Doping and temperature dependence of Mn 3d states in A-site ordered manganites
M. García-Fernández1,2, U. Staub1, Y. Bodenthin1, V. Pomjakushin3, A. Mirone4, J.
Fernández-Rodríguez4, V. Scagnoli4, A. M. Mulders5,6,7, S. M. Lawrence6and E. Pomjakushina8.
1Swiss Light Source, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
2Département de Physique, Université de Fribourg, CH-1700 Fribourg, Switzerland
3Laboratory for Neutron Scattering, Paul Scherrer Institut & ETH Zürich, 5232 Villigen PSI, Switzerland
4European Synchrotron Radiation Facility, BP 220, 38043 Grenoble Cedex 9, France
5School of Physical, Environmental and Mathematical Sciences, UNSW@ADFA, Canberra ACT 2600, Australia
6Department of Imaging and Applied Physics, Curtin University of Technology, Perth, WA 6845, Australia
7The Bragg Institute, Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW 2234, Australia and
8Laboratory for Developement and Methods, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
We present a systematic study of the electronic structure in A-site ordered manganites as function
of doping and temperature. The energy dependencies observed with soft x-ray resonant diffraction
(SXRD) at the Mn L2,3 edges are compared with structural investigations using neutron powder
diffraction as well as with cluster calculations. The crystal structures obtained with neutron powder
diffraction reflect the various orbital and charge ordered phases and show an increase of the Mn-O-
Mn bond angle as function of doping and temperature. Cluster calculations show that the observed
spectral changes in SXRD as a function of doping are more pronounced than expected from an
increase in bandwitdh due to the increase in Mn-O-Mn bond angle, and are best described by holes
that are distributed at the neighbouring oxygen ions. These holes are not directly added to the
Mn 3d shell, but centered at the Mn site. In contrast, the spectral changes in SXRD as function
of temperature are best described by an increase of magnetic correlations. This demonstrates the
strong correlations between orbitals and magnetic moments of the 3d states.
Manganites have attracted a lot of attention in the
past two decades because they show very rich phase di-
agrams with interesting electronic and magnetic prop-
erties that make them challenging to be described from
first principles. For manganites crystallized in the per-
ovskite structure ABO3, the A-site of the perovskite is
coordinated by 12 oxygen sites with A as a trivalent ion
R3+(R ≡Lanthanide). This A-site can be doped with a
divalent cation T2+, normally Ca2+, Ba2+or Sr2+. This
doping causes the Mn ions, that occupy the B-site, to
change its average electronic states from Mn3+to Mn4+.
The B sites are sixfold coordinated and the surround-
ing O2−ions form octahedral cages. Arising from the
strong coupling between the electric, magnetic and struc-
tural properties present in these systems, the physical
and structural properties depend strongly on the doping
content and on the nature of the A-site cation. The most
important of these properties are the appearance of the
colossal magneto resistance (CMR) with the occurrence
of phase separation and unusual spin, charge, lattice and
For the half doped manganite, the generally assumed
ground state consists of the checkerboard CO (charge
order) and OO (orbital order) pattern, which is char-
acterized by the alternation of Mn3+and Mn4+sites
(Mn-centered charge ordering). In the last years other
phases have been proposed to be present in manganites
close to half doping1. Some of those phases present either
bond-centered charge ordering, allowing the existence of
magnetic Zener polaron-type phases; or an intermedi-
ate phase combining site centered CO and bond centered
Figure 1: Perovskite structure of the A-site ordered half doped
manganite TbBaMn2O6. The A-site of the perovskite is oc-
cupied by Tb and Ba ordered in different planes. The Mn
ions are placed at the B-site within the oxygen octahedra.
