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Induced magnetism at the interfaces of a Fe/V superlattice investigated by resonant magnetic x-ray scattering
Supplementary resource (1)
... Magnetization depth-profiling of multilayers is possible to implement by several methods: by polarized neutron reflectivity, Mössbauer (nuclear resonant) reflectivity and X-ray resonant magnetic reflectivity (XRMR). Polarization-dependent resonant X-ray reflectivity measurements performed with soft [1][2][3] and hard [4][5][6][7] radiation gain by their element and electronic shell selectivity. The most valuable achievementsof XRMR refer to the induced magnetic moment investigations. ...
... With inserted 57 Fe test monolayers the 57 Fe magnetic moment distribution across one period was investigated via the measured hyperfine fields in CEMS experiments [53] or by nuclear resonant scattering and polarized neutron scattering [54]. Induced magnetism on V atoms at the interfaces of a Fe/V superlattice has been investigated by resonant magnetic X-ray scattering [3]. The present investigation of the [ 57 Fe(10 ML)/V(20 ML)] 20 sample by Mössbauer reflectivity with polarization analysis devoted to the surface layer characterization. ...
Polarization analysis of the reflected radiation has been performed in Mössbauer reflectivity measurements with a Synchrotron Mössbauer Source (SMS). Effective π→σ′ polarization selection is attained with LiF crystal ((6 2 2) 90o-reflection for 14.4 keV radiation, angular acceptance ∼ 100``) capable of high π→π′ suppression. Basic features of the reflectivity with the rotated π→σ′ polarization are revealed in the experiment with the [⁵⁷Fe(10 ML)/V(20 ML)]20 multilayer. Selection of π→σ′ polarization component in Mössbauer reflectivity allows to exclude nonresonant electronic scattering, besides Mössbauer π→σ′ reflectivity spectra (R-spectra) contain only contributions from magnetized along the beam ferromagnetic phases. The antiferromagnetic iron oxides do not contribute to π→σ′ R-spectra (dichroic component is compensated). Therefore, in the Mössbauer reflectivity experiment supplemented by polarization analysis the data interpretation becomes more certain and gives information about depth position for ferromagnetic layers selectively. With this new technique we locate antiferromagnetic iron phases in the very top layer of [⁵⁷Fe(10 ML)/V(20 ML)]20 multilayer and ascertain the ferromagnetic ordered iron layers in the remaining part of the structure. This new approach in Mössbauer reflectivity has interesting perspectives for investigations of hyperfine interactions for iron complexes on the surface, ultrathin layers and multilayers with complicated magnetic structures.
... It is element specific and has a high sensitivity that allows the measurements of extremely low magnetic signals [25]. The XMCD signal is an average over all atoms of each specie and it is not possible to separate the signal of different layers of the same element as is the case of X-ray resonant magnetic scattering (XRMS) [26,27]. Despite that, since magnetic induction is an interfacial phenomenon and XMCD is more sensitive to the surface, the averaging is restrict to only the interface and a few monolayers. ...
... The hybridization of d-orbitals by the proximity effect at a NM/FM interface influences the electronic and magnetic properties of both materials, and the NM can become FM in thin films and multilayers where the density of states is enhanced by band narrowing [22][23][24][25][26][27][28]. It can lead to the induction of magnetism even in materials that have Stoner parameters far away from the unity required to fulfill Stoner criterion for a FM stability. ...
The induced magnetization in Cu atoms at the interface between ferromagnetic (FM) Fe/Co ultrathin films and a nonmagnetic (NM) Cu3Au(001) substrate was explored by the investigation of two structures of five alternated Fe and Co monoatomic layers with different stacking orders with a Fe or a Co layer in direct contact with the Cu3Au(001) surface. First principles calculations were applied to disentangle the origin of magnetic proximity effects at these FM/NM interfaces. The hybridization between the electronic states of the FM layers, resulting in a pronounced widening of the d-bands of the local density of states of Fe-Co interface atoms, has a fundamental effect in the spin-polarization of the NM substrate. X-ray magnetic circular dichroism measurements at the L2,3 edges of Fe, Co and Cu allowed to extract the spin and orbital magnetic moments of Fe and Co, and to measure extremely low magnetic moments induced in Cu atoms. It is shown that the magnetism is induced only in the Cu and Au atoms at the first CuAu monolayer at the very surface of the substrate, i.e., the Cu XMCD signal is due to only 0.5 ML magnetic Cu atoms.
