Magnetic and transport properties driven by lattice strain in La₀.₇Ca₀.₃MnO₃/BaTiO₃ and La₀.₇Sr₀.₃MnO₃/BaTiO₃ bilayered films
The microstructure and the magnetic and transport properties of La₀.₇Ca₀.₃MnO₃ and La₀.₇Sr₀.₃MnO₃ films deposited on a BaTiO₃ layer (LCMO/BTO and LSMO/BTO) and on a LaAlO₃ (001) single crystal (LCMO/LAO and LSMO/LAO) by rf-magnetron sputtering using «soft» (or powder) targets are investigated....
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| Zitieren: | Magnetic and transport properties driven by lattice strain in La₀.₇Ca₀.₃MnO₃/BaTiO₃ and La₀.₇Sr₀.₃MnO₃/BaTiO₃ bilayered films / V.G. Prokhorov, V.A. Komashko, G.G. Kaminsky, K.K. Yu, S.J. Jun, S.Y. Park, J.S. Park, Y.P. Lee, V.L. Svetchnikov, // Fizika Nizkikh Temperatur. — 2007. — Т. 33, № 1. — С. 78-87. — Бібліогр.: 50 назв. — англ. |
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irk-123456789-1275032017-12-24T03:03:14Z Magnetic and transport properties driven by lattice strain in La₀.₇Ca₀.₃MnO₃/BaTiO₃ and La₀.₇Sr₀.₃MnO₃/BaTiO₃ bilayered films Prokhorov, V.G. Komashko, V.A. Kaminsky, G.G. Yu, K.K. Jun, S.J. Park, S.Y. Park, J.S. Lee, Y.P. Svetchnikov, V.L. Низкотемпеpатуpный магнетизм The microstructure and the magnetic and transport properties of La₀.₇Ca₀.₃MnO₃ and La₀.₇Sr₀.₃MnO₃ films deposited on a BaTiO₃ layer (LCMO/BTO and LSMO/BTO) and on a LaAlO₃ (001) single crystal (LCMO/LAO and LSMO/LAO) by rf-magnetron sputtering using «soft» (or powder) targets are investigated. The films grown on BTO demonstrate biaxial tensile in-plane and compressive out-of-plane strains, while the films grown on LAO, in contrast, manifest compressive in-plane and tensile out-of-plane strains. The films with biaxial tensile in-plane lattice strain undergo the magnetic transition at a higher temperature than that for the biaxial compressive case. This argues that the Mn–O–Mn bond-angle variation, controlled by the lattice strain, plays a more important role in the formation of the spin ordering than the attendant modification of the Mn–O bond length. It was shown that the magnetic inhomogeneity, expressed by a significant difference between the field-cooled and zero-field-cooled temperature-dependent magnetization, has a metallurgical rather than an electronic nature, and is controlled by the crystal lattice distortion and the microstructure defects. The observed enhancement of the magnetoresistance effect in the LSMO/BTO bilayer at room temperature make this object greatly beneficial in the development of new hybrid ferromagnetic/ferroelectric devices. 2007 Article Magnetic and transport properties driven by lattice strain in La₀.₇Ca₀.₃MnO₃/BaTiO₃ and La₀.₇Sr₀.₃MnO₃/BaTiO₃ bilayered films / V.G. Prokhorov, V.A. Komashko, G.G. Kaminsky, K.K. Yu, S.J. Jun, S.Y. Park, J.S. Park, Y.P. Lee, V.L. Svetchnikov, // Fizika Nizkikh Temperatur. — 2007. — Т. 33, № 1. — С. 78-87. — Бібліогр.: 50 назв. — англ. 0132-6414 PACS: 71.30.+h, 75.47.Gk, 75.47.Lx http://dspace.nbuv.gov.ua/handle/123456789/127503 en Физика низких температур Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України |
| institution |
Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| collection |
DSpace DC |
| language |
English |
| topic |
Низкотемпеpатуpный магнетизм Низкотемпеpатуpный магнетизм |
| spellingShingle |
Низкотемпеpатуpный магнетизм Низкотемпеpатуpный магнетизм Prokhorov, V.G. Komashko, V.A. Kaminsky, G.G. Yu, K.K. Jun, S.J. Park, S.Y. Park, J.S. Lee, Y.P. Svetchnikov, V.L. Magnetic and transport properties driven by lattice strain in La₀.₇Ca₀.₃MnO₃/BaTiO₃ and La₀.₇Sr₀.₃MnO₃/BaTiO₃ bilayered films Физика низких температур |
| description |
The microstructure and the magnetic and transport properties of La₀.₇Ca₀.₃MnO₃ and
La₀.₇Sr₀.₃MnO₃ films deposited on a BaTiO₃ layer (LCMO/BTO and LSMO/BTO) and on a
LaAlO₃ (001) single crystal (LCMO/LAO and LSMO/LAO) by rf-magnetron sputtering using
«soft» (or powder) targets are investigated. The films grown on BTO demonstrate biaxial tensile
in-plane and compressive out-of-plane strains, while the films grown on LAO, in contrast, manifest
compressive in-plane and tensile out-of-plane strains. The films with biaxial tensile in-plane
lattice strain undergo the magnetic transition at a higher temperature than that for the biaxial
compressive case. This argues that the Mn–O–Mn bond-angle variation, controlled by the lattice
strain, plays a more important role in the formation of the spin ordering than the attendant modification
