Si reveal that the order of structural stability from high to low is B2‐9, B2‐8, B2‐7, B2‐6, D03/B2‐1, B2‐2, B2‐3, B2‐4, B2‐5. Both D03 and B2 structures of Fe3Si exhibit the metallic feature. A wider breadth of the pseudo‐gap with occupation of Si sites by more Fe[B] atoms except B2‐5 implies that the hybridization and covalent bond are intensified. Meanwhile, with substitution of Fe[B] atoms by more Si atoms, the stability of system improves because the Fermi level is nearer to the bottom of the pseudo‐gap. The origination of ferromagnetism for ordered Fe3Si except B2‐9 is mainly from the Fe 3d spin polarization. Compared with D03 structure of Fe3Si, an increment in the concentration of Fe atoms with occupation of Si sites by more Fe[B] atoms causes the change of interaction between Fe and Si atoms and the total magnetic moment increases. On the contrary, the total magnetic moment decreases with gradual substitution of Fe[B] atoms by Si atoms. This article is protected by copyright. All rights reserved.
X-ray magnetic circular dichroism (XMCD) provides an experimental access to element-specific electronic properties of thin epitaxial films of Heusler alloys. The combination of bulk-sensitive transmission and surface-sensitive electron yield methods reveals quantitative information on bulk and interface properties. Extreme cases of magnetically dead and life layers at interfaces illustrate the high potential of XMCD. The dependence of XMCD on disorder, structure and composition is discussed as well as dynamic properties investigated by a combination of ferromagnetic resonance and XMCD. Examples are shown where spectroscopic information provided by XMCD is exploited to discuss subtle changes of the partial density of states (PDOS) as a function of composition, magnetization direction and temperature.
Full-text available
A site population analysis of iron atoms in Fe3Si alloys with D03 superlattice structure was performed by 57Fe Mössbauer spectroscopy using crushed and annealed powder specimens with silicon concentrations of 23.3 and 25.5 at%. The Mössbauer spectra obtained were found to be superpositions of at least three six-line components. The relative intensity for each component has been analyzed using the thin foil approximation. The atomic configuration and the relative number of iron atoms of the component were determined from the values of the hyperfine field and the relative intensity for each component, and from these data the short-range-order parameter was determined.In order to determine the long-range-order parameters of the alloys, a two step procedure was used: First, the perfectly ordered D03 lattice of 25 at% Si was constructed by computer, and then atoms were replaced randomly so that any desired values of the alloy concentration and the degree of order are reached. By comparing the computer simulation with the result of the Mössbauer experiment, the long-range-order parameters, S(D03) and S(B2), were determined. The values agree well with those obtained by the powder X-ray diffraction technique.
Full-text available
We have calculated the spin-polarization effects of a current in a two-dimensional electron gas which is contacted by two ferromagnetic metals. In the purely diffusive regime, the current may indeed be spin-polarized. However, for a typical device geometry the degree of spin-polarization of the current is limited to less than 0.1% only. The change in device resistance for parallel and antiparallel magnetization of the contacts is up to quadratically smaller, and will thus be difficult to detect.
Full-text available
Dramatic advances in the understanding of x-ray absorption fine structure (XAFS) have been made over the past few decades, which have led ultimately to a highly quantitative theory. This review covers these developments from a unified multiple-scattering viewpoint. The authors focus on extended x-ray absorption fine structure (EXAFS) well above an x-ray edge, and, to a lesser extent, on x-ray absorption near-edge structure (XANES) closer to an edge. The discussion includes both formal considerations, derived from a many-electron formulation, and practical computational methods based on independent-electron models, with many-body effects lumped into various inelastic losses and energy shifts. The main conceptual issues in XAFS theory are identified and their relative importance is assessed; these include the convergence of the multiple-scattering expansion, curved-wave effects, the scattering potential, inelastic losses, self-energy shifts, and vibrations and structural disorder. The advantages and limitations of current computational approaches are addressed, with particular regard to quantitative experimental comparisons.
Full-text available
The percentage of substitutional doping of magnetic atoms (Mn) in group-IV-based dilute magnetic semiconductors can be increased by codoping with another conventional electronic dopant, as demonstrated from first-principles calculations recently [W. G. Zhu, Z. Y. Zhang, and E. Kaxiras, Phys. Rev. Lett. 100, 027205 (2008)]. Here, we report extensive theoretical investigations of the kinetic and thermodynamic characteristics of several codoped systems including bulk Si and Ge as hosts and various group-III and group-V dopants. The main findings are as follows. The n-p pairing of n -type codopants with p -type substitutional Mn is energetically stable in bulk Ge and Si. Mn atoms move from interstitial sites to substitutional sites easier (with lower kinetic barriers) in the presence of a neighboring n -type codopant. Magnetic coupling between two Mn atoms in bulk Ge oscillates between positive (ferromagnetic) and negative (antiferromagnetic) values with increasing Mn-Mn distance, but in Mn/As codoped Ge the coupling parameter remains positive at all distances beyond nearest neighbors and this qualitative difference does not change with the doping level. For Mn-doped Si, all coupling values except for the nearest-neighbor one are positive and do not change much upon codoping. We find an unconventional magnetic anisotropy in the codoped system, that is, the dependence of magnetic coupling on the relative positions of the magnetic ions and their neighboring donors. We map the calculated magnetic coupling to a classical Heisenberg model and employ Monte Carlo simulations to estimate the Curie temperature (Tc) . We find that in Mn-doped Ge no ferromagnetic order exists for Mn concentrations ranging from 3.13% to 6%. Instead, a spin-glass phase transition occurs at ˜5K at 5% Mn doping. For Mn/As codoped Ge, Tc increases nearly linearly with the Mn concentration and reaches 264 K at 5% Mn doping.