... The magnetic interaction between ferromagnetic layers across a non-magnetic metal spacer layer is of particular interest in application of low-dimensional magnetic systems owning to several interesting phenomena and properties, such as giant magnetoresistance, oscillating interlayer coupling and perpendicular magnetic anisotropy [1][2][3]. Fe/V superlattices have been a benchmark for various studies on such nanoscale magnetic systems [4][5][6][7][8][9]. The system shows a great variety of magnetic structures depending on the thickness of the individual Fe-and V-layer, chemical ordering and quality of the interface [4,5,[10][11][12]. ...
The magnetic properties of the Fe/V superlattices were studied by conventional Conversion Electron Mössbauer Spectroscopy (CEMS) and online 57Fe+ emission Mössbauer Spectroscopy (eMS) at room temperature (RT) at ISOLDE/CERN. The unique depth-enhanced sensitivity and ultradiluted regime of the probe atoms adopted in this eMS facility enabled the investigation of the magnetic structures and the strain state in the superlattice layers and at the interfaces. The magnetic spectra of the superlattices were found to depend on both the local lattice environment and the strain state of the Fe-lattices. The magnetic polarisation in the V-layers or at the interfaces was not detected at RT. Spectral broadening was evident in the single line component of the eMS due to Fe ions substituted at V-lattice sites in the V-layers of the superlattice, attributable to the lattice strain in the V-layers. Our study demonstrate that with the online eMS technique the effects of the strain state of the superlattice on the magnetic properties of the Fe-layer in the Fe/V multilayer structures can be detected.
... nm)) 3 have been investigated using the surface magneto-optical Kerr effect [2]. The x-ray diffraction was used to study the: Fe/V [12], La 0.7 Ca 0.3 MnO 3 /Pr 0.58 Ca 0.42 MnO 3 [5] and Mn 3 O 4 /Fe 3 O 4 superlattices [6]. The spin order of bulk MnSi, MnSi film, and the CoSi/ MnSi superlattice is investigated using first-principles calculations based on full-potential linearized augmented plane-wave based density functional theory [13]. ...
... Fe/V multilayers (MLs) have been used recently as a model system in studies of interlayer exchange coupling (IEC) [1][2][3], proximity effect [4][5][6], and hydrogen absorption [7][8]. The experiments on IEC performed previously have been limited to the second and third antiferromagnetic (AFM) maxima [1] or measurements at room temperature [3]. ...
... Hence, besides the existing controversial theoretical interpretations about which type of AFM coupling dominates (i.e., in-plane or out-of-plane), the evident disagreement between theory (AFM) and experiment (FM) in determining the lower energy magnetic ordering in Cr 2 GeC calls for the need of further experimental and theoretical efforts [72,155,17,116,156]. Experimentally, an alternative and more bulk-sensitive spectroscopic technique than XMCD [50], such as resonant magnetic X-ray scattering (XRMS) [157] utilizing constructive interference at suitable Bragg scattering angles [21] would be more useful for measuring weak magnetic signals in nanolaminates. ...
This is a critical review of MAX-phase carbides and nitrides from an electronic-structure and chemical bonding perspective. This large group of nanolaminated materials is of great scientific and technological interest and exhibits a combination of metallic and ceramic features. These properties are related to the special crystal structure and bonding characteristics with alternating strong M\ \C bonds in high-density MC slabs, and relatively weak M\ \A bonds between the slabs. Here, we review the trend and relationship between the chemical bonding, conductivity , elastic and magnetic properties of the MAX phases in comparison to the parent binary MX compounds with the underlying electronic structure probed by polarized X-ray spectroscopy. Spectroscopic studies constitute important tests of the results of state-of-the-art electronic structure density functional theory that is extensively discussed and are generally consistent. By replacing the elements on the M, A, or X-sites in the crystal structure, the corresponding changes in the conductivity, elasticity, magnetism and other material properties make it possible to tailor the characteristics of this class of materials by controlling the strengths of their chemical bonds.
... Hence, besides the existing controversial theoretical interpretations about which type of AFM coupling dominates (i.e., in-plane or out-of-plane), the evident disagreement between theory (AFM) and experiment (FM) in determining the lower energy magnetic ordering in Cr 2 GeC calls for the need of further experimental and theoretical efforts [72,155,17,116,156]. Experimentally, an alternative and more bulk-sensitive spectroscopic technique than XMCD [50], such as resonant magnetic X-ray scattering (XRMS) [157] utilizing constructive interference at suitable Bragg scattering angles [21] would be more useful for measuring weak magnetic signals in nanolaminates. ...