of the Mn–O bond length. It was shown that the magnetic inhomogeneity, expressed by a
significant difference between the field-cooled and zero-field-cooled temperature-dependent magnetization,
has a metallurgical rather than an electronic nature, and is controlled by the crystal
lattice distortion and the microstructure defects. The observed enhancement of the magnetoresistance
effect in the LSMO/BTO bilayer at room temperature make this object greatly beneficial
in the development of new hybrid ferromagnetic/ferroelectric devices. |
| format |
Article |
| author |
Prokhorov, V.G. Komashko, V.A. Kaminsky, G.G. Yu, K.K. Jun, S.J. Park, S.Y. Park, J.S. Lee, Y.P. Svetchnikov, V.L. |
| author_facet |
Prokhorov, V.G. Komashko, V.A. Kaminsky, G.G. Yu, K.K. Jun, S.J. Park, S.Y. Park, J.S. Lee, Y.P. Svetchnikov, V.L. |
| author_sort |
Prokhorov, V.G. |
| title |
Magnetic and transport properties driven by lattice strain in La₀.₇Ca₀.₃MnO₃/BaTiO₃ and La₀.₇Sr₀.₃MnO₃/BaTiO₃ bilayered films |
| title_short |
Magnetic and transport properties driven by lattice strain in La₀.₇Ca₀.₃MnO₃/BaTiO₃ and La₀.₇Sr₀.₃MnO₃/BaTiO₃ bilayered films |
| title_full |
Magnetic and transport properties driven by lattice strain in La₀.₇Ca₀.₃MnO₃/BaTiO₃ and La₀.₇Sr₀.₃MnO₃/BaTiO₃ bilayered films |
| title_fullStr |
Magnetic and transport properties driven by lattice strain in La₀.₇Ca₀.₃MnO₃/BaTiO₃ and La₀.₇Sr₀.₃MnO₃/BaTiO₃ bilayered films |
| title_full_unstemmed |
Magnetic and transport properties driven by lattice strain in La₀.₇Ca₀.₃MnO₃/BaTiO₃ and La₀.₇Sr₀.₃MnO₃/BaTiO₃ bilayered films |
| title_sort |
magnetic and transport properties driven by lattice strain in la₀.₇ca₀.₃mno₃/batio₃ and la₀.₇sr₀.₃mno₃/batio₃ bilayered films |
| publisher |
Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України |
| publishDate |
2007 |
| topic_facet |
Низкотемпеpатуpный магнетизм |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/127503 |
| citation_txt |
Magnetic and transport properties driven by lattice strain in La₀.₇Ca₀.₃MnO₃/BaTiO₃ and La₀.₇Sr₀.₃MnO₃/BaTiO₃ bilayered films / V.G. Prokhorov, V.A. Komashko, G.G. Kaminsky, K.K. Yu, S.J. Jun, S.Y. Park, J.S. Park, Y.P. Lee, V.L. Svetchnikov, // Fizika Nizkikh Temperatur. — 2007. — Т. 33, № 1. — С. 78-87. — Бібліогр.: 50 назв. — англ. |
| series |
Физика низких температур |
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| fulltext |
Fizika Nizkikh Temperatur, 2007, v. 33, No. 1, p. 78–87
Magnetic and transport properties driven by lattice strain
in La0.7Ca0.3MnO3/BaTiO3 and La0.7Sr0.3MnO3/BaTiO3
bilayered films
V.G. Prokhorov, V.A. Komashko, and G.G. Kaminsky
Institute of Metal Physics of the National Academy of Sciences of Ukraine, Kiev 03142, Ukraine
E-mail: pvg@imp.kiev.ua
K.K. Yu, S.J. Jun, S.Y. Park, J.S. Park, and Y.P. Lee
q-PSI and Department of Physics, Hanyang University, Seoul 133-791, Korea
V.L. Svetchnikov
National Center for HREM, TU Delft, 2628AL, The Netherlands
Received February 3, 2006, revised March 13, 2006
The microstructure and the magnetic and transport properties of La07. Ca03. MnO3 and
La07. Sr03. MnO3 films deposited on a BaTiO3 layer (LCMO/BTO and LSMO/BTO) and on a
LaAlO3 (001) single crystal (LCMO/LAO and LSMO/LAO) by rf-magnetron sputtering using
«soft» (or powder) targets are investigated. The films grown on BTO demonstrate biaxial tensile
in-plane and compressive out-of-plane strains, while the films grown on LAO, in contrast, mani-
fest compressive in-plane and tensile out-of-plane strains. The films with biaxial tensile in-plane
lattice strain undergo the magnetic transition at a higher temperature than that for the biaxial
compressive case. This argues that the Mn–O–Mn bond-angle variation, controlled by the lattice
strain, plays a more important role in the formation of the spin ordering than the attendant modifi-
cation of the Mn–O bond length. It was shown that the magnetic inhomogeneity, expressed by a
significant difference between the field-cooled and zero-field-cooled temperature-dependent mag-
netization, has a metallurgical rather than an electronic nature, and is controlled by the crystal
lattice distortion and the microstructure defects. The observed enhancement of the magneto-
resistance effect in the LSMO/BTO bilayer at room temperature make this object greatly benefi-
cial in the development of new hybrid ferromagnetic/ferroelectric devices.
PACS: 71.30.+h, 75.47.Gk, 75.47.Lx
Keywords: magnetotransport properties, ferromagnetic/ferroelectric films, microstructure peculiarities.
