DSpace at VNU: Ti-doped A-site deficient lanthanum manganites: Local structure and properties

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Journal of Magnetism and Magnetic Materials 300 (2006) e175–e178
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Ti-doped A-site deficient lanthanum manganites:
Local structure and properties
Alexander N. Ulyanova,Ã, Dong-Seok Yangb, Kyu-Won Leec, Jean-Marc Greneched,
Nguyen Chaue, Seong-Cho Yua
a
Department of Physics, Chungbuk National University, Cheongju 361-763, Korea
Physics Division, School of Science Education, Chungbuk National University, Cheongju 361-763, Korea
c
Korea Research Institute of Standards and Science, Yusong, Taejon 305-600, Korea
d
Laboratoire de Physique de L’Etat Condense´, UMR CNRS 6087, Universite´ du Maine, 72085 Le Mans, Cedex 9, France
e
Center for Materials Science, National University of Hanoi, 334 Nguyen Trai, Hanoi, Vietnam
b

Available online 16 November 2005

Abstract
A study of La0.6Sr0.4ÀxMnTixO3 (x ¼ 0:0, 0.05, 0.1, 0.15, and 0.2) manganites with the Ti in B( ¼ Mn)-position and vacancies in
A( ¼ La, Sr)-site is presented. The manganites belonged to the rhombohedral phase and small amount of Mn3O4 oxide was observed
with increase of Ti content. X-ray adsorption fine structure (XAFS) analysis showed an appearance of Mn2+ ions in perovskite cell and
tremendous change of local structure. We suppose that the change of local structure was mainly caused by the appearance of Mn ions in
the A-positions and partially by the formation of vacancies in the above position with the increase of x-value. Curie temperature, T C ,
decreased drastically with x: T C ðx ¼ 0Þ ¼ 355 K and, T C ðx ¼ 0:05Þ ¼ 185 K. Further increase of Ti content changed the low-temperature
magnetic state from the ferromagnetic to spin/cluster glass state. Effects of destruction of the eg electron pathway and change of local
structure on Curie temperature, caused by the Ti doping, is discussed.

r 2005 Elsevier B.V. All rights reserved.
PACS: 75.30.Àm; 75.30.Kz; 61.10.Ht
Keywords: Manganites; A- and B-site substitution and deficiency; Curie temperature; Local structure

Doped Ln1ÀxRxMnO3 manganese oxides are under the
extensive study due to the colossal magnetoresistivity
(CMR) effect observed at temperatures close to ferromagnetic ordering temperature, T C (Ln is a rare earth, Y; R is
an alkaline earth) [1]. The CMR phenomenon was initially
explained by the double exchange (DE) interaction
between Mn3+ and Mn4+ ions via oxygen 2p orbitals [2].
According to the DE model, transfer of itinerant eg
electrons between the neighboring Mn ions (local t2g spins)
through the O2À ion results in a ferromagnetic interaction
due to the on-site Hund’s coupling. The strength of the DE
interaction is estimated by the transfer integral, teff . The
electronic bandwidth, W , is proportional to the teff and
depends on Mn–O–Mn bond angles and Mn–O bond
ÃCorresponding author. Tel.: +82 43 271 8146; fax: +82 43 274 7811.

E-mail address: (A.N. Ulyanov).
0304-8853/$ - see front matter r 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jmmm.2005.10.177

distances in MnO6 octahedron through the overlap
integrals between the Mn cation 3d orbitals and the O
anion 2p orbitals. An empirical formula [3]
W ¼ W 0 cosðy=2Þ=d 3:5

(1)

was used to describe the dependence (y ¼ pÀ
/Mn–O–MnS and d is an average /Mn–OS bond
length).
Very rich phase diagram and interesting properties of
CMR materials are attributed to the A( ¼ Ln, R)- and
B( ¼ Mn, transition metal)-site substitution of manganites.
Deficiency of atoms in A-position in the so-called
La1ÀxMnO3 self-doped manganites also causes the CMR
effect because of the appearance of the mixed Mn3+-Mn4+
valence state [4,5]. The unusual result was obtained in Ref.
[5]: the occurrence of Mn atoms in A-position was
concluded by neutron diffraction when studying the A-site


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A.N. Ulyanov et al. / Journal of Magnetism and Magnetic Materials 300 (2006) e175–e178

deficient La1ÀxMnO3 manganites. To elucidate this question, we present a study of lanthanum manganites with the
simultaneous B-site substitution and creation of vacancies
in A-position.
La0.6Sr0.4ÀxMnTixO3+d
(LSMTO)
compositions
(x ¼ 0:0, 0.05, 0.1, 0.15, and 0.2) were synthesized by
solid-state reaction method. X-ray absorption fine structure (XAFS) experiments were performed at the 7C1 beam
line of the Pohang Light Source (PLS) in Korea. PLS
operated with electron energy of 2.5 GeV and the
maximum current of 230 mA. X-rays were monochromatized by the Si(1 1 1) double-crystal monochromator with
the energy resolution, DE/E ¼ 2 Â 10À4. Higher harmonics
were removed by a 15 percent detuning of the crystal.