This is a critical review of MAX-phase carbides and nitrides from an electronic-structure and chemical bonding perspective. This large group of nanolaminated materials is of great scientific and technological interest and exhibits a combination of metallic and ceramic features. These properties are related to the special crystal structure and bonding characteristics with alternating strong MC bonds in high-density MC slabs, and relatively weak MA bonds between the slabs. Here, we review the trend and relationship between the chemical bonding, conductivity, elastic and magnetic properties of the MAX phases in comparison to the parent binary MX compounds with the underlying electronic structure probed by polarized X-ray spectroscopy. Spectroscopic studies constitute important tests of the results of state-of-the-art electronic structure density functional theory that is extensively discussed and are generally consistent. By replacing the elements on the M, A, or X-sites in the crystal structure, the corresponding changes in the conductivity, elasticity, magnetism and other material properties make it possible to tailor the characteristics of this class of materials by controlling the strengths of their chemical bonds.
... The magnetic interaction between ferromagnetic layers across a non-magnetic metal spacer layer is of particular interest in application of low-dimensional magnetic systems owning to several interesting phenomena and properties, such as giant magnetoresistance, oscillating interlayer coupling and perpendicular magnetic anisotropy [1][2][3]. Fe/V superlattices have been a benchmark for various studies on such nanoscale magnetic systems [4][5][6][7][8][9]. The system shows a great variety of magnetic structures depending on the thickness of the individual Fe-and V-layer, chemical ordering and quality of the interface [4,5,[10][11][12]. ...
A semicontinuous module reactor was operated under methanophilic conditions to effect rapid solid anaerobic digestion of lignocellulose substances for waste utilization and stabilization. This was achieved by recovering the methanogenic phase from the high-rate acidogenic fermentation phase. The influence of a total carbon to nitrate ratio (C/N(NO3)) of the lignocellulose feed on the development of methanogens from a high-rate acidification fermentation phase was first investigated. The effects of pH adjustment and dilution of the high-rate acidification fermentation phase using the two-phase anaerobic digestion configuration were subsequently evaluated. The results showed that an increase in the C/N(NO3) ratio of the feed substrate could promote the development of methanogens as a result of the restraint of denitrification during or after the acidification fermentation phase. In-process neutralization of the digestion pH and dilution of the digestion intermediate products could reduce the inhibition from the high-rate acidification fermentation phase. The integrated digestion process promoted the biotransformation of lignocellulose residues from the high-rate acidification phase to the methanogenic phase and ultimately stabilized digestion.
In this paper, the thermodynamic, magnetic properties and magnetocaloric effect of an infinite three-layers thin film superlattices(A,B,C) formed by (1,3/2,2) mixed spins were investigated via Monte Carlo study. The influence of intralayer, interfacial exchange interactions, thickness of the film and temperature on the magnetization, magnetic susceptibility, internal energy and magnetic specific heat was investigated. The grounds states in various parameters plane are given. The results show that the intralayer and the interfacial interface the exchange couplings, the thickness of the layer and the concentration of atoms have important influences on the magnetization, the susceptibility, the internal energy and the specific heat of the system. The phase diagrams in various parameters planes are obtained and have different impact on critical temperature of the system. The "double peak" and "triple peak" in thermal magnetic susceptibility, magnetic specific heat, normalized magnetic entropy change are obtained. The magnetic hysteresis cycle and normalized magnetic entropy change have been obtained under the effect of couplings and the thickness of the film. In addition, a number of interesting phenomena have been found, such as: double peak and triple peak in susceptibility and specific heat curves, resulting from the difference in temperature dependence of three sublattice magnetization.
