Pressure-dependent electronic structures in multiferroic DyMnO(3): A combined lifetime-broadening-suppressed x-ray absorption spectroscopy and ab initio electronic structure study.
ABSTRACT Variations in the electronic structure and structural distortion in multiferroic DyMnO(3) were probed by synchrotron x-ray diffraction, lifetime-broadening-suppressed x-ray absorption spectroscopy (XAS), and ab initio electronic structure calculations. The refined x-ray diffraction data enabled an observation of a diminished local Jahn-Teller distortion of Mn sites within MnO(6) octahedra in DyMnO(3) on applying the hydrostatic pressure. The intensity of the white line in Mn K-edge x-ray absorption spectra of DyMnO(3) progressively increased with the increasing pressure. With the increasing hydrostatic pressure, the absorption threshold of an Mn K-edge spectra of DyMnO(3) shifted toward a greater energy, whereas the pre-edge line slightly shifted to a smaller energy. We provide the spectral evidence for the pressure-induced bandwidth broadening for manganites. The intensity enhancement of the white line in Mn K-edge spectra is attributed to a diminished Jahn-Teller distortion of MnO(6) octahedra in compressed DyMnO(3). A comparison of the pressure-dependent XAS spectra with the ab initio electronic structure calculations and full calculations of multiple scattering using the code FDMNES shows the satisfactory agreement between experimental and calculated Mn K-edge spectra.
- SourceAvailable from: Zhengcai Xia[Show abstract] [Hide abstract]
ABSTRACT: The mutual controls of ferroelectricity and magnetism are stepping towards practical applications proposed for quite a few promising devices in which multiferroic thin films are involved. Although ferroelectricity stemming from specific spiral spin ordering has been reported in highly distorted bulk perovskite manganites, the existence of magnetically induced ferroelectricity in the corresponding thin films remains an unresolved issue, which unfortunately halts this step. In this work, we report magnetically induced electric polarization and its remarkable response to magnetic field (an enhancement of ~800% upon a field of 2 Tesla at 2 K) in DyMnO3 thin films grown on Nb-SrTiO3 substrates. Accompanying with the large polarization enhancement, the ferroelectric coercivity corresponding to the magnetic chirality switching field is significantly increased. A picture based on coupled multicomponent magnetic structures is proposed to understand these features. Moreover, different magnetic anisotropy related to strain-suppressed GdFeO3-type distortion and Jahn-Teller effect is identified in the films.Scientific Reports 01/2013; 3:3374. · 5.08 Impact Factor
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ABSTRACT: The GdFeO3-type lattice distortion and consequent ferroelectric behavior in polycrystalline DyMnO3 with different grain sizes are studied by means of the Rietveld refinement of the X-ray diffraction at room temperature and ferroelectric measurements at low temperature. As evidenced by the variation in the in-plane MnOMn bond angle and the ferroelectric polarization, the distorted crystal structure and ferroelectric behavior of DyMnO3 can be effectively modulated by varying grain size. This work sheds light on the size effect in type-II multiferroic manganites.Physica B Condensed Matter 09/2012; 407(18):3736–3739. · 1.28 Impact Factor
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ABSTRACT: The pressure-induced phase transition of the hexagonal manganite ErMnO3 has been investigated using the synchrotron x-ray diffraction technique up to 57.6 GPa in a diamond anvil cell. The hexagonal structure exhibits anisotropic compression behavior. The bulk modulus (B0) is 168(3) GPa with B0′ = 4.0 (fixed). At room temperature, ErMnO3 undergoes a hexagonal-to-orthorhombic phase transition at ∼20.2 GPa, but coexists with the orthorhombic phase up to the highest pressure of 57.6 GPa. When laser-heated to 1500-2000 K, the hexagonal ErMnO3 transforms to a denser orthorhombic perovskite structure completely at ∼17 GPa, accompanied by ∼11% volume reduction. The distortion and tilts of the octahedra MnO6 in the orthorhombic structure decrease with increasing pressure. The bulk modulus of the orthorhombic structure is 214(4) GPa with B0′ = 4.0 (fixed), larger than that of the hexagonal structure. The orthorhombic structure ErMnO3 is stable at least up to ∼45 GPa and can be quenched.Journal of Applied Physics 12/2012; 112(11). · 2.19 Impact Factor
Pressure-dependent electronic structures in multiferroic DyMnO3:
A combined lifetime-broadening-suppressed x-ray absorption
spectroscopy and ab initio electronic structure study
J. M. Chen,1,a?,b?J. M. Lee,1,2T. L. Chou,1S. A. Chen,1S. W. Huang,1,2H. T. Jeng,3,a?,c?
K. T. Lu,1T. H. Chen,1Y. C. Liang,1S. W. Chen,1W. T. Chuang,1H.-S. Sheu,1
N. Hiraoka,1H. Ishii,1K. D. Tsuei,1Eugene Huang,4C. M. Lin,5and T. J. Yang2
1National Synchrotron Radiation Research Center (NSRRC), Hsinchu 30076, Taiwan, Republic of China
2Department of Electrophysics, National Chiao Tung University, Hsinchu 30010, Taiwan, Republic
3Institute of Physics, Academia Sinica, Taipei 11529, Taiwan, Republic of China
4Center for General Education, Chung Chou Institute of Technology, Changhua County 510, Taiwan,
Republic of China
5Department of Applied Science, National Hsinchu University of Education, Hsinchu 30014, Taiwan,
Republic of China
?Received 18 March 2010; accepted 26 August 2010; published online 19 October 2010?
Variations in the electronic structure and structural distortion in multiferroic DyMnO3were probed
by synchrotron x-ray diffraction, lifetime-broadening-suppressed x-ray absorption spectroscopy
?XAS?, and ab initio electronic structure calculations. The refined x-ray diffraction data enabled an
observation of a diminished local Jahn–Teller distortion of Mn sites within MnO6octahedra in
DyMnO3on applying the hydrostatic pressure. The intensity of the white line in Mn K-edge x-ray
absorption spectra of DyMnO3progressively increased with the increasing pressure. With the
increasing hydrostatic pressure, the absorption threshold of an Mn K-edge spectra of DyMnO3
shifted toward a greater energy, whereas the pre-edge line slightly shifted to a smaller energy. We
provide the spectral evidence for the pressure-induced bandwidth broadening for manganites. The
intensity enhancement of the white line in Mn K-edge spectra is attributed to a diminished Jahn–
Tellerdistortion of MnO6
pressure-dependent XAS spectra with the ab initio electronic structure calculations and full
calculations of multiple scattering using the code FDMNES shows the satisfactory agreement
between experimental and calculated Mn K-edge spectra. © 2010 American Institute of Physics.
DyMnO3. A comparison ofthe
Perovskite manganites RMnO3and hole-doped mangan-
ites of composition R1−xAxMnO3?rare-earth ions R and
alkaline-earth ions A? exhibit fascinating physical properties,
such as charge and orbital ordering,1–3metal-insulator
multiferroicity.17–24In many such phenomena, the electronic
properties are related intimately to the crystal lattice, through
a complicated interplay between the crystal lattice, spin,
charge, and orbital degrees of freedom.25–29In particular,
magnetoelectrics, in which magnetism and ferroelectricity
coexist and are mutually coupled have attracted renewed at-
tention because of both their intrinsic scientific interest and
prospective applications in novel magnetoelectric and
magneto-optical devices. The magnetoelectric effect signifies
an electric polarization generated with a magnetic field or a
magnetization generated with an electric field in a material.