XAFS spectra were measured near the Mn K-edge
(6540 eV) in a fluorescence mode at room temperature.
Magnetization measurements were carried out with the
SQUID (Quantum Design MPMSXL) magnetometer.
According to X-ray CuKa (XRD) analysis the samples
belonged to rhombohedral (R3¯ c) phase and contained a
small amount of Mn3O4 oxide, which increased with x
(see Fig. 1).
Temperature dependencies of magnetization in the field
of 50 Oe (field cooled, warming rate) are presented in
Fig. 2. The x ¼ 0 and 0.05 compositions were ferromagnetic, and the compounds with the higher x content were in

Mn3O4

La0.6Sr0.4-xMnTixO3+δ

Intensity (arb.units)

x=0.2

x=0.15

x=0.1

x=0.05

x=0

20

40

60

80

2Θ (degree)
Fig. 1. XRD patterns of La0.6Sr0.4ÀxMnTixO3+d manganites.

18
16
14
50 Oe,
warming rate

12
Magnetization (emu/g)

e176

10
8
6
4
2
0
-2
0

100

200
300
Temperature (K)

400

Fig. 2. Magnetization vs. temperature dependencies for the
La0.6Sr0.4ÀxMnTixO3+d manganites (x ¼ 0, 0.05, 0.1, 0.15, and 0.2 from
the right to the left).

spin(cluster)-glass-like state at low temperature. The spinglass-like behavior of x ¼ 0:1 composition was reported in
Ref. [6]. The careful analysis of the character of low
magnetic state for (xX0:10) samples will be published
elsewhere.
Curie temperature decreased dramatically with small
increase of x-value (see Fig. 2): T C ðx ¼ 0Þ ¼ 355 K and,
T C ðx ¼ 0:05Þ ¼ 185 K. The T C change was stronger than
that observed in La0.7Ca0.3Mn1ÀxTixO3 [7] and
La0.7Sr0.3Mn1ÀxTixO3 [8] manganites. It was probably
due to (i) a non-uniform(multisite) distribution of Mn
ions, (ii) appearance of Mn2+ ions, and deficiencies of ions
in the A-position of perovskite cell in addition to the
removing of pathway for the itinerant eg electrons and
change of local structure caused by the Ti occupation in the
B-site. To carefully elucidate this question, the XAFS
analysis was carried out. XAFS represents extended X-ray
absorption fine structure (EXAFS) and X-ray absorption
near edge structure (XANES) analysis, which give information about the local structure around a central atom and
the electronic configuration (valence) of the core Mn

cations, respectively. XANES spectra were obtained
directly by the normalization of absorption spectra, and
the Fourier transformations of the EXAFS spectra, which
give the rough picture of radial distribution of atoms
around the Mn ion in perovskite cell, were obtained by
regular way described in Ref. [9].
XANES (Fig. 3), EXAFS (are not shown) and Fourier
transform of EXAFS spectra (Fig. 4) showed a continuous
change with x. XANES spectra shifted to lower energy and
essentially broadened with x. It is important to emphasize


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A.N. Ulyanov et al. / Journal of Magnetism and Magnetic Materials 300 (2006) e175–e178

1.4

Absorption spectra (arb.units)

1.2
MnO
1.0
0.8
0.6
0.4
0.2
0.0
-0.2

6.54

6.55
E (keV)

6.56

Fig. 3. XANES spectra of La0.6Sr0.4ÀxMnTixO3+d manganites (x ¼ 0:0;
0.05; 0.1; 0.15; and 0.2, from the right to the left) and MnO oxide.

|Fourier transform| (arb.units)

x=0.0

x=0.05

x=0.1

x=0.15

x=0.2

0

2

4
R (Å)

6

8

Fig. 4. Fourier transform of EXAFS spectra for La0.6Sr0.4ÀxMnTixO3+d
compositions.