CO that allows the occurrence of ferroelectricity. Exper-
imentally, Zener polaron phases have also been proposed
for A-site ordered systems of RBaMn2O6, in particular
for R =Y.2However, recent resonant x-ray diffraction
experiments found no inversion symmetry breaking ef-
fects on the Mn sites confirming merely the checkerboard
charge and orbital ordering pattern for different doping
contents and materials studied3. The A-site randomness
(the R3+/T2+solid solution) has a significant influence
on the properties of the system. It increases the magne-
toresistance effect and decreases the charge and orbital
arXiv:1011.2334v1 [cond-mat.str-el] 10 Nov 2010
order temperature TCO/OO. It also makes the charge-
spin-orbital correlation short-ranged4–6. It is therefore
important to study the A-site ordered manganite system
to quantify the effect of the quenched disorder on the
The crystal structure of the cation-ordered material
RBaMn2O6 is of apxapx2ap type with ap ≈ 3.9Å be-
ing the cubic perovskite unit cell parameter (see Figure
1).It was shown that the A-site ordered half doped
system SmBaMn2O6 exhibits a CO/OO transition at
TCO/OO ≈ 360 K and an antiferromagnetic transition
at TN = 250 K followed by a reorientation of the OO
at TCO2 = 200 K5,7. Resonant soft x-ray diffraction
has found an OO of eg electrons with [x2−z2]/[y2−z2]
type7. When the system is hole doped, a linear depen-
dence of the ordering wave vector of the orbital reflection
k = (δx,δx,0) with doping x was found with δ =
in Tb1−xCaxBaMn2O6, while,− →
k = (δy,δy,0) = (1/4,1/4,0) for doping contents
equal and below half doping TbBa1−yLayMn2O63,5. One
possible OO layout for the2/3 doped system is shown in
Our previous resonant x-ray diffraction study showed
that the spectral shape of the orbital reflection exhibits
distinct changes as function of doping at the Mn L2,3
edges3.The characteristic features of the spectra are
similar as for other manganites8–13, but the relative in-
tensities are altered and indicate a progressive alteration
of the electronic Mn states as a function of hole dop-
ing. It was deduced that the anomalous OO melting and
change in (δx, δx, 0) with hole doping are not related to
the structure nor to the magnetic interactions, but rather
due to increased two dimensional character of the orbital
In this paper we continue our investigations of the hole
doped A-site ordered manganites with neutron powder
diffraction, SXRD and cluster calculations in order to
understand the alteration of the electronic Mn states as
function of doping and as function of temperature. The
crystal structures obtained with neutron powder diffrac-
tion reflect the various orbital and charge ordered phases
and show an increase of the Mn-O-Mn bond angle as
function of doping and temperature.
Theoretical simulations of the OO reflections (δ,δ,0)
recorded at the Mn L2,3 edges3,7for the various hole
doping concentrations and as function of temperature are
presented. The cluster calculations consider the effect of
the bandwidth, hole doping and magnetic correlations
and give insight into the electronic ordering of the Mn-O
k was found to be con-
We have investigated polycrystalline samples of
Tb1−xCaxBaMn2O6 with doping contents x=0.05, 0.1,
0.2, 0.33 and 0.4, TbBa1−yLayMn2O6 with y=0.1,
Figure 2: Possible OO ground state in the ab plane for2/3
doping in Tb0.66Ca0.33BaMn2O6. The unit cell is indicated
in the center of the double layer of Mn octahedra and includes
the oxygen ions. The Mn3+ions exhibit alternating x2− z2
and y2− z2orbitals.
640 645650 655660
X-ray Intensity (arb. units)
Figure 3: Energy dependence of the integrated intensity of the
orbital reflection (1/4,1/4, 0) , measured at the Mn L-edges
for polycrystalline Nd0.4Tb0.6BaMn2O6 (solid line) at 26 K
and SmBaMn2O67(striped line) at 120 K. Both sets of data
were collected with π incident radiation, and normalized ans
shifted for clarity.