1. Introduction
The discovery of colossal magnetoresistance (CMR)
in doped manganite perovskites [1] with the general
formula R Ax x1� MnO3, where R is a rare-earth cation
and A is an alkali or alkaline earth cation [2,3], has
stimulated numerous investigations not only because
of their interesting fundamental science but because of
possibilities for device applications. For a great num-
ber of these potential industrial applications, these
materials have to be prepared in the form of thin films
or multilayered hybrid systems. However, the manga-
nite thin films frequently show different magne-
totransport properties in comparison to bulk materi-
als. The observed discrepancy is mainly explained by
the accumulation of lattice strain due to the epitaxial
growth of the film, which plays an important role in
formation of the spin-ordered state and the value of
CMR effect [4–13]. It has been declared, for example,
that a lattice compression will reduce the elec-
tron–phonon interaction and increase the electronic
hopping amplitude by decreasing the Mn–O bond
© V.G. Prokhorov, V.A. Komashko, G.G. Kaminsky, K.K. Yu, S.J. Jun, S.Y. Park, J.S. Park, Y.P. Lee, and V.L. Svetchnikov, 2006
length while increasing the Mn–O–Mn bond angle,
all leading to increase of the Curie temperature TC. In
contrast, the Jahn–Teller distortion will lead to a lo-
calization of electrons and reduce TC [4]. This phe-
nomenon is described, as a rule, on the basis of the
Millis model [14], developed for materials with weak
lattice strains and a cubic symmetry. On the other
hand, the recently observed suppression of the contri-
bution from the Jahn–Teller distortion to the ferro-
magnetic ordering with increasing lattice mismatch
between substrate and film [7,12,13,15,16] demon-
strates a physical limitation of the weak-strain ap-
proach [14] in describing the magnetic properties of
manganite films. Moreover, it has been shown that the
microstructure features [9,16–18] and the oxygen con-
tent [6,19–25] can lead to considerable change in the
magnetotransport properties of the films, as well.
In spite of the fact that the influence of kind of sin-
gle-crystalline substrates on the magnetic and the
electronic properties of manganite films has been quite
well investigated, the development of hybrid devices
such as ferromagnetic/ferroelectric ones, which are
very promising for modern applications [26], needs
detailed information on the microstructure of inter-
faces and the mutual influence between heterogeneous
layers.
In this paper, we report the experimental results
for the LCMO/BTO and the LSMO/BTO hybrid
ferromagnetic/ferroelectric films. For comparison,
we present the same data for the films deposited on
the bare LAO and SrTiO3 (STO) substrates. The ob-
served difference in the growth mechanism of the
LCMO and the LSMO films and the influence of the
lattice strain and the microstructure peculiarities on
the magnetotransport properties are discussed in de-
tail.
2. Experimental techniques
The films were prepared by an on-axis rf-magnetron
sputtering using a so-called «soft» (or powder) target
[27]. The substrate was a LAO (001) single crystal
with an out-of-plane lattice parameter of c � 0.379 nm
for the pseudocubic symmetry. The total pressure
in chamber was 4·10 �2 Torr with a gas mixture of
Ar and O2 (2:1). The substrate temperature during
deposition was 750 �C. The LCMO/BTO and the
LSMO/BTO bilayers were prepared with thicknesses
for LCMO, LSMO, and BTO of d � 160, 160, and 100
nm, respectively. For comparison, the bare BTO,
LCMO, and LSMO films with the same thicknesses
were deposited on the LAO substrate at the similar
conditions. The LSMO films were prepared with
d � 70 nm onto the STO substrate as well. The �–2�
x-ray diffraction (XRD) patterns were obtained using
a Rigaku diffractometer with Cu K� radiation. The
high-resolution electron-microscopy (HREM) studies
were carried out using a Philips CM300UT-FEG mi-
croscope with a field emission gun operated at 300 kV.
The point resolution of the microscope was of the or-
der of 0.12 nm. The cross-sectional specimens were
prepared by the standard techniques using mechanical
polishing followed by ion-beam milling at a grazing
incidence. All microstructure studies were carried out
at room temperature. The resistance measurements
were performed by using four-probe method in a tem-
perature range of 4.2–300 K and a magnetic field up to
5 T. The in-plane field-cooled (FC) and zero-field-
cooled (ZFC) magnetization curves under an applied
magnetic field of 100 Oe and the magnetization hys-
teresis loops at 10 K were taken with a Quantum De-
sign SQUID magnetometer.
3. Microstructures of the films
Figure 1,a shows the �–2� XRD scan for the BTO
film deposited on the LAO substrate. The high inten-
sity of the (00l) peaks indicates that the deposition re-
sults in highly c-oriented film. The obtained out-
of-plane lattice parameter (c � 0.407 nm) is not very
different from the bulk value at room temperature,
c � 0.4033 nm [28]. Figures 1,b and 1,c display, in de-
tail, the (004) Bragg peaks for the LCMO/BTO and
the LCMO/LAO, and the LSMO/BTO and
the LSMO/LAO films, respectively. The analysis of
XRD data reveals that the out-of-plane lattice param-
Magnetic and transport properties driven by lattice strain
Fizika Nizkikh Temperatur, 2007, v. 33, No. 1 79
20 30 40 50 60 70
10
0
10
1
10
2
10
3
10
4
a
(0
0
3
)
L
A
O
B
T
O(0
0
2
)
LA
O
B
T
O
(0
0
1
)
LA
O
B
T
O
2 ,� degree
9 95 51 10 00 01 10 05 5
2
4
6
8 b
2
1 LC
M
O
LC
M
O
B
T
O
In
te
n
si
ty
, 1
0
cp
s
3
In
te
n
si
ty
, c
p
s
10
20
30
LS
M
O
LS
M
O
21
B
T
O
c
Fig. 1. �–2� XRD pattern for the BTO/LAO film (a).