In the early 1960s, scientists achieved the breakthroughs in the fields of solid surfaces and artificial layered structures. The advancement of surface science has been supported by the advent of ultra-high vacuum technologies, newly discovered and established scanning probe microscopy with atomic resolution, as well as some other advanced surface-sensitive spectroscopy and microscopy. On the other hand, it has been well recognized that a number of functions are related to the structures of the interfaces, which are the thin planes connecting different materials, most likely by layering thin films. Despite the scientific significance, so far, research on such buried layers and interfaces has been limited, because the probing depth of almost all existing sophisticated analytical methods is limited to the top surface. The present article describes the recent progress in the nanometer scale analysis of buried layers and interfaces, particularly by using X-rays and neutrons. The methods are essentially promising to non-destructively probe such buried structures in thin films. The latest scientific research has been reviewed, and includes applications to bio-chemical, organic, electronic, magnetic, spintronic, self-organizing and complicated systems as well as buried liquid-liquid and solid-liquid interfaces. Some emerging analytical techniques and instruments, which provide new attractive features such as imaging and real time analysis, are also discussed.
We present the magnetic properties of bcc Fe films on and embedded in bcc-V(100) substrates in their paramagnetic phase above the Curie temperature. We have used a first-principles electronic structure method based on the spin-density functional theory and the spin fluctuations in the paramagnetic phase are described using the disordered local moments model. We have calculated the local magnetic moments, magnetic correlations and the Curie temperature of several Fe/V(100) and V/Fe/V(100) systems. In general, the Fe layers in close proximity to V have their magnetic moments suppressed, while in the interior of the film, the value of the magnetic moment oscillates from one layer to the other. When the films are capped by a V layer, the magnitudes of the magnetic moments decreases. The Curie temperature also shows an interesting oscullatory behaviour as the V capping layer thickness is increased. In the Fe/V/Fe/V(100) films, we observed that the exchange interactions between the two Fe layers across the spacer exhibits an oscillating behaviour.
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The element and electronic shell selectivity of x-ray resonant magnetic scattering (XRMS) has been used to investigate the profile of the spin polarization of the 5d electronic states of Ce and La across the rare-earth layers in Ce/Fe and La/Fe multilayers. The magnetic contributions to the diffracted intensities have been measured at low angles, at the L2 edge of the rare earth. In agreement with previous results from x-ray magnetic circular dichroism (XMCD) experiments, the La 5d polarization is found to be localized right at the interfaces with the Fe layers, as it is expected from a direct hybridization with the Fe 3d states. In the case of Ce/Fe multilayers where Ce is in an α-like electronic state with a complex behavior of the 5d magnetic polarization, the XRMS results obtained for two samples with 10 and 22 Å thick Ce layers indicate that the Ce 5d polarization decreases slowly from the interfaces towards the center of the layers. This is in agreement with previous XMCD results. However, at least for the two samples which have been investigated, XRMS also suggests that the Ce 5d polarization oscillates across the Ce layer with a period equal to the (111) interplanar distance in α fcc Ce. Though compatible with the XMCD findings, this oscillating behavior cannot be derived from its dependence on the Ce layer thickness because of the decrease of the magnetic polarization which prevents us from observing changes in the sign of the XMCD amplitude.
We report the results of an x-ray-scattering study of the polarization and resonance properties of the magnetic cross section of holmium. Off resonance, we have measured the degree of linear polarization for several different chemical and magnetic reflections, and shown that the results are consistent with a nonresonant description of the x-ray-scattering cross section. When the incident x-ray energy is tuned near the {ital L}{sub III} absorption edge, large resonant enhancements of the magnetic scattering, and resonant integer harmonics, are observed. Detailed measurements of the dependence of the integrated magnetic intensity on the incident x-ray energy, on the x-ray momentum transfer, and on the sample temperature are described for incident x-ray energies in a range of 250 eV below and above the {ital L}{sub III} absorption edge. In addition, we have characterized the energy dependence of the linearly {sigma}- and {pi}-polarized components of the magnetic scattering in this range, and fitted the resulting line shapes to a simple model of the resonant cross section, including electric dipole and quadrupole transitions among atomic orbitals. The most striking feature of the line shapes is their asymmetry, which results from the interference of the resonant and nonresonant cross sections. Smaller resonant enhancements of the magnetic scattering are reported for incident x-ray energies tuned near the {ital L}{sub II} and {ital L}{sub I} absorption edges.
We have studied the magnetoresistance of (001)Fe/(001)Cr superlattices prepared by molecular-beam epitaxy. A huge magnetoresistance is found in superlattices with thin Cr layers: For example, with tCr=9 Å, at T=4.2 K, the resistivity is lowered by almost a factor of 2 in a magnetic field of 2 T. We ascribe this giant magnetoresistance to spin-dependent transmission of the conduction electrons between Fe layers through Cr layers.