Multiferroicity has been observed in such manganites as
TbMnO3, DyMnO3, and TbMn2O5.17–19
Figure 1 shows the crystal structure of orthorhombic
DyMnO3. The perovskite DyMnO3structure contains the
corner-sharing MnO6octahedra with the Mn ion at their cen-
ters and Dy occupying holes between the octahedra. The
small radius of the Dy ion in RMnO3produces a cooperative
buckling and tilting of the corner-shared MnO6octahedra
known as GdFeO3distortions. At an ambient pressure and
temperature, the perovskite DyMnO3structure distorts to
orthorhombic Pbnm symmetry. The MnO6octahedron in
DyMnO3is highly distorted, and tilted with an average Mn–
O–Mn bond angle of ?145° in the plane to be compared
with a value of ?155° in LaMnO3. The Jahn–Teller ?JT?
distortion of the Mn3+O6octahedra in DyMnO3produces
Mn–O bonds in three pairs: one Mn–O1 for apical bonds
along the c axis, and two Mn–O2 for equatorial bonds in the
ab plane. In the basal ab plane, long Mn–O2?l? ?2.22 Å? and
short Mn–O2?s? bonds ?1.89 Å? alternate.
DyMnO3shows an incommensurate crystallographic su-
perstructure below the Néel temperature ?TN=39 K? corre-
sponding to a sinusoidal antiferromagnetic ordering of the
a?Authors to whom correspondence should be addressed.
b?Electronic mail: email@example.com.
c?Electronic mail: firstname.lastname@example.org
THE JOURNAL OF CHEMICAL PHYSICS 133, 154510 ?2010?
0021-9606/2010/133?15?/154510/7/$30.00© 2010 American Institute of Physics
Mn moments along the b axis. The transition ?T?18 K? to a
noncollinear spiral magnetic ordering in which inversion
symmetry is broken is accompanied with a large spontaneous
electric polarization along the c axis ??2?10−3C m−2?.30
The appearance of ferroelectricity at the transition into the
spiral structure of RMnO3with R=Tb, Dy, and Gd was ex-
plained microscopically in terms of a spin supercurrent ac-
cording to Pe=?eij??Si?Sj?, in which appear electric po-
larization Pe, magnetic moments Siand Sj, the unit vector eij
connecting sites i and j, and factor ?, which is proportional
to the transfer integral.31The magnetoelectric effect is thus
correlated closely with the noncollinear spin configurations
induced by a significant cooperative Jahn–Teller distortion of
MnO6octahedra and a large octahedral tilt angle.32The JT
distortion and tilt angle of MnO6octahedra in DyMnO3can
become modified when smaller ions or divalent cations are
incorporated into the rare-earth sites or when hydrostatic
pressure is applied.33In addition to the induced structural
disorders, doping with divalent cations or monovalent cat-
ions into rare-earth sites in RMnO3generally complicates the
electronic structure, producing mixed valence states or
oxygen-deficient states.33,34External pressure is therefore an
ideal tool to tune the extent of the JT distortion in rare-earth
The insulator-metal transition ?IMT? of rare-earth man-
ganites mediated with an external hydrostatic pressure is
reported.35,36The variation of electron bandwidth under hy-
drostatic pressure is proposed to serve as a driving force to
induce the IMT of rare-earth manganites,35but the spectral
evidence for a pressure-induced bandwidth variation of man-
ganites is still sparse. X-ray absorption spectra ?XAS? with
chemical selectivity provide insight complementary to dif-
fraction measurements into the local environment around an
absorber atom of a material under pressure. The K-edge ab-
sorption spectra of transition-metal oxides reveal a strong
dependence on the charge distribution and symmetry distor-
tions of the probed site in a material,37–39but 1s core-hole
lifetime broadening ??1.15 eV? in absorption precludes ob-
taining the spectra at high resolution, particularly the pre-
edge features in the K-edge absorption spectra of transition-
In this work, we applied techniques derived from a reso-
nant inelastic x-ray scattering called the lifetime broadening
suppressed x-ray absorption spectroscopy in the partial fluo-
rescence yield.40The K-edge XAS spectra at high resolution,
particularly in the pre-edge region, provide an accurate spec-
tral information about the electronic structure and local