The (004) Bragg peaks for the LCMO and the LSMO
films, respectively, deposited on BTO (1) and LAO (2)
(b) and (c).
eter for LCMO/LAO corresponds to c � 0.39 nm,
while c � 0.3857 nm for LCMO/BTO. Similar
to that c � 0.3891 nm for LSMO/LAO while
c � 0.3872 nm for LSMO/BTO.
Figure 2 presents the low-magnification cross-sec-
tional HREM image of the BTO film (a) and the
high-magnification one for a region including the
BTO/LAO interface (b). The inset in Fig. 2,b dis-
plays the fast Fourier transform (FFT) of the
high-magnification HREM image. The FFT of the
HREM image across the BTO/LAO interface reveals
elongated and slightly split spots in both the c (nor-
mal to the interface) and a (along the interface) direc-
tions (indicated by the black arrows in Fig. 2,b). This
is evidence for the semicoherent (or weakly coherent)
lattice coupling between LAO and BTO. Due to the
large mismatch between substrate and film, misfit dis-
locations are formed in BTO near the interface, as is
displayed in Fig. 2,c. The corresponding Buerger’s cir-
cuit is indicated by the white line. The measurement
of various interspot spacings on the high-magnifica-
tion HREM image allows us to obtain average values
of the lattice parameters. Analysis reveals that the
BTO film has a tetragonal crystal lattice with c �
� 0.407 nm and c/a � 1.02. The obtained lattice pa-
rameters are almost coincident with those for the bulk
[28] and for the BTO films deposited on SrTiO3
(a � 0.3905 nm) [29].
Figure 3 presents (a) the low- and (b) high-mag-
nification cross-sectional HREM images of the
LCMO/BTO bilayered film. It is seen that FFT (c)
of the LCMO/BTO HREM image across the inter-
face produces a rectangular pattern of the spots,
which are elongated only along the out-of-plane direc-
tion without a visible splitting or an elongation in the
in-plane direction. This indicates that almost coherent
interface is formed between BTO and LCMO. Analy-
sis of the interspot spacings and the angles between
spot rows and columns reveals that the LCMO layer
has a tetragonal crystal structure with c � 0.386 nm,
which is in good agreement with the XRD data, and
has a reversed (with respect to BTO) tetragonal ratio,
c/a � 0.98. The estimated in-plane lattice parameter
for LCMO, a � 0.394 nm, turns out to be very close to
that for BTO, a � 0.399 nm.
For comparison a similar microstructural analysis
has been carried out for the LCMO film deposited di-
rectly on LAO, which is represented by Fig. 4. FFT in
this case produces a rectangular pattern similar to that
for the LCMO/BTO interface, with a well-defined
spot splitting in the out-of-plane direction and slight-
ly elongated spots along the in-plane direction, mani-
80 Fizika Nizkikh Temperatur, 2007, v. 33, No. 1
V.G. Prokhorov et al.
c
*
b
LAO
5 nm
BTO
c
a
50 nm
Fig. 2. Low-magnification cross-sectional HREM image
for BTO/LAO film (a). High-magnification cross-sectio-
nal HREM image for the BTO/LAO interface. Dashed
line indicates the interface. Inset is corresponding FFT
(b). The misfit dislocation formed in BTO film near inter-
face. An associated Burgers circuit is indicated by the
white line (c).
100 nm
����
���
���
a
b
LCMO
BTO 4 nm
c
c
*
Fig. 3. Low-magnification cross-sectional HREM image for
LCMO/BTO film (a). High-magnification cross-sectional
HREM image of the LCMO/BTO interface. Dashed line
indicates the interface (b). FFT of the HREM image in
Fig. 3,b (c).
festing a nearly coherent interface between the film
and the substrate. The LCMO/LAO film reveals a
tetragonal crystal lattice with c � 0.39 nm, which is
perfectly coincident with the corresponding XRD
data, and c/a � 1.015.
The same cross-sectional HREM images for
LSMO/BTO and LSMO/LAO are represented in
Figs. 5 and 6, respectively. For both films the FFTs
result in the slightly elongated spots along both the
in-plane and the out-of-plane directions. The analysis
of the high-magnification HREM images reveals that
the tetragonal distortion of the LSMO layers is signif-
icantly smaller then that for LCMO ones: c/a � 0.996
for LSMO/BTO and c/a � 1.008 for LSMO/LAO.
Insets in Figs. 5,b and 6,b display moire patterns (in-
verse Fourier transforms [30]) of the high-magnifica-
tion HREM images across interface for LSMO/BTO
and LSMO/LAO, respectively. It is seen that in both
cases the edge dislocations are formed in the LSMO
film (noted by white arrows). Moreover, these dislo-
cations can be of opposite sign. Therefore, one can
conclude that a semicoherent interface between the
substrate and film is formed in the deposition of
LSMO.
The lattice parameters and the estimated values of
the in-plane (�100 � �( )a a /abulk film bulk) and out-
of-plane (�001 � �( )c c /cbulk film bulk) lattice strains
for investigated samples are summarized in Table 1.