By measuring the degree of linear polarization we identify the orbital and spin contributions to the x-ray magnetic scattering in holmium. When the incident x-ray energy is tuned through the LIII absorption edge, we observe a fiftyfold resonant enhancement of the magnetic signal, and resonant integer harmonics. The line shapes of the two linear components scattered parallel and perpendicular to the diffraction plane are distinct in energy with a 6-eV splitting.
Magnetization and magnetoresistivity studies of Fe/V (001) superlattices are reported. The first giant magnetoresistance peak with respect to the vanadium and iron layer thicknesses is investigated. The interlayer antiferromagnetic coupling strength is found to show a peak at a vanadium layer thickness of 13 atomic monolayers ($\approx$ 20 \AA) with a full width at half maximum of about 2 monolayers. The antiferromagnetic coupling shows a maximum at an iron layer thickness of about 6 monolayers ($\approx$ 9 \AA) for series of superlattices with vanadium thicknesses around 13 monolayers. The magnitude of the giant magnetoresistance shows a similar variation as the antiferromagnetic coupling strength. Comment: REVTeX 4 style; 8 pages, 7 figures. The TEM picture (Fig. 3) is also included in GIF format (TEM.gif)
This text describes optics mainly in the 10 to 500 angstrom wavelength region. These wavelengths are 50 to 100 times shorter than those for visible light and 50 to 100 times longer than the wavelengths of medical x rays or x-ray diffraction from natural crystals. There have been substantial advances during the last 20 years, which one can see as an extension of optical technology to shorter wavelengths or as an extension of x-ray diffraction to longer wavelengths. Artificial diffracting structures like zone plates and multilayer mirrors are replacing the natural crystals of x-ray diffraction. Some of these structures can now be fabricated to have diffraction-limited resolution. The new possibilities are described in a simple, tutorial way.
Fen/Vm superlattices with n=2,4 and m=2,4,5 are studied by vibrating sample magnetometry and x-ray magnetic circular dichroism measurements. The combination of both techniques allows us to determine absolutely the induced V magnetic moment per atom. The samples with the thinnest V or Fe layers, respectively, reveal the largest induced moment of mV=-1.1μB/atom (Fe4/V2) and the strongest reduction of the Fe moment down to mFe=1.34μB/atom (Fe2/V5). In addition, we probe the orbital magnetism of Fe and discuss it with respect to previous results by ferromagnetic resonance and first principles calculations.
The magnetic properties of Fe and V in (n ML V / 5 ML Fe) (001) superlattices (n=1, 2, and 5 ML) have been investigated by measuring the magnetization dependent scattering of elliptically polarized soft x rays at various scattering angles and for photon energies across the 2p x-ray-absorption edges of both Fe and V. A quantitative estimate of the magnetic moment induced on vanadium is obtained from the analysis of the resonant scattering data.
The present text book gives an comprehensive account of magnetism, spanning the historical development, the physical foundations and the continuing research underlying the field, one of the oldest yet still vibrant field of physics. It covers both the classical and quantum mechanical aspects of magnetism and novel experimental techniques. Perhaps uniquely, it also discusses spin transport and magnetization dynamics phenomena associated with atomically and spin engineered nano-structures against the backdrop of spintronics and magnetic storage and memory applications. Despite the existence of various books on the topic, a fresh text book that reviews the fundamental physical concepts and uses them in a coherent fashion to explain some of the forefront problems and applications today was thought useful by the authors and their colleagues. Magnetism is written for students on the late undergraduate and the graduate levels and should also serve as a state-of-the-art reference for scientists in academia and research laboratories. © Springer-Verlag Berlin Heidelberg 2006. All rights are reserved.
A series of FeV multilayers was grown on polished MgO (001) substrates by dual-target magnetron sputtering. The structural quality of the samples was investigated by reflection high energy electron diffraction, low- and high-angle X-ray diffraction, reciprocal space mapping, polar scans, cross-sectional transmission electron microscopy and resistivity measurements. The results show that epitaxial FeV (001) superlattices with high crystallographic and interface quality can only be grown in a narrow substrate temperature region, 300–330 °C. The average interface roughness was estimated to be as low as ± 1 Å.