structure of a material under pressure. The dependence of the
orthorhombic Pbnm perovskite structure of RMnO3?R=Dy,
Gd, and Tb? on temperature and magnetic field is
known,17–19but the effect of hydrostatic pressure on highly
distorted multiferroic DyMnO3is less investigated. In this
work, we probed the variations of electronic structure and
structural distortion in orthorhombic DyMnO3under external
hydrostatic pressure using combined XAS and x-ray diffrac-
tion ?XRD? techniques. The pressure-dependent Mn K-edge
XAS spectra were compared with the results of the ab initio
electronic structure calculations and full multiple-scattering
calculations using the code FDMNES.41
Polycrystalline DyMnO3was synthesized with a conven-
tional citrate-gel process. Dy2O3and MnO in stoichiometric
proportions were dissolved in aqueous solutions of citric and
nitric acids. The solution was heated at 95 °C until a spongy
gel was formed, and then heated at a higher temperature to
produce dark-colored ashes. These ground ashes were first
calcinated at 600 °C in air to remove organic residues, and
then further calcinated 950 °C in air for 12 h to obtain ad-
equate crystallinity. Orthorhombic DyMnO3of satisfactory
quality was used for the subsequent high pressure experi-
The dependence of an Mn K-edge x-ray absorption on
pressure was measured at the Taiwan inelastic x-ray scatter-
ing beamline BL12XU in SPring-8.42The synchrotron radia-
tion from an undulator was made monochromatic with a
Si?111? double-crystal monochromator and focused to a spot
?16?20 ?m2full width at half maximum ?FWHM? in a
diamond-anvil pressure cell using two mirrors in a
Kilpatrick–Baez ?KB? geometry. The emitted x-ray fluores-
cence was analyzed with a spectrometer comprising a syn-
chronously moving, spherically bent Si ?440? analyzer and a
photon-counting detector on the 1-m-armed Rowland circle.
The overall resolution, which is evaluated from the quasi-
elastic scattering from the sample, had a FWHM of 0.9 eV.
The incident energy was calibrated with the known Mn
K-edge absorption inflection point at 6539 eV of an Mn foil.
A sample DyMnO3as a finely grained powder was loaded
into a hole ?diameter 100 ?m? of a Be gasket mounted on a
Mao-Bell type diamond anvil cell ?culet size 550 ?m?. Sili-
cone oil served as a medium to transmit pressure. All mea-
surements were performed at room temperature. The applied
FIG. 1. Crystal structure of DyMnO3.
154510-2Chen et al.J. Chem. Phys. 133, 154510 ?2010?
hydrostatic pressure was averaged at multiple points through
the line shift of the ruby luminescence before and after each
The pressure-dependent x-ray diffraction was measured
at the beamline BL01C2 of National Synchrotron Radiation
Research Center ?NSRRC? in Taiwan. The incident x rays
?wavelength 0.4959 Å, 25 keV? were generated from the
superconducting wavelength-shifter beamline with a Si?111?
double-crystal monochromator. The DyMnO3 powder as
grown was filled into the pinhole ?diameter of 235 ?m? of a
stainless-steel gasket with an Au powder as a pressure indi-
cator and a mixture of methanol-ethanol-water ?16:3:1? as a
pressure-transmitting medium in a diamond anvil cell ?Mao-
Bell type, culet size 550 ?m?. An Au powder standard was
used to determine precisely the wavelength and the distance
from the sample to the detector. The XRD pattern was re-
corded with a MAR345 imaging plate ?exposure duration
typically of ?20 min?. The one-dimensional XRD pattern
was converted with program FIT2D. The x-ray diffraction
data was structurally refined with the Rietveld method as
implemented in the general structure analysis system soft-
III. RESULTS AND DISCUSSION
In Fig. 2, the representative x-ray diffraction patterns of
orthorhombic DyMnO3over the hydrostatic pressure range
ambient to ?30 GPa at room temperature were reproduced.
Because of the decreased size of particles and the pressure
gradients in the sample upon applying an external pressure,
the x-ray diffraction peaks exhibit a gradual broadening with
an increasing pressure, as shown in Fig. 2.43In the entire
range of pressure up to 30 GPa, the crystal structure of
DyMnO3retains its initial Pbnm symmetry.