Table 1 also contains the data for the LSMO/STO
Magnetic and transport properties driven by lattice strain
Fizika Nizkikh Temperatur, 2007, v. 33, No. 1 81
100 nm
a
b
5 nm
c
c
*
Fig. 4. Low-magnification cross-sectional HREM image for
LCMO/LAO film (a). High-magnification cross-sectional
HREM image of the LCMO/LAO interface. Dashed line
indicates the interface (b). FFT of the HREM image in
Fig. 4,b (c).
a
����
���
���
100 nm
bLSMO
BTO
4 nm
c
c
*
Fig. 5. Low-magnification cross-sectional HREM image for
LSMO/BTO film (a). High-magnification cross-sectional
HREM image of the LSMO/BTO interface. Dashed line
indicates the interface. Inset shows moire pattern across
the interface with misfit dislocations (indicated by white
arrows) (b). FFT of the HREM image in Fig. 5,b (c).
a
100 nm
b
5 nm
c
Fig. 6. Low-magnification cross-sectional HREM image for
LSMO/LAO film (a). High-magnification cross-sectional
HREM image of the LSMO/LAO interface. Dashed line
indicates the interface. Inset shows moire pattern across
the interface with misfit dislocations (indicated by white
arrows) (b). FFT of the HREM image in Fig. 6,b (c).
film with d � 160 nm and for the LSMO/BTO and
the LSMO/LAO thin (d � 70 nm) films, for compari-
son. The following lattice parameters for bulk were
employed in this evaluation: abulk � 0.3864 nm and
cbulk � 0.3875 nm for La07. Ca03. MnO3 [31] and
aR
bulk � 0.548 nm and �R
bulk � 60.3� for
La07. Sr03. MnO3 [32].
Therefore, two kinds of the films with different
sign of the lattice strain have been prepared:
LCMO/BTO and LSMO/BTO have biaxial tensile
in-plane and compressive out-of-plane strains, while
LCMO/LAO and LSMO/LAO are subjected re-
versely, to compressive in-plane and tensile out-of-
plane strains. On the other hand, it is seen that the
LCMO films are more susceptible to the crystal struc-
ture of the substrate and accumulate more lattice
strains during deposition in comparison to the LSMO
ones. The observed difference in the lattice-strained
state for these films can be governed by the peculiari-
ties of the growth mechanism. Recently it was shown
that the LSMO films tend toward stress relaxation
during growth by the formation of misfit dislocations,
while the LCMO films form a column-like strained
microstructure [33–35]. This agrees well with our re-
sults, which testify that the LCMO films demonstrate
a dislocation-free epitaxial growth mode with the for-
mation of a strong lattice-strained state. These biaxial
strains accommodate, during the film growth, in form-
ing a coherent columnar microstructure directed along
the interface normal which can be treated as prismatic
antiphase boundaries. However, in the LSMO films a
strain accommodation is realized owing to the forma-
tion of misfit dislocations.
4. Magnetic and transport properties
Figure 7 shows the in-plane FC (solid symbols) and
ZFC (open symbols) temperature-dependent magneti-
zation curves, M(T), for the LCMO/BTO (1) and
the LCMO/LAO (2) systems. The applied magnetic
field was H = 100 Oe. The LCMO/BTO bilayer
manifests the onset of ferromagnetic ordering at
TC � 250 K, while LCMO/LAO has a Curie point at
a lower temperature TC � 230 K, which is typical for
82 Fizika Nizkikh Temperatur, 2007, v. 33, No. 1
V.G. Prokhorov et al.
Table 1. Results of the XRD and the HREM analysis for the investigated films.
Samples Out-of-plane lattice Tetragonal ratio, In-plane Out-of-plane Bulk strain, Jahn–Teller
parameter, c (nm), c/a, strain, strain, strain,
XRD data HREM data �100 (%) �001 (%) �B (%)* �JT (%)**
BTO/LAO 0.407 1.02 0.12 –0.92 –0.68 –0.84
LCMO/BTO 0.3857 0.99 –0.93 0.46 –1.4 1.14
LCMO/LAO 0.39 1.015 0.57 –0.64 0.49 –1.0
LSMO/BTO 0.3872 0.996 –0.36 0.53 –0.2 0.73
LSMO/LAO 0.3891 1.008 0.6 –0.19 1.01 –0.65
LSMO/STO 0.3869 0.993 –0.1 0.6 0.41 0.57
LSMO/BTO*** 0.3864 0.98 –1.29 0.73 –1.86 1.66
LSMO/LAO*** 0.3903 1.01 0.72 –0.27 1.17 –0.81
Notes: * — � � ��� �B 100 001� ); ** — � � �JT � �2 3 001 100/ ( ); *** — thickness of the LSMO layer is d � 70 nm.
0 100 200 300
1
2
3
4
5
100 Oe
ZFC
FC
2 1
T, K
–2 0 2
–1
0
1 10 K
H, kOe
M
, 1
0
e
m
u
–
4
M
,1
0
e
m
u
–
3
Fig. 7. Temperature dependence of the FC (solid symbols)
and ZFC (open symbols) magnetizations for LCMO/BTO
(1) and LCMO/LAO (2). Inset displays the in-plane mag-
netic hysteresis loops for LCMO/BTO (solid symbols)
and LCMO/LAO (open symbols) at 10 K. Lines are a
guide to the eye.
the lattice-strained as-deposited film [9,10,12,36].
The inset in Fig. 7 displays the in-plane magnetic
hysteresis loops, measured at T � 10 K, for the
LCMO/BTO (solid symbols) and the LCMO/LAO
(open symbols) films. The M(H) for LCMO/BTO is
narrower (the coercive field is Hc � 100 Oe) and satu-
rates twice as fast (the saturation field is Hs �
� 3000 Oe), as compared to LCMO/LAO (Hc �
� 300 Oe and Hs � 6000 Oe) which can be explained
by a strain-driven magnetic anisotropy in these films
[5,37].