Nd0.4Tb0.6BaMn2O6. The compounds were synthesized
following the same procedure as in ref7.
structural investigation was performed on compositions
Tb0.66Ca0.33BaMn2O6 and Nd0.4Tb0.6BaMn2O6 using
neutron powder diffraction. The measurements were car-
ried out at the high-resolution diffractometer for thermal
neutrons, HRPT14at the SINQ neutron spallation source
of the PSI, Switzerland. The normal intensity mode of
HRPT was used with the neutron wavelength =1.49 Å.
All the temperature scans were carried out on heating.
The refinements of the crystal structure parameters were
X-ray Intensity (arb. units)
640 642644646648650652654 656658
X-ray Intensity (arb. units)
Figure 4: (color online) (a) Energy dependence of the integrated intensity of the orbital reflection (δx,δx,0), measured at the
Mn L-edges for systems above half doping Tb1−xCaxBaMn2O6 and below half doping TbLayBa1−yMn2O6 in polycrystalline
samples3. The experimental data have been normalized to the intensity at the L3−edge (643 eV) for comparison. (b) Energy
dependence of the integrated intensity of the (1/4,1/4, 0) reflection at half doping of polycrystalline SmBaMn2O6with π incident
radiation, measured at 120 K, 180 K, 235 K and 300 K, renormalized to the intensity at the L3-edge (643 eV)7.
-1 x 104
1 x 104
1.5 x 104
2 x 104
2.5 x 104
3 x 104
Neutron counts (arb.units)
ence plot of the neutron diffraction data for the sample
Tb0.66Ca0.33BaMn2O6 at T=300 K measured at HRPT with
the wavelength λ= 1.49 Å. The rows of ticks show the Bragg
peak positions. The structural parameters are shown in Table
The Rietveld refinement pattern and differ-
performed using FULLPROF15.
Resonant soft x-ray diffraction experiments were per-
formed at the RESOXS16endstation at the SIM beam-
line of the Swiss Light Source of the Paul Scherrer In-
stitut (PSI), Switzerland. Polycrystalline pellets of the
manganite with of 10 mm diameter were glued onto a
copper sample holder mounted on a He flow cryostat
which achieves temperatures between 10 K and 400 K.
Experiments were performed using linear horizontal or
vertical polarized x-rays leading to π or σ incident pho-
ton polarization in the horizontal scattering geometry,
respectively. Two-dimensional data sets were collected
with a commercial Roper Scientific charge-coupled-device
(CCD) camera mounted in vacuum. The sections of the
resonant orbital powder diffraction rings measured with
the CCD camera are integrated along the vertical direc-
tion and fitted with a pseudo-voigt function. This re-
sults in the integrated intensity, the position in 2θ and
the background, which is mainly due to the fluorescence.
The aim of this study is to compare the energy de-
pendencies of the resonant soft x-ray diffraction data
from present A-site ordered manganites (Figures 3 and
4) with theoretical simulations and structural investi-
gations.Since the neutron diffraction investigation of
SmBaMn2O6is hampered by the large neutron absorp-
tion coefficient of Sm, we replace this cation by a mix-
ture of Nd and Tb of the same average radius. The crys-
tal structure of resulting compound Nd0.4Tb0.6BaMn2O6
is determined by neutron powder diffraction without
large absorption. Although the tolerance factor in
SmBaMn2O6 remains to be slightly different than in
Nd0.4Tb0.6BaMn2O6, this produces only a small dif-
ference in the temperature at which the MI transi-
tion takes place.This temperature corresponds to
TCO/OO≈360 K for SmBaMn2O6 and TCO/OO≈400 K
for Nd0.4Tb0.6BaMn2O6. Figure 3 shows the energy de-
pendence of the OO reflection (1/4,1/4,0) measured in
the vicinity of the Mn L2,3 edges for both half doped
compounds. The data is normalized at E=643 eV to
unity and shifted vertically for comparison. The spec-
tral shape of the orbital reflection (1/4,1/4,0) is identical
within the experimental uncertainty. This shows that
the electronic ground state in both compounds can be
assumed to be the same, which makes a direct compar-
ison between structural data obtained by neutrons and
the spectroscopic x-ray data feasible.