To deduce the complete crystal structure including lattice
parameters and atomic positions, we refined the x-ray pow-
der diffraction data with the Rietveld method up to ?8 GPa.
Figure 3 shows typical XRD patterns recorded at P=1.2 and
7.8 GPa with their corresponding Rietveld refinement. The
experimental XRD data and their Rietveld refinement agreed
satisfactorily according to the small magnitudes of the re-
siduals. The structural parameters of DyMnO3calculated
from the diffraction data for selected pressures are given in
Table I. Experimental XRD data and their Rietveld refine-
ment agreed satisfactorily according to the small values of
reliability parameters Rwp, Rp, and ?2shown in Table I. The
values of structural parameters obtained at ambient pressure
agree satisfactorily with those in the literature.44
To illuminate the detailed pressure-induced structural
distortion, we demonstrate in Fig. 4 the pressure dependence
of Mn–O distances including the apical distance Mn–O1 and
equatorial distances Mn–O2, and the in-plane Mn–O2–Mn
bond angle. These values are deduced from the structural
parameters in Table I. As noted from Fig. 4?a?, the short
equatorial bond Mn–O2?s? and the apical distance Mn–O1
remain virtually constant for a hydrostatic pressure less than
8 GPa, which is the largest effect being a shortening of the
long equatorial bond Mn–O2?l?.
This condition indicates that the Jahn–Teller distortion of
FIG. 2. Representative x-ray diffraction patterns of orthorhombic DyMnO3
for hydrostatic pressure in a range ambient to ?30 GPa.
FIG. 3. X-ray diffraction patterns for DyMnO3?circles? with their Rietveld
refinement ?solid line? and residuals for pressures ?a? P=1.2 GPa and ?b?
P=7.9 GPa. The first row of the vertical marks at an individual pressure
corresponds to calculated peak positions of DyMnO3and the second row to
the Au reference as a pressure indicator.
Pressure-dependent x-ray absorption of DyMnO3
J. Chem. Phys. 133, 154510 ?2010?
the MnO6octahedra in DyMnO3becomes suppressed upon
applying an external hydrostatic pressure. A similar observa-
tion is reported for LaMnO3under hydrostatic pressure.45As
noted from Fig. 4?b?, the Mn–O2–Mn bond angle increases
monotonically with an increasing hydrostatic pressure. Ac-
cordingly, the in-plane Mn–O2–Mn tilt angle of two adjacent
MnO6octahedra ?i.e., ?180°—Mn–O2–Mn bond angle?/2?
decreases monotonically with an increasing pressure. From
the observation in Fig. 4, we infer a gradual symmetrization
of the MnO6JT-distorted octahedra in DyMnO3with an in-
In Fig. 5, the high-resolution Mn K-edge XAS spectra of
polycrystalline DyMnO3collected at various pressures up to
?22 GPa were reproduced. The spectra were obtained as a
partial fluorescence yield with the spectrometer energy fixed
at the maximum of the Mn K?13line. The Mn K-edge XAS
spectrum of DyMnO3at ambient pressure contains two well
resolved prepeaks in the pre-edge region ?labeled P1 and P2?
and an asymmetric white line ?labeled B? with a shoulder on
the side of small energy, and a broad peak ?labeled C? at a
greater photon energy.