The calculations of Ti K-edge X-ray absorption near-edge structures (XANES) in fresnoite Sr2TiSi2Og are carried out using multiple-scattering method. The origins of the pre-edge peak along with the fine structures in the main peak of Ti K-edge XANES are interpreted by comparing the calculations in various modified structure models. It concludes that the pre-edge peak is dominantly determined by the structure (including both coordination and bond lengths) within the nearest-neighbor distance, while the fine structures beyond the pre-edge peak region are sensitively determined by the structure extending to the medium-range distance.
A new formalism for determining highly accurate total energies of solids within density functional theory is presented in which all necessary terms are easily obtained from the energy-band calculation. A major feature of this all-electron approach is the explicit algebraic cancellation of the nuclear Coulomb singularities in the kinetic and potential energy terms which leads to good numerical stability. As an illustration, the method is implemented in the full-potential linearized augmented-plane-wave method for thin films and applied to monolayers of Cs and graphite. The structural information (lattice parameters, force constants, etc.) for graphite are found to be in very good agreement with experiment on bulk graphite and to be rather insensitive to the quality of the basis. The calculated cohesive energy (relative to a spin-polarized local-density atom), on the other hand, is quite sensitive to the quality of the basis; a limited basis yields results in fortuitous agreement with experiment. The converged result for the cohesive energy is found to be 17% too large compared to experiment, an error which appears to arise from the neglect of correlation with near-lying excited configurations in the local-density atom and not to errors in the condensed system.
The "M\"ossbauer" technique was used to measure the internal magnetic fields and isomer shifts of ${\mathrm{Fe}}^{57}$ atoms residing at various sites in the FeSi series. The relative abundances of the various sites present in a given alloy were obtained by measuring the relative intensities of the components in the resolved spectrum of the alloy. Alloys with Si content varying from 0 to $\sim${}27 at.% were studied. In the disordered region (10 at.% Si) three different type sites were observed. These corresponded to Fe atoms having 8, 7, and 6 nearest-neighbor Fe atoms. The internal field decreased by $0.08 {H}_{\mathrm{Fe}}$ for each Si nearest neighbor. In the ordered region the alloys try to go into a ${\mathrm{Fe}}_{3}$Al type structure. Sites having 8 through 3 nearest-neighbor iron atoms were observed. For $A$-type sites (4 nearest-neighbor Fe atoms and 4 nearest-neighbor Si atoms at 25 at.% Si), the internal field decreased by $0.14 {H}_{\mathrm{Fe}}$ for each Si nearest neighbor. Over the whole series the isomer shift indicated that there was progressively less electronic charge density at the origin as the number of nearest-neighbor Si atoms increased. A measure of the relative intensities of the various magnetic field components in the spectra of an alloy series is shown to give direct evidence on the type of ordering. No tendency to form intermediate compounds other than ${\mathrm{Fe}}_{3}$Si was observed. An average internal magnetic field for each alloy could be obtained from the data. This average internal field does not vary in the same way as the magnetization on the FeSi series.
Using the density functional full-potential linearized augmented plane wave approach, the x-ray absorption and magnetic circular dichroism (XMCD) spectra of Ga1-xMnxAs are calculated. Significantly, XMCD of Mn is highly sensitive to the change in environment, and thus can be utilized to characterize impurity distribution. The nature of Mn-induced spin polarization on Ga and As sites, vital for the carrier mediated magnetic ordering, is discussed in light of computational and experimental results.
First-principles electronic structure studies based on local spin density functional theory and performed on extremely complex simulations of ever increasingly realistic systems, play a very important role in explaining and predicting surface and interface magnetism. This review deals with what is a major issue for first-principles theory, namely the theoretical/computational treatment of the weak spin–orbit coupling in magnetic transition metals and their alloys and its important physical consequences: magneto-crystalline anisotropy, magnetostriction, magneto-optical Kerr effects and X-ray magnetic circular dichroism. As is demonstrated, extensive first-principles calculations and model analyses now provide simple physical insights and guidelines to search for new magnetic recording and sensor materials.