X-ray magnetic circular dichroic measurements have been performed at room temperature at the V L2,3 edges on Fe/V/Fe(110) trilayers to determine the induced V spin polarization. Contrary to similar studies on magnetic multilayers, the sample preparation and characterization were performed thoroughly in situ under ultrahigh vacuum conditions. This allowed us to modify the interfaces by tuning the deposition temperature and to probe directly the influence of interface quality on the induced V moments. The magnitude of the induced V moment increased by about a factor of 2 upon changing the deposition temperature from 300 K to 600 K. Comparison with ab initio calculations and with spectra of FeV alloys suggests that alloying at the interface results in the formation of large induced V moments.
Element-specific magnetic moments in Fe/V superlattices are studied using x-ray magnetic circular dichroism (XMCD). Superlattices are simultaneously deposited with the epitaxial orientations (100), (211), and (110), to explore the orientation dependence of these moments. The layer-averaged vanadium moments are antiparallel to those of the Fe and are larger than those observed in alloys with similar composition. The V moments decay monotonically and relatively slowly with distance from the Fe interface (exponential decay length: ) in qualitative agreement with recent calculations. In contrast to calculations, the magnitudes of the V moments fall on a universal curve for the three orientations.
The Bragg peaks in x-ray diffraction experiments are generally taken to be a reliable measure of the average lattice distance in crystals. We show that this assumption can be misleading when determining hydrogen-induced volume changes. Experiments based on simultaneous determination of the position of the Bragg peak and the sample volume of an Fe/V(001) superlattice while expanding the lattice by in situ hydrogen loading serve as an illustration of this counter-intuitive effect.
The effect of interface roughness on the induced polarization of V in polycrystalline V/Fe/V trilayers was investigated with x-ray magnetic circular dichroism, x-ray resonant magnetic scattering, and polarized neutron reflectometry. Trilayer samples were sputter deposited onto Si substrates at room temperature to minimize interdiffusion. The films were polycrystalline and exhibited an average 0.5 nm root-mean-square interfacial roughness at the Fe/V interfaces. The induced polarization found in V was constrained to the Fe/V interface extending approximately up to 2–3 monolayers into the V and exhibited antiferromagnetic alignment to the Fe layer. A magnetic moment for V ranging between −0.46 and −0.86 B / V atom is consistent with the neutron and resonant x-ray data. Notably, this value for structurally rough interfaces is significantly larger than that reported for samples with atomically flat Fe/V interfaces.
The dispersive part of the refractive index, 1−δ, of vanadium is determined by measuring the angular dependence of the Bragg peak at the V L2,3 edge energy region using a Fe/V superlattice. This X-ray scattering technique provides access to the direct determination of the dispersive part of the refractive index across an absorption resonance and to the change of values from below unity to above unity. We demonstrate that previously tabulated values tend to underestimate the amplitude of the change in the real part of the refractive index. We also examine the need for applying absorption and polarization corrections.
We describe a bending magnet beamline designed to operate on a third generation synchrotron light source—the Advanced Light Source (ALS)—in the energy range 50–1300 eV. It was constructed for the characterization of optical elements (mirrors, gratings, multilayers, detectors, etc.) but has capabilities for a wide range of measurements in other fields, in particular materials science and atomic physics. The optical system consists of a monochromator, a reflectometer, a three-mirror order suppressor, and horizontal and vertical focusing mirrors to provide a small spot on the sample. The monochromator is a varied line spacing, plane grating (VLS-PGM) design in which the mechanically ruled grating operates in the converging light from a spherical mirror working at high demagnification. The spherical aberration of this mirror is corrected by the grating line spacing variation, so that the monochromator is essentially aberration-free over its tuning range. Wavelength is scanned by simple rotation of the grating with a fixed exit slit. The small size and stability of the ALS source allows entrance slitless operation, leading to high flux and a spectral resolving power λ/Δλ of around 7000, limited by the ALS vertical source size. The reflectometer has the capability of positioning the sample to 10 μm and setting its angular position to 0.002°. LABVIEW™-based software provides a convenient interface to the user. The reflectometer is separated from the beamline by a differential pump, and can be pumped down to 10−7 torr in 0.5 h. This allows rapid turn-around of materials science samples for measurements which do not require UHV, such as NEXAFS. Auxiliary experimental stations can be mounted behind the reflectometer. Results are shown which demonstrate the performance and operational convenience of the beamline.