As noted from Fig. 5, the Mn K-edge XAS spectra of
DyMnO3at various pressures exhibit only a slight modifica-
tion, implying that the local atomic environment about Mn in
DyMnO3is not greatly altered under an external hydrostatic
pressure up to ?22 GPa, which is consistent with the
present XRD results. With an increasing external pressure,
the intensity of the white line labeled B ?6555–6565 eV? in
the Mn K-edge spectra of DyMnO3increased progressively,
whereas the shoulder of the white line became gradually sup-
pressed, as shown in the insets of Fig. 5. At a greater pres-
sure, the shape of the white line gradually became symmet-
ric. With an increasing hydrostatic pressure, the absorption
threshold labeled A and the broad peak labeled C in the Mn
K-edge spectra of DyMnO3continuously shifted toward
greater energy, whereas the pre-edge peak labeled P1 gradu-
ally shifted to smaller energy. Pre-edge peak P1 in Fig. 5 at
P=22 GPa shifted to a smaller energy, ?0.3 eV, which is
relative to that at P=0.3 GPa, as shown in the insets of
To ensure an accurate assignment of the pre-edge fea-
tures labeled P1 and P2 in Fig. 4, we performed band-
structure calculations for orthorhombic DyMnO3 in an
A-type antiferromagnetic structure based on the experimen-
tal lattice parameters, as listed in Table I with 20 atoms in the
TABLE I. Room-temperature structural parameters for DyMnO3?Pbnm? at
four selected pressures calculated from the x-ray diffraction data.
01.2 4.7 7.9
FIG. 4. Pressure dependence of ?a? Mn–O distances including apical dis-
tance Mn–O1 and equatorial distance Mn–O2, and ?b? Mn–O2–Mn bond
angle of distorted MnO6octahedra in DyMnO3.
FIG. 5. High-resolution Mn K-edge XAS spectra, recorded by the partial
fluorescence yield, of polycrystalline DyMnO3at various pressures up to
?22 GPa. The insets show an enlarged pre-edge region and near the
154510-4Chen et al.J. Chem. Phys. 133, 154510 ?2010?
unit cell. The band-structure calculations were performed us-
ing the full-potential projected augmented wave method
implemented in the Vienna ab initio simulation package
within the generalized gradient approximation plus on-site
Coulomb interaction U ?GGA+U? scheme.46,47In the GGA
+U calculations, the Coulomb energy U=5.0 eV and ex-
change parameter J=0.87 eV for Mn 3d electrons were
used.48A ?7?7?5? Monkhorst–Pack grid in the first
Brillouin-zone which corresponds to 79 k-points in the irre-
ducible part of the Brillouin-zone and the cutoff energy of
400 eV for the plane waves are chosen for present calcula-
tions. The convergence of the k-point sampling and cutoff
energy is confirmed by comparing the results with those
from a ?8?8?6? k-point mesh ?92 k-points? with cutoff
energy of 500 eV.
In the perovskite manganites DyMnO3, the Mn3+ion has
a d4configuration. In an octahedral symmetry, the Mn 3d
levels split into three lower-lying t2g?dxy, dyz, and dzx? and
two higher-lying egorbitals. The Mn3+ion has a high-spin
configuration, with three electrons occupying the three t2g
orbitals and one electron occupying the doubly degenerate eg
orbitals as t2g
DyMnO3perovskites is removed by a cooperative Jahn–
Teller distortion. The egdoublet is split further into two sub-
Figure 6?a? displays the partial density of states of five-
fold Mn 3d states for DyMnO3. There is an indirect gap
1. The degeneracy of the egorbital in
1↑ and eg
2↑ resulting from a strong Jahn–Teller dis-
between the JT-split Mn eg
GGA+U calculations, the occupied eg
dy2−z2 orbitals, respectively, in one coplanar Mn ion, whereas
they exhibit predominantly d3y2−r2 and dx2−z2 character, re-
spectively, for the other coplanar Mn ion. A strong orbital
polarization in the egband for DyMnO3with a staggered
d3x2−r2/d3y2−r2-type orbital ordering pattern in the ab plane is
For the spin-down channel, one eg↓ band ?d3z2−r2? is
mixed with the t2g↓ bands at 3–4 eV above Ef, whereas the
other eg↓ band ?dx2−y2? is located ?4.5 eV above Ef. The
Mn–O2?l? site projected predominantly along the b axis,
Mn–O2?s? site projected predominantly along the a axis.
The splitting of the eg↑ orbitals in the t2g
figuration of the Mn3+ions is therefore closely related to the
JT distortion and the orbital ordering within the MnO6octa-
hedra in DyMnO3. Figure 6?b? displays the partial density of
states of fivefold Mn 3d states for DyMnO3at P=1.2 and
7.9 GPa. The structural parameters of DyMnO3at pressures
1.2 and 7.9 GPa are listed in Table I. The electronic band of
the eg↑ orbitals and t2g↓ in DyMnO3under pressure is
slightly broadened and shifted to lower energy.