Figure 8 displays the similar magnetization depend-
encies for LSMO/LAO (1), LSMO/BTO (2),
and LSMO/STO (3) films. The maximal temperature
of the ferromagnetic ordering is observed for
LSMO/STO, TC � 315 K, while the lowest one be-
longs to LSMO/LAO, TC � 296 K. The LSMO/BTO
film has TC � 310 K. The inset in Fig. 8 shows that
the coercive field is the same for all the LSMO films,
Hc � 100 Oe, while the saturation field is consider-
ably dependent on the substrate: Hs � 4000, 1200,
and 800 Oe for LSMO/LAO, LSMO/STO, and
LSMO/BTO, respectively.
Figure 9 is the temperature-dependent resistance,
R(T), for the LCMO/BTO (1) and the LCMO/LAO
(2) films without (solid symbols) and with (open
symbols) an applied magnetic field of 5 T. The mag-
netic field was directed parallel to the film surface and
at right angles to the transport current. It is seen that
the LCMO/BTO bilayer undergoes the metal–in-
sulator (MI) transition at TP � 230 K, while the
LCMO/LAO film manifests TP � 195 K. In both
cases the temperature of MI transition is lower than
the corresponding Curie point and understood by a
percolating nature of the MI transition [38]. The inset
in Fig. 9 presents the temperature dependence of nega-
tive magnetoresistance (MR) for LCMO/BTO (1)
and LCMO/LAO (2). The MR value is defined
by 100% � [R(0) – R(H)]/R(H), where R(0) and
R H( ) are the resistances without and with a magnetic
field of 5 T.
Figure 10 displays the similar R(T) dependencies
without (solid symbols) and with (open symbols) an
applied magnetic field of 5 T for the thin (d � 70 nm)
LSMO/LAO (1) and LSMO/BTO (2), and thick
(d � 160 nm) LSMO/BTO (3) and LSMO/LAO (4)
films. Inset (a) shows the temperature dependence of
the MR value for these films. Because the LSMO
manganite does not undergo a real MI transition near
the Curie point and manifests only a change in the
slope of the R(T) dependence, the MI temperature was
obtained from analysis of the first derivative of R(T)
versus T curves, which are presented in the inset (b).
It is seen that for thick LSMO/BTO and
LSMO/LAO TP � 275 and 250 K, while for thin
ones TP � 260 and 220 K, respectively (denoted by ar-
Magnetic and transport properties driven by lattice strain
Fizika Nizkikh Temperatur, 2007, v. 33, No. 1 83
0 100 200 300
5
10
100 Oe3
2
1
T , K
2 1 0 –1 –2
1
0
10 K
2, 3
1
H, kOe
M
, 1
0
e
m
u
–
4
M
,1
0
e
m
u
–
3
–1
Fig. 8. Temperature dependence of the FC (solid symbols)
and ZFC (open symbols) magnetizations for LSMO/LAO
(1), LSMO/BTO (2), and LSMO/STO (3). Inset dis-
plays the in-plane magnetic hysteresis loops at 10 K. Lines
are a guide to the eye.
50 1 0 150 200 250
2
4
6
8
12
T, K
100 200
2
4
6
12
T, K
M
R
, 1
0
%2
R
, 1
0
3
�
0
Fig. 9. Temperature dependence of the resistance for
LCMO/BTO (1) and LCMO/LAO (2) without (solid
symbols) and with (open symbols) an applied magnetic
field of 5 T. Inset includes the temperature-dependent MR
ratios. Lines are a guide to the eye.
rows). Some of the magnetotransport characteristics
for the investigated films are summarized in Table 2.
5. Discussion
Let us analyse the obtained results on the basis of
Millis model [14]. For weak lattice strain and a cubic
symmetry TC can be expressed by:
T TC C B JT( ) ( )� � �� �� � � ��
�
�
0 1
1
2
2� ,
where � �� ( )( )1/T dT /dC C B , and � � �( )1/TC
� ( )d T /dC JT
2 2� , (dT /dC JT� � 0 by cubic symmetry).
The magnitudes of � and � represent the relative
weights for the symmetry-conserving bulk and the
symmetry-breaking Jahn–Teller strains, respectively.
Here � � �B � �( )2 100 001 is a bulk strain and
� � �JT /� �2 3 001 100( ) is a Jahn–Teller strain. Ba-
sed on the dynamical «mean field» approximation
[39] and considering the electron–phonon coupling
due to the Jahn–Teller splitting [40], one can calcu-
late numerically the compressive (�) and uniaxial (��
strain dependence as function of the elecron–phonon
interaction. According to the model [14], � � 10 for
a reasonable the electron–phonon coupling (0.5 � ��
� 1) in these compounds, where � is the elec-
tron–phonon interaction constant, and � � 5000.
Taking into account that the Curie temperature for
the strain-free bulk La07. Ca03. MnO3 compound is
TC(� � 0) � 265 K [41], and using the values ob-
tained for �B , �JT , and TC, we estimated � as 3000
and 1500 for LCMO/BTO and LCMO/LAO, re-
spectively, which agree in principle with the model
prediction. On the other hand, the same analysis car-
ried out for the LSMO films showed a larger disagree-
ment with theoretical model. The estimated values of
� change to 7000, 5000, and 800 for LSMO/BTO,
LSMO/LAO, and LSMO/STO, respectively. The
Curie point of 375 K was used for the strain-free bulk
La07. Sr03. MnO3 compound [32]. A similar strong dis-
crepancy between the model and the experiment was
recently observed for the LCMO films deposited on
STO and NdGaO3 [15,16]. The main explanation for
this disagreement is based on the existence of a dead
layer or parasitic phase located at the film/substrate
interface, which leads to an additional influence on
the Curie temperature together with lattice strain
[15,16,42]. However, the cross-sectional HREM im-
ages did not manifest the appearance of any extensive
defects close to the interface in the investigated films,
and the temperature-dependent magnetization curves
attest to the existence a single-phase magnetic state
only. We believe that the following main reasons lead
to the observed disagreement. The first of them is
84 Fizika Nizkikh Temperatur, 2007, v. 33, No. 1
V.G. Prokhorov et al.