The crystal structure of half doped R1−xTxMnO3
manganites for which R and T ions are randomly dis-
tributed (solid solution), such as La0.5Ca0.5MnO3, can
be described in orthorhombic symmetry at high temper-
structure is Pnma, which contains only one symmetry
equivalent Mn site and therefore does not describe long-
range CO at Mn sites17.Below TCO/OO, the crystal
structure is refined in a monoclinic P21/m symmetry
2?2apx2apx?2ap superstructure, with two inequiva-
and orbital ordering18. The structures of several other
half-doped manganites have subsequently been fitted us-
ing the same model19–21.
As concerns the A-site ordered manganites like
TbBaMn2O6, their high temperature crystal structure
is described by the orthorhombic space group Cmmm.
Similarly to solid solutions R1−xTxMnO3, all Mn sites are
equivalent22. At TCO/OO=473 K, the system undergoes
a crystal structure transition from orthorhombic to mon-
oclinic P21/m, associated with a diversification of Mn
valences or formation of Zener polarons2,22. However,
the major monoclinic P21/m superstructure reflections
were observed to be very weak in our measured powder
patterns. Therefore the neutron diffraction data were re-
fined with orthorhombic (Cmmm) crystal symmetry and
2apx2apx2apcrystal structure15for all temperatures and
doping contents. It was observed that when the stoi-
chiometry of the system changes, the diffraction pattern
changes too. However, this changes do not result in a
detectable new crystal symmetry, but can simply be de-
scribed by the atomic motions and changes of the unit
cell parameters. The diffraction pattern at 300 K and the
refinement plot for the Tb0.66Ca0.33BaMn2O6sample are
shown in Figure 5. The structure parameters obtained
from this refinement are shown in Table 1.
The MI transition is a first order transition leading
to the coexistence of two phases in the vicinity of the
transition temperature. The temperature dependence of
the unit cell parameters and volume are shown in Fig-
ure 6 for the half doped compound Nd0.4Tb0.6BaMn2O6
and2/3 doped compound Tb0.66Ca0.33BaMn2O6.
lattice constants undergo dramatic changes. Two transi-
tions can be distinguished in the temperature evolution
of the unit cell parameters and the volume, one in the
vicinity of TCO/OO∼410 K, (Figure 6) and the other in
the vicinity of TCO2∼210 K .
When increasing the temperature above TCO/OO =
410 K (see figure 6a) in the half doped material, the
unit cell parameters a and c show sharp positive jumps
at TCO/OO of 0.13% and 0.81% respectively, while b
drops by -1.05%. Those anisotropic changes of the crys-
tal unit cell result in an abrupt drop of the unit cell
volume at TCO/OO by -0.11%.
lapse was also observed at the MI transition in A-site
ordered HoBaCo2O5.523. In this cobaltite, the volume
?T ≥ TCO/OO
?. The space group of this crystal
lent Mn sites in the unit cell, consistent with a charge
A similar volume col-
collapse of the unit cell has been associated to the occur-
rence of orbital order of the Co3+ions. In the vicinity of
TCO2= 210 K, where a restacking of the OO has been
observed5,7, a small drop in the unit cell volume is ob-
Similar behaviour is observed close to the MI transi-
tion in2/3 doped Tb0.66Ca0.33BaMn2O6(see figure 6b).
The unit cell parameters a and c show a sharp increase
at TCO/OOof 0.97% and 0.30% respectively, while b de-
creases by -1.41%. The anisotropic changes of the crystal
unit cell result in an abrupt drop of the unit cell vol-
ume at TCO/OOof -0.16%. Surprisingly, the changes of
the lattice constants a and b are larger than in the half
doped system. In contrast, in the vicinity of TCO2 =
210 K, a decrease in unit cell volume as in the case of
Nd0.4Tb0.6BaMn2O6is absent, yet a change in slope is
noted. This agrees with the fact that OO restacking does
not occur for the hole doped compounds. We note that
additional reflections are observed for T < 200K, indica-
tive for antiferromagnetic ordering with TN< TCO2.