The 1s→3d transitions are generally considered to be
weakly allowed either through a quadrupole interaction or
via hybridization of the Mn 3d states with 4p states.49Based
on the band structure calculations, P1 in Fig. 5 is ascribed to
transitions of Mn 1s core electrons into unoccupied,
majority-spin Mn eg↑ states hybridized with neighboring Mn
4p states. P2 in Fig. 5 is assigned as a superposition of tran-
sitions into empty, minority-spin t2g↓ and eg↓ states hybrid-
ized with neighboring 4p states. The white line, labeled B in
Fig. 5, is attributed to transitions from Mn 1s to Mn 4p
states. Feature C in Fig. 5 gains intensity from the multiple-
scattering contribution of MnO6surrounded by eight Dy.
As shown in Fig. 4, the pressure effect is most pro-
nounced for the long equatorial distance Mn–O2?l? that re-
lates to the larger compressibility along the b axis under
pressure. The compressive anisotropy of MnO6octahedra in
DyMnO3 upon applying hydrostatic pressure leads to a
modified density of states. The electronic bandwidth of eg↑
orbitals is a key parameter to drive the insulator-metal tran-
sition of manganites.35,45The bandwidth of the eg↑ orbitals
in manganites is closely related to the overlap between the
Mn 3d and O 2p orbitals, and is highly correlated with the
local atomic structure of MnO6octahedra including the equa-
torial bond distance Mn–O2 and the in-plane Mn–O2–Mn tilt
angle.50The equatorial Mn–O2 distance and Mn–O2–Mn tilt
angle decreased under an external pressure, as confirmed by
the present XRD measurements, enhance the hybridization
of the Mn 3d and O 2p orbitals and are expected to broaden
the electronic band of eg↑ orbitals in DyMnO3.47The pre-
edge line P1 originating from transitions of Mn 1s core elec-
trons to unoccupied Mn 3d?eg↑? states is accordingly gradu-
ally shifted toward smaller energy when a hydrostatic
pressure is applied, consistent with the present GGA+U cal-
culations shown in Fig. 6?b?.
1↑ and eg
2↑ bands. Based on the
1↑ and unoccupied
2↑ bands ??2 eV above Ef? are dominated by d3x2−r2 and
1↑ orbitals of Mn3+ions are located at the long
FIG. 6. ?a? Partial densities of states of Mn projected onto fivefold 3d
orbitals at ambient pressure and ?b? partial density of states of Mn 3d states
for DyMnO3at P=1.2 and 7.9 GPa for an hypothetical A-type antiferromag-
netic structure of orthorhombic DyMnO3calculated with the GGA+U
method. The parameters in these calculations are described in the text. For
each panel the upper half denotes the majority and the lower half the mi-
nority spin states. The energy zero is at the Fermi energy ?Ef?.