We report resonant inelastic x-ray scattering (RIXS) excited by circularly
polarized x-rays on Mn-Zn ferrite at the Mn L2,3-resonances. We demonstrate
that crystal field excitations, as expected for localized systems, dominate the
RIXS spectra and thus their dichroic asymmetry cannot be interpreted in terms
of spin-resolved partial density of states, which has been the standard
approach for RIXS dichroism. We observe large dichroic RIXS at the L2-resonance
which we attribute to the absence of metallic core hole screening in the
insulating Mn-ferrite. On the other hand, reduced L3-RIXS dichroism is
interpreted as an effect of longer scattering time that enables spin-lattice
core hole relaxation via magnons and phonons occurring on a femtosecond time
scale.
The electrical resistivity of Fe-Cr-Fe layers with antiferromagnetic interlayer exchange increases when the magnetizations of the Fe layers are aligned antiparallel. The effect is much stronger than the usual anisotropic magnetoresistance and further increases in structures with more than two Fe layers. It can be explained in terms of spin-flip scattering of conduction electrons caused by the antiparallel alignment of the magnetization.
The x-ray magnetic circular dichroism (XMCD) at the Fe and V 2p edge is measured in Fe/V multilayers. For a V 3 Å/Fe 4.4 Å multilayer, the induced V moment is at least 0.26μB, and it is aligned antiferromagnetically with the Fe layers. The V dichroism signal is revealed to have a complicated structure relative to, e.g., the Fe dichroism signal. We estimate the orbital moment on the V to be 0.13μB, similar to values seen in other ferromagnetic first-row transition metals. Only a lower bound for the V spin moment can be determined (0.13μB), due to the breakdown of the XMCD spin ‘‘sum rule’’ in the case of V.
Single-crystalline Fe(15 ML)/V (1-12 ML) superlattices, epitaxially grown in the (001) direction, have been investigated using magnetization and electrical transport measurements. For all V thicknesses the system exhibits ferromagnetic properties. Results from magnetization and hysteresis measurements with the field applied in different directions confirm that the superlattice is well defined, the interface roughness is small, and the crystallinity of the samples is good. A clear influence of the V thickness, due to strain effects, on the in-plane magnetic anisotropy is found. Resistivity measurements show that the samples exhibit anisotropic magnetoresistive (AMR) properties with a strong dependence of the V thickness on the magnitude of the AMR.
The resonant magnetic x-ray scattering in UAs has been measured from 3.4 to 5.0 keV through the {ital M}{sub III}, {ital M}{sub IV}, and {ital M}{sub V} absorption edges. The data are fit by three dipole oscillators that add coherently. The polarization dependence of nonresonant magnetic scattering was measured at 7.6 keV in the type-IA 2{ital q} phase below {ital T}=63 K. The ratio of the (0,1/2,2){sup {sigma}-{pi}} magnetic reflection to the (0,0,2){sup {sigma}-{sigma}} charge reflection is 1{times}10{sup {minus}9}, and the ratio calculated assuming the free-ion values of {ital L}=6 and {ital S}=3/2 is 1.04{times}10{sup {minus}9}. This is a direct measurement of the strong orbital contribution to the magnetic moment in UAs. In the type-IA phase a tetragonal lattice distortion with {ital c}/{ital a}=1.0002 and a (003){sup {sigma}-{sigma}} charge peak associated with a charge modulation at 2{tau}, where {tau} is the modulation wave vector of the magnetic structure, were observed.
Resonant enhancement of the magnetic x-ray scattering cross section in UAs has been investigated by tuning the incident x-ray energy through the uranium MIV and MV absorption edges. At the MIV edge the intensity for the (0,0,(5/2) magnetic reflection is enhanced by 107 relative to the nonresonant component far above the edge, and is a remarkable 1% of the intensity of the (0,0,2) charge peak. At the MV edge the enhancement is 105. The dramatic enhancement at M edges has been predicted by Hannon et al., and arises from strong electric multipole transitions between atomic core states and the exchange-split Fermi edge states.
X-ray resonant magnetic scattering experiments using linear and circular polarized light were performed at the Ni L2,3 absorption edges on a Ag /Ni multilayer. A superlattice magnetic peak, due to the antiferromagnetic coupling between Ni layers, is evidenced. In the case of a ferromagnetic coupling, large changes in the charge peak (up to 15%) are observed upon reversal of the direction of the magnetic field. The magnetic scattering amplitude is evaluated to 8r0 per nickel atom. Sum rules have been applied for the first time to the energy-dependent magnetic amplitude.
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