In summary, a similar contraction of the crystal struc-
ture is seen for all hole doped systems near the MI transi-
tion at TCO/OO, whereas the changes in crystal structure
near TCO2are different.
Previously the energy dependence of the orbital re-
flection (δx,δx,0), where [δx= δ (x)], for x > 0 and
(1/4,1/4,0) for y = 0.1, in the vicinity of the Mn L2,3edges
was recorded for different doping contents close to half
doping (ref.3reproduced in Figure 3.a). The spectra are
normalized to their maxima at the Mn L3edge. It shows
that there is a distinct trend in the shape of the spectra
with doping, i.e. some features of the energy become
broader or more intense compared with others.
ses differences indicate a variation of the electronic Mn
states. In a simple view such a change is not expected.
When the doping is increased beyond half doping, the
holes are disposed as far as possible from each other, giv-
ing rise to the linear behavior of q versus doping3. In this
case, the local structure around the Mn3+ions (consid-
ering the nearest neighbors only) is not directly affected
In Figure 3.b the energy dependence of the OO reflec-
tion (1/4,1/4,0) measured in the vicinity of the Mn L2,3
edges for the half doped material SmBaMn2O6is shown
for temperatures between 120 K and 300 K normalized at
E=643 eV to unity. In a previous study of this half doped
compound it was shown that the energy dependences do
not change dramatically with temperature7in contrast to
what was observed in La0.5Sr1.5MnO424. In the latter,
the different features of the energy scan were shown to
follow different trends as function of temperature, which
was interpreted in terms of different order parameters of
orbital order and Jahn-Teller distortion. Features labeled
C and F correspond to Jahn Teller distortion, features A
0.247(1) 0.2563(6) 0.49(5)
Table I: Structure parameters in Tb0.66Ca0.33BaMn2O6 [space group Cmmm (No.65)]. The data are refined from the powder
neutron diffraction pattern measured at HRPT/SINQ with wavelength λ=1.49Å (Fig. 5). The Bragg reliability factor is
RBragg=11.3% and the conventional reliability factors are Rwp=8.95, Rexp=4.70 and χ2=3.62.
Figure 6: (a) (above) Unit cell parameters as a function of temperature for Nd0.4Tb0.6BaMn2O6.
volume with temperature for Nd0.4Tb0.6BaMn2O6.
Tb0.66Ca0.33BaMn2O6. (below) Variation of volume with temperature for Tb0.66Ca0.33BaMn2O63. L.T. stands for low tem-
perature phase and H.T. for high temperature phase.
(below) Variation of
(b) (above) Unit cell parameters as a function of temperature for
and B mostly to the OO. Although this clear different
behavior is absent for SmBaMn2O6, small but distinct
dissimilarities of different type can also be seen between
energy dependences measured at different temperatures.
Features D, E and F become more intense upon heat-
ing, while feature C broadens in comparison to features
A and B. The evolution of the spectra as a function of
temperature follows a similar trend as the ones observed
as a function of doping.
The L2,3edges are sensitive to the local environment
of the scattering atom. Doping and temperature modify
the local environment structurally and/or electronically.
Concerning structural changes, in the Cmmm space
group and with the 2apx2apx2ap cell we have five dif-
ferent oxygen sites leading to several Mn-O-Mn angles,
and different oxygen positions (see Table I) . To simplify
the comparison we merge those angles obtained from the
structural refinements to obtain an average Mn-O-Mn
bond angle (Fig. 7a). As can be seen in Figure 7a, the
average Mn-O-Mn angle increases for increasing doping.
The work of J.L. García-Muñoz et al.25indicates that
this corresponds to an increase in bandwidth. We plot in
Figure 7b the analogous result obtained as a function of
increasing temperature, showing a similar trend.