50 100 150 200 250 300
10
1
10
2
4
3
2
1
T , K
100 200
50
100a
4
3
2
1
T, K
200 250
2
4
6 b
4
3
2
1
T, K
M
R
,%
d
R
/d
T
,
a
rb
. u
n
its
R
, �
Fig. 10. Temperature dependence of the resistance for
LSMO/LAO (1) and LSMO/BTO (2) with d = 70 nm,
and LSMO/BTO (3) and LSMO/LAO (4) with d =
= 160 nm without (solid symbols) and with (open sym-
bols) an applied magnetic field of 5 T. Inset (a) includes
the temperature-dependent MR ratios. Inset (b) displays
the temperature-dependent first derivative dR dT/ . (MI
transition temperatures indicated by arrows).
Table 2. Magnetotransport characteristics for the investigated films
Samples Curie point, Coercive field,
Saturation
field,
Remanence, Magnetoresistance*, MI transition,
TC, K Hc, Oe Hs, Oe M /Msr , % MR, % TP, K
LCMO/BTO 250 100 3000 61 550 (17) 230
LCMO/LAO 230 300 6000 59 760 (9) 195
LSMO/BTO 310 100 800 73 80 (65) 275
LSMO/LAO 296 100 4000 31 50 (43) 250
LSMO/STO 315 100 1200 70 40 (38) 280
Notes: * — in brackets are MR values at 300 K.
connected with the relatively random selection of the
bulk lattice parameters for an estimation of the in-
plane and the out-of-plane strains, owing to the
strong variations between the experimental data
which can be found in the literature [22,31–35,41,
43–45]. Secondly, even annealed strain-free films
have different unit cell volume compared to the bulk
materials [42,44]. Therefore, we are sure that the cor-
rect testing of the Millis model [14] for the CMR
films must be carried out using the lattice parameters
of the annealed films as the «bulk» rather than those
of the real bulk materials.
On the other hand, the elastic stress intensity in
these films can be identified with the tetragonal dis-
tortion of the crystal lattice. Table 1 shows that the
tetragonal ratios are larger for the LCMO than for the
LSMO films. This can be explained by the different
mechanism of growth of these films. The HREM data
reveal that LCMO demonstrates the epitaxial mode,
with the formation of an almost coherent interface be-
tween the substrate and the film, while the growth of
LSMO is accompanied by dislocation formation that
results in a semicoherent interface.
Let us consider in detail influence of the lattice
strained state and the microstructure features on
magnetotransport properties of the investigated films.
Figure 7 shows that LCMO/BTO with a biaxial
tensile in-plane lattice strain undergoes the magnetic
transition at higher temperature than that observed
in LCMO/LAO, with biaxial compressive strains.
It is well known that the electronic transfer integral
in CMR could be determined mainly by Mn–O
bond length and Mn–O–Mn angle [46]. The final re-
sult for TC can be approximately written as TC �
� cos .�/dMn–O
35 , where � is the tilt angle in the plane
of the bond, and dMn–O is the Mn–O bond length
[47,48]. It is believable that the tetragonal elastic de-
formation of a crystal lattice, provided by compressive
and tensile strains, results in a simultaneous change of
the Mn–O bond length and the Mn–O–Mn angle, ow-
ing to the distorted vertex-sharing of MnO6 octahedra
[49]. Taking into account that the biaxial tensile
in-plane lattice strain increases the Mn–O bond
length, it would be reasonable to expect a significant
lowering of the Curie point for the LCMO/BTO
film, in disagreement with the experimental results.
Therefore, one can conclude that the variation of the
Mn–O–Mn bond angle, controlled by a lattice strain,
plays more important role in the formation of the spin
ordering in the CMR film than the attendant modifi-
cation of the Mn–O bond length.
Table 2 shows that the LCMO/BTO film has a
lower saturation field and larger remanent magnetiza-
tion as compared with the LCMO/LAO film. This ef-
fect is provided by the magnetic anisotropy of strained
epitaxial films, which is strongly correlated with the
nature of the substrate-induced lattice strain states. It
was shown that the easy axis magnetization always
takes up a position along the direction of the tensile
strain [5,8]. Consequently, in the LCMO/BTO film
an in-plane biaxial magnetic anisotropy is observed,
while the easy axis magnetization is perpendicular to
the LCMO/LAO film plane. The observed increase of
the coercive field for LCMO/LAO can be connected
with the column-like texture of the film [33–35],
which can play the role of additional pinning centers
for magnetic domain walls during a magnetization re-
versal.
The LSMO films also demonstrate the influence of
the substrate-induced lattice strain on the magnetic
properties, but this effect is manifested more slightly
in comparison with the LCMO ones. Similar to
LCMO, the LSMO/BTO and LSMO/STO films
with a biaxial tensile in-plane lattice strain demon-
strate higher Curie temperatures than that observed in
the LSMO/LAO film. This implies that in the LSMO
films the ferromagnetic ordering is governed by the
tilt bond angle rather than the Mn–O bond length, as
well.