Pressure-dependent x-ray absorption of DyMnO3
J. Chem. Phys. 133, 154510 ?2010?
Polarization-dependent Mn K-edge x-ray absorption
spectra of RMnO3?R=Tb, Dy? single crystals were previ-
ously observed to exhibit a notable anisotropy along three
crystallographic directions, E?a, E?b, and E?c, particularly
for the white-line region.49The white line in the polarized
Mn K-edge spectrum of DyMnO3for the E?b polarization
lies at an energy ?2.4 eV smaller than for polarizations E?a
and E?c, corresponding to a highly anisotropic Mn–O2
bonding within the ab plane and weak covalency along the b
axis in RMnO3?R=Tb, Dy?.49The origin of this energy dif-
ference is attributed to a Jahn–Teller distortion and orbital
ordering of MnO6octahedra in RMnO3?R=Tb, Dy?.51A
significant energy separation for the maximum of the white
line of the polarized Mn K-edge spectrum along E?b relative
to E?a and E?c produces an asymmetric profile of the white
line, with a shoulder on the side of small energy of the Mn
K-edge spectrum for polycrystalline DyMnO3at ambient
When the long equatorial bond Mn–O2?l? projected pre-
dominantly along the b axis is greatly shortened with an
increasing hydrostatic pressure and approaches the length of
the short equatorial bond Mn–O2?s? projected predomi-
nantly along the a axis, as evident in Fig. 4?a?, the absorption
edge of the Mn K-edge spectrum for E?b of DyMnO3gradu-
ally shifts to greater energy. The separation for the maximum
of the white line of the Mn K-edge spectra between E?b and
E?a of DyMnO3decreases because of a diminished JT dis-
tortion of DyMnO3upon applying an external hydrostatic
pressure. An increased overlap between the E?b spectrum
and the E?a spectrum under hydrostatic pressure conse-
quently generates an increased intensity of the white line in
the Mn K-edge spectra of DyMnO3,52as supported by the
gradually suppressed shoulder of white line with pressure in
With the FDMNES code, we performed the Mn K-edge
XAS calculations on DyMnO3based on the structural param-
eters at various pressures in Table I. In the present XAS
simulation, a muffin-tin ?MT? full-multiple-scattering ?FMS?
approach was applied with a cluster radius R=5 Å. We
found that a spherical cluster of radius 5 Å satisfactorily
reproduces all features of the absorption spectrum. The FMS
calculations were performed using the MT potential con-
structed from 10% overlapped MT spheres of the specified
radii. Figure 7 shows simulated Mn K-edge XAS spectra of
DyMnO3with varied hydrostatic pressures. The intensity of
the white line clearly increases with an increasing pressure.
As shown in the insets of Fig. 7 with an increasing hydro-
static pressure, the absorption threshold of simulated Mn
K-edge spectra of DyMnO3shifts toward greater energy,
whereas the pre-edge peak shifts to smaller energy. The ex-
perimental and calculated Mn K-edge spectra agree satisfac-
Pressure-induced variations of electronic structure and
DyMnO3were probed on combining x-ray powder diffrac-
tion and lifetime-broadening-suppressed x-ray absorption
spectroscopy recorded in the partial fluorescence yield. With
an increasing external pressure, the short equatorial bond dis-
tance Mn–O2?s? and the Mn–O1 apical distance remained
virtually constant for a pressure less than 8 GPa, the largest
effect being a shortening of the long equatorial bond
Mn–O2?l?. The in-plane Mn–O2–Mn tilt angle of two adja-
cent MnO6octahedra decreased monotonically upon apply-
ing hydrostatic pressure. Based on these XRD results, a local
JT distortion of Mn sites within MnO6octahedra in DyMnO3
becomes suppressed with an increasing hydrostatic pressure.
The intensity of the white line in Mn K-edge x-ray absorp-
tion spectra of DyMnO3increased progressively with an in-
creasing pressure, whereas the shoulder of the white line was
gradually suppressed. With an increasing hydrostatic pres-
sure, the absorption threshold of Mn K-edge spectra of
DyMnO3shifted toward greater energy, whereas the pre-
edge line shifted slightly to smaller energy. The intensity
enhancement of the white line of Mn K-edge spectra is at-
tributed to a diminished Jahn–Teller distortion of MnO6oc-
tahedra in DyMnO3when a hydrostatic pressure is applied.
We provide spectral evidence for the pressure-induced band
broadening for manganites. The comparison of XAS data
with ab initio electronic structure calculations and full
multiple-scattering calculations using code FDMNES shows
satisfactory agreement between experimental and calculated
Mn K-edge spectra.
We thank the NSRRC staff for their technical support.
This research is supported by the NSRRC and the National
Science Council of the Republic of China under Grant Nos.
NSC 96-2113-M-213-007 and NSC 98-2112-M-001-021.
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Pressure-dependent x-ray absorption of DyMnO3
J. Chem. Phys. 133, 154510 ?2010?