Average Mn-O-Mn angle (deg)
Average Mn-O-Mn angle (deg)
Figure 7: (a) Evolution of the average angle Mn-O-Mn as function of doping content in Tb1−xCaxBaMn2O6. The inset
shows the unit cell of the high-temperature structure of Tb1−xCaxBaMn2O6 in which the Mn-O1-Mn angle is visualized as a
tilt between the two neighbouring oxygen octahedra. (b) Evolution of the average angle between Mn-O-Mn as a function of
temperature in Nd0.4Tb0.6BaMn2O6.
640 642644646648 650652654656658
X-ray Intensity (arb. units)
Figure 8: Change in spectral shape of the (δx, δx, 0) reflection
as a function of εp which results in a variation of the hole
density at the oxygen sites.
The change of the average angle as a function of doping
is about twice as large compared to the one upon temper-
ature. The error bars versus temperature obtained from
statistical error propagation of the individual errors are
very large compared to the scattering of the data points.
This indicates that the obtained individual bond angles
are significantly correlated. Therefore the accuracy of
the average angle is much better than the plotted error
bars obtained from statistical error propagation.
Another interesting point is the relation between
the orbital restacking transition at half-doping and the
anomalous orbital melting for the2/3 doping. Both tran-
sitions, which have been previously observed in soft x-
ray resonant scattering measurements, can also be de-
tected in the temperature dependence of the unit cell vol-
ume of both compounds (Figure 6). For the half-doping
case, at low temperatures the orbital planes (Mn3+) are
aligned along the c-axis, whereas above TCO2, the stack-
ing of the orbital planes is pair wise shifted in the plane.
This orbital stacking transition is sketched in the inset
of Figure 6a. For the2/3 doping, at low temperatures we
could assume again a ferro-type staking along the c-axis,
but above TCO2, differently to the previous case, there’s
much more freedom to stack the individual planes along
the c-axis. Shifting a plane perpendicularly to c by one
perovskite unit cell, in one direction or its opposite, does
not lead to the same result (see inset Figure 6b). The
extended possibilities of having different stacking along
the c-axis, lead to many states which differ very little in
energy. This allows having a thermally excited switching
between the different stacking representing a dynamical
sliding of the planes and that is equivalent to a correlated
motion of electrons. This decoupling of ordered planes
leads then to the slight volume increase above the onset
of the dynamics that is visible in Figure 6b. Moreover,
such dynamical sliding will also be expected to affect the
correlation in the ab plane. The change of ordering pe-
riod in this dynamical regime might then reflect a slightly
smaller doping than the one expected from the exact Ca
content. The OO unit cell is free to relax in the plane
due the diminishing coupling along the c axis for increas-
ing temperatures. Such sliding planes might possibly be
related to the recently proposed sliding character of the
Calculations to describe the spectral shape of the
orbital reflection have been done using the model of
reference27. This model describes, in second quantiza-
tion, a small cluster consisting of a central Mn3+site
and the first neighbouring shells of O and Mn4+sites.
The interaction term T1of equation 2 of reference27has
been modified in order to obtain an orbital ordering of
the egelectron of x2−y2kind in the ground state which
corresponds to the presumed ordering for our physical
system7. Here we like to note that the calculation of the
structure factor does not depend directly on the ordering
wave vector change for increased doping, as the scatter-
ing factors are calculated in the cluster code. It merely
is reflected by the phase difference of π of the two orbital
oriented sites?x2−z2/y2−z2?in the resonant x-ray struc-
with the 2p orbitals of the neighbouring oxygen ions and
T1is given by:
ture factor. The T1term hybridizes the Mn 3d orbitals
where the symbols o and d are second quantization
operators for the oxygen and central Mn orbitals respec-
tively. The y axis is in the crystal c direction. The value
g = 0.7 from reference27is used. In the original model
the g factor multiplies only the o†
voring a 3x2− r2orbital ordering. Here, the g factor
multiplies also the o†
x2− y2type OO.