e177

that in the case of the La1ÀxCaxMnO3 compositions
[10,11], the XANES spectra showed almost the same shape
and only shifted parallel to each other. The shift of the
absorption edge from the lower to higher energy with x was
caused by the change of average Mn valence from 3+ (in
LaMnO3) to 4+ (in CaMnO3). The main absorption for
the Mn3+ ion (in LaMnO3) was observed at the interval
from 6550 to 6556 eV. The absorption for the Mn2+ ion in
MnO oxide was observed at lower energies than that for
the Mn3+ ion in LaMnO3.
The very different picture has been observed in our study
(see Fig. 3, where the LSMTO and MnO XANES spectra
are presented). Really, the spectrum for the La0.6Sr0.4MnO3 composition showed almost the same shape and
position as that in La0.7Ca0.3MnO3 one [10]. But, a small
amount of Ti (x ¼ 0:05) only caused considerable changes
in XANES spectra: (i) the spectra became broader and low
energy ‘‘tail’’ appeared; (ii) the ‘‘tail’’ became wider (spread
to lower energy) and more intensive with x; (iii) visible Xray absorption appeared just at the 6.547 keV for the x ¼
0:05 sample and increased with x. The changes of XANES
spectra probably originated from (a) the occurrence of
divalent Mn ions, which was manifested by the appearance
of X-ray absorption at energies lower than 6.550 keV, and
(b) a nonuniform distribution of Mn ions—partial occupation of A-position by the Mn ions—as indicated by the

broadening of XANES spectra. The nonuniform(multisite)
distribution of Mn ions in perovskite cell was also
confirmed by the Fourier transform of EXAFS spectra
(Fig. 4). Namely, it is well established [9], that the
regularity in appearance of high-intensity peaks, as for
the x ¼ 0 samples, clearly evidences for uniform distribution of Mn atoms in lattice, and a complete disappearance
of third and fourth peaks with x, as for the xX0:10
compositions, is an evidence of nonuniform distribution of
Mn ions in the perovskite cell. We suppose thus that Mn2+
occupy the A-position, and Mn3+,4+ ions, as usually,
occupy the B-site. Really, in the La0.6Sr0.4ÀxMnTixO3+d
compositions one concludes to a deficiency of atoms in Aposition of perovskite cell, and an excess of Mn and Ti
atoms, which almost always occupy the B-site. The Aposition is occupied by La3+ and Sr2+ ions with ionic radii
1.216 and 1.31 A˚, respectively (all ionic radii are taken
according to Shannon [12]). The most preferable ions, which
can occupy the A-position among the Mn2+( ¼ 0.83 A˚),
Mn3+( ¼ 0.645 A˚), and Mn4+( ¼ 0.53 A˚) ones, are the
Mn2+ ion as the largest one. We have to note that if the
Ti4+( ¼ 0.605 A˚) ions occupy the A-position there will not
be so strong change in the Fourier spectra. There will be
only a weak change in intensity of second peak, which is
caused by the backscattering of electrons by the atoms,
located in the A-positions (see, for example, the case of
La0.7Ca0.3ÀxBaxMnO3 manganites in Ref. [13]). So, it is
finally possible to describe the compositions as
(La0.6Sr0.4ÀxMny)(Mn1ÀyÀzTix)O3+d1 +(z/3)Mn3O4, where
y and z depend on x; the atoms in first and second brackets
occupy the A- and B-positions, respectively. The very similar

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A.N. Ulyanov et al. / Journal of Magnetism and Magnetic Materials 300 (2006) e175–e178

LayMnO3+(z/3)Mn3O4 (y % 0:9) segregation in the range
0.9XLa/MnX0.7 was reported [4] when studying the
La1ÀxMnO3+d compositions.
The change in Curie temperature and magnetization of
the B-site substituted manganites mainly originates from
the weakening of the DE interaction because the breaking
of the pathway for the itinerant eg electrons, caused by the
difference in electron configurations between the Mn3+,
Mn4+ ions and transition metal ions-change of W 0 in (1)(E-factor); and by the structural S-factor: change of
/Mn–OS bond distances and /Mn–O–MnS bond angles
because the difference in Mn and dopant size ionic radii
(see, e.g., [14] and references therein). The observed T C and
magnetization decrease in La0.6Sr0.4ÀxMnTixO3+d was
stronger than that observed in La0.7Ca0.3Mn1ÀxTixO3 [7]
and La0.7Sr0.3Mn1ÀxTixO3 [8]. The stronger T C decrease is
obviously caused by the occurrence of Mn2+ ions and
deficiency of atoms in A-position of perovskite cell in
addition to the E- and S-factors.
In summary, the segregation of La0.6Sr0.4ÀxMny
Mn1ÀyÀzTixO3+d1 phase and fallout of Mn3O4
oxide with x increase was observed. The x increase caused
the Mn2+ ions appearance and deficiency of atoms in Aposition, which together with the substitution of Ti for Mn
in B-site caused the strong decrease in magnetization and
Curie temperature, and change the character of low
temperature magnetic state of high x value samples.

The Research at Chungbuk National University was
supported by the Korean Research Foundation Grant

(KRF—2003-005-C00018). A.N. Ulyanov was supported
by Brain Pool Program of the Korean Ministry of
Educations. The authors are indebted to H.D. Quang for
the ac susceptibility measurements.

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