The relatively small value of the saturation field
and the high remanence testify that the LSMO films
deposited on BTO and STO have in-plane easy-axis
magnetization, in contrast to LSMO/LAO, which is
also coincident with data for the LCMO films. On the
other hand, the coercive field remains the same for all
films and does not depend on the substrate material.
Therefore, the prepared LSMO films do not have
large-size microstructure faults (for example, such as
column-like texture in LCMO/LAO [33–35]) that
could pin the magnetic domains during magnetization
reversal.
Figures 7 and 8 show that the difference between
ZFC and FC magnetization curves at low temperature
essentially depend on the substrate material. This phe-
nomenon is usually treated as an existence of the in-
trinsic inhomogeneous magnetic (or «cluster» glass)
state governed by the tendency of CMR toward elec-
tronic phase separation [38]. Let us to express the
degree of magnetic inhomogeneity in the films by
�MZFC
FC � 100% � [ ( ) ( )] ( )M T M T /M TFC ZFC FC� ,
where M TFC( ) and M TZFC( ) are the FC and ZFC
magnetizations at a certain temperature. The �MZFC
FC
values turn out to be significantly different for the inves-
tigated films: 93, 74, 37, 20, and 0% for LCMO/LAO,
LCMO/BTO, LSMO/LAO, LSMO/BTO, and
LCMO/STO, respectively, at T � 0. The higher de-
gree of magnetic inhomogeneity is observed in the
LCMO films with larger tetragonal distortion of crys-
Magnetic and transport properties driven by lattice strain
Fizika Nizkikh Temperatur, 2007, v. 33, No. 1 85
tal lattice (see Table 1) and a columnar microstruc-
ture [33–35,50], which is formed through the biaxial
in-plane strain accommodation. In contrast to that the
LSMO films demonstrate smaller tetragonal distor-
tion of crystal lattice due to introduction of the misfit
dislocations during its growth that is resulted in
a more regular microstructure and a small degree of
magnetic inhomogeneity. Therefore, this kind of mag-
netic inhomogeneity, which is connected with the ob-
served difference in FC and ZFC M T( ) dependences,
has a metallurgical rather than an electronic nature,
and is controlled by the crystal lattice distortion and
the microstructure defects.
The temperature dependencies of resistance repre-
sented by Figs. 9 and 10 manifest mainly a typical for
the CMR films behavior. For example, the MI transi-
tion temperature, which is treated as a peak on the
R T( ) curve (for the LSMO films it is a peak on the
first derivative dR T /dT( ) curve), is strongly corre-
lated with the Curie point and in our case can be ex-
pressed by a simple empirical relation: TP � 0.92TC �
11.6 K. On the other hand, the usual increase of the
MR value with decreasing TP is observed only for the
LCMO films. Insets (a) and (b) in Fig. 10 show that
the LSMO/BTO films demonstrate larger MR values
in comparison to the LSMO/LAO ones, though their
MI transition temperatures are higher, as well. Thus,
MR = 80 and 110%, and TP � 275 and 260 K for
LSMO/BTO with d � 160 and 70 nm, respectively,
while MR = 50 and 91%, and TP � 250 and 220 K for
LSMO/LAO with d � 160 and 70 nm, respectively.
Therefore, the deposition of the LSMO film on the
BTO layer leads to an increase of the magneto-
resistance effect. Moreover, the LSMO/BTO
bilayered film demonstrates the maximal MR value at
room temperature: � 65%.
6. Conclusions
We have performed magnetotransport measure-
ments on LCMO/BTO and LSMO/BTO bilayered
films deposited by rf-magnetron sputtering, using
«soft» (or powder) targets. For comparison,
LCMO/LAO, LSMO/LAO, and LSMO/STO films
have been prepared as well. The HREM analysis re-
veals: (i) first, the BTO layer has a tetragonal crystal
lattice, c-oriented along the normal to the film plane;
(ii) second, LCMO/BTO and LSMO/BTO have bi-
axial tensile in-plane and compressive out-of-plane
strains, while LCMO/LAO and LSMO/LAO are
subjected, reversely, to compressive in-plane and ten-
sile out-of-plane strains; (iii) third, LCMO forms a
coherent interface between substrate and film, while
LSMO has a semicoherent one owing to accumulation
of the misfit dislocations during deposition.
We have shown that films with a biaxial tensile
in-plane lattice strain undergo the magnetic transition
at a higher temperature than those with a biaxial com-
pressive strain. This argues that the variation of the
Mn–O–Mn bond angle, controlled by the lattice
strain, plays a more important role in the formation of
the spin ordering in the CMR film than the attendant
modification of the Mn–O bond length.
The LCMO/BTO, LSMO/BTO, and LSMO/STO
films manifest an in-plane magnetic anisotropy, while
the easy-axis magnetization is out-of-plane for the
LCMO/LAO and the LSMO/LAO films.
It was shown that the magnetic inhomogeneity,
connected with the observed difference in FC and
ZFC M(T) dependences, has a metallurgical rather
than an electronic nature, and is controlled by the
crystal lattice distortion and the microstructure de-
fects.
The observed enhancement of the magnetoresis-
tance effect in the LSMO/BTO bilayered film at
room temperature make its greatly beneficial in the
development of new hybrid ferromagnetic/ferroelec-
tric devices.
This work was supported by the KOSEF through
the Quantum Photonic Science Research Center.
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