The effect of change in the bandwidth on the OO spec-
tra can be simulated by changing the t prefactor in the
T1term and/or in the T2one (equation 3 of reference27)
which hybridizes the 2p oxygen orbitals with the Mn4+
ones. By varying t proportionally to the cosine of the
Mn-O-Mn angle from Figure 7 we did not observe no-
ticeable effects. An angle variations of the order of 1%
has a too small effect on the bandwidth. This indicates
that the change in bandwidth does not directly reflect
the changes of the spectral shape of the orbital reflection.
Correspondingly, it might be a secondary effect caused by
the doping and not relevant in the understanding of the
electronic changes versus doping.
The direct effect of doping on the electronic structure
has been simulated in the hypothesis of hole density con-
centrated on oxygen sites. To do so we have varied the
εpparameter in equation 4 of reference27to take into ac-
count the electrostatic interaction of holes on the oxygen
orbitals. εprepresents the bare energy of the oxygen p
orbitals, and is deduced from the charge transfer energy
∆, which is defined as the energy to transfer an electron
from the oxygen onto a bare Mn atom (in the absence
of hybridization). Lowering εpreflects therefore a trans-
fer (or condensation) of holes at the oxygen. The oxygen
UppHubbard term being estimated to 5 eV (reference27),
an increase in x of 0.4 corresponds to a decrease in εpof
1 eV in the case of holes going to in-plane oxygen sites.
Figure 8 shows the change in spectral shape of the
(δx,δx,0) reflection as a function of εp. A decrease of the
energy of the oxygen 2p orbitals leads to an increase of
the L2 edge and of feature C. The agreement between
x,σdx2,σ term, thus fa-
y,σdy2,σ hopping operator, favoring
X-ray intensity (arb. units)
Figure 9: Theoretical simulation of the effect of changing the
magnetic correlations on the energy dependence of the orbital
reflection (δx, δx, 0) in the vicinity of Mn L2,3-edge.
these calculations in Figure 8 and the experimental re-
sult obtained as function of hole doping (Figure 3a) is
We have also tested the hypothesis of hole density in-
crease at the Mn ion site by changing the bare energy
of the Mn d orbitals εd. These simulations of increased
holes at the Mn sites show an opposite trend in the energy
dependencies compared to those calculated for increased
holes at the oxygen sites. We conclude therefore that the
holes are introduced in the oxygen 2p shell rather than
in the Mn 3d shell. The fact that the hole doping leads
to a linear dispersion of the orbital reflection with a2/3
doping being represented by a tripling of the unit cell,
indicates that the holes are not centered at the oxygen
nor at the bond, but are centered around the Mn ions.
In other words, it suggests that each neighboring oxygen
gets the same fraction of the hole so that the center of
mass stays at the Mn site, but is not directly affecting
the 3d electron count.
This view is consistent with very recent investigation
of the Mn Kβfluorescence spectroscopy28and theoretical
calculations based on LDA+U of the electronic structure
of manganites29. They find that the holes are introduced
at the oxygen sites, forming an egsymmetry orbital, leak-
ing charge to the former Mn4+sites. This results in a
reduced charge transfer between the former Mn3+and
Mn4+sites, representing a strong covalent character of
the Mn-O sublattice.
The temperature dependence of the energy dependence
of the OO reflection at half doping cannot be explained
by an increase in hole density at the oxygen site. Such
increase of holes is expected to increase the intensity at
the oxygen K edge, as there are more empty states ac-
cessible as intermediate states in the resonant process.
In addition the intensity at the Mn L3main edge (643
eV) is expected to decrease, as the total charge is tem-
perature independent. This is in contrast with the ob-
served temperature dependence of the OO intensity at
the oxygen K edge and Mn L3edge respectively, which
are equal3. Moreover, the observed increase in Mn-O-
Mn angle, which remains small, does not support the
observed increase in relative intensity at the L2 edge.
This suggest that the temperature effect on the spectral
shape of the orbital reflection is probably more complex.
It has been shown previously that the magnetic moment
direction as well as spin correlations changes the spectral
shape of the orbital reflection27,30.
To investigate the influence of spin correlations on the
spectral shape at half doping we consider the lowest cal-
culated energy eigenstates, in particular the first five
eigenstates. They are contained within an energy range
of the order of 10 meVs and correspond to different ori-
entations of the central Mn spin S. They originate from
the polarising term H227which acts on the eg orbitals
of the cluster Mn4+external ions. This polarising term
accounts, for the on-site mean-field exchange with the t2g
orbitals. These outer Mn t2gorbitals, are absent from the
model, and are represented by this mean field term. The
inclusion of the external t2gstates in the model would be
computationally very expensive.
Therefore we have performed two calculations. The
first calculation, named LT, has been performed as de-
scribed above inducing magnetic correlations H2 as in
reference27at low temperature. The scattering factors
from the first five eigenstates are averaged with weights
decreasing versus eigenenergy.
For the second calculation, named HT, we reduce the
slope of the weights dependence versus eigen-energy and
at the same time we reduce the polarising term by di-
viding h by two in H227. The parameter h is a direct
measure of the spin correlations and reducing it, mim-
ics the effect of temperature induced spin disorder and
the consequent reduction of the Mn-Mn magnetic cor-
relation. The factors that we use describe qualitatively
a temperature increase from 120 K at LT to 300 K at
HT. The result of these calculations is shown in Figure
9. The spectral shape changes mainly by an increase of
intensity at the L2edge compared to the L3edge. Our
simulation reproduces the main trend in spectral shape
giving further support of the importance of magnetic cor-
relations in the description of the electronic properties of
these manganites systems.
The hole doping and temperature dependence of A-
site ordered manganites has been studied with neutron
powder diffraction. In addition, we compare the reso-
nant soft x-ray powder diffraction spectra to cluster cal-
culations. The orbital order of the Mn3+3d states ex-
hibits electronic changes as function of hole doping and
as function of temperature. We have explored the origin
of these electronic changes.
served in the orbital reflection with resonant diffraction
at the Mn L2,3edges resemble similarity as function of
hole doping and temperature. Our theoretical modeling
demonstrates that the relative intensity at the L2 edge
increases, both for increased hole density at the oxygen
and for induced spin disorder as function of temperature.
In case of hole doping, the resonant spectra are well de-
scribed with additional holes residing in the oxygen 2p
shell yet centered around the Mn3+ions. In contrast,
the electronic changes observed as function of tempera-
ture are more likely caused by spin correlations.
The spectral changes ob-
The structural study found a volume increase at the
anomalous orbital melting transition temperature for the
2/3 doping system, interpreted in terms of a decoupling
and an onset of a dynamical sliding of two dimensional
OO planes.However, including these changes of the
bandwidth in the model calculations do not lead to ob-
servable changes of the calculated spectra, and therefore
indicate that the bandwidth change as a function of dop-
ing and temperature is a secondary effect.
The experiments were performed and at the X11MA
beamline of the SLS at the SINQ of the Paul Scher-
rer Institut, Villigen, Switzerland and we want to thank
their staff for their excellent support. We acknowledge
the financial support of the following institutions, the
Swiss National Science Foundation, the NCCR MaNEP
project, the “Access to Major Research Facilities Pro-
gramme” which is a component of the “International Sci-
ence Linkages Programme” established under the Aus-
tralian Government’s innovation statement, “Backing
Australia’s Ability” NSFCH and the Gobierno del Prin-
cipado de Asturias for the financial support of a Postdoc-
toral grant from Plan de Ciencia, Tecnologia e Innovacion
(PCTI) de Asturias 2006–2009.
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