Magnetic and transport properties controlled by structural disorder in La₀.₇Ca₀.₃MnO₃ films
The magnetic properties of an amorphous, a partially-disordered, and a lattice-strained crystalline La₀.₇Ca₀.₃MnO₃ film are investigated. It is shown that the amorphous film exhibits Curie- Weiss-type paramagnetism with the effective magnetic moment of 4.2 µB/Mn ion and a small ferromagnetic c...
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Prokhorov, V.G. Komashko, V.A. Kaminsky, G.G. Svetchnikov, V.L. Lee, Y.P. Park, S.Y. 2017-06-10T07:30:05Z 2017-06-10T07:30:05Z 2004 Magnetic and transport properties controlled by structural disorder in La₀.₇Ca₀.₃MnO₃ films / V.G. Prokhorov, V.A. Komashko, G.G. Kaminsky, V.L. Svetchnikov, Y.P. Lee, S.Y. Park // Физика низких температур. — 2004. — Т. 30, № 9. — С. 938–944. — Бібліогр.: 21 назв. — англ. 0132-6414 PACS: 71.30.+h, 75.47.Gk, 75.47.Lx https://nasplib.isofts.kiev.ua/handle/123456789/119849 The magnetic properties of an amorphous, a partially-disordered, and a lattice-strained crystalline La₀.₇Ca₀.₃MnO₃ film are investigated. It is shown that the amorphous film exhibits Curie- Weiss-type paramagnetism with the effective magnetic moment of 4.2 µB/Mn ion and a small ferromagnetic contribution governed by the formation of a quasi-two-dimensional crystalline interfacial inclusions. The crystalline film with nanocrystalline randomly-oriented inclusions demonstrates a superposition of ferromagnetic (in the crystalline matrix) and superparamagnetic (in the inclusions) nature. The fitted average size of the superparamagnetic particles in the case of a Langevin function is coincident with that of the nanocrystalline clusters reveated in high-resolution electron-microscopy images. An increase in the applied magnetic field leads to a reduction in the average magnetic moment of superparamagnetic particles, which is due to an enhancement of the ferromagnetic coupling between the individual randomly-oriented crystallites. The completely crystalline film undergoes only a ferromagnetic transition with a saturation magnetization at 5 K of 2.73 µB /Mn ion. This work was supported by the KOSEF through the Quantum Photonic Science Research Center. en Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України Физика низких температур Низкотемпеpатуpный магнетизм Magnetic and transport properties controlled by structural disorder in La₀.₇Ca₀.₃MnO₃ films Article published earlier |
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Magnetic and transport properties controlled by structural disorder in La₀.₇Ca₀.₃MnO₃ films |
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Magnetic and transport properties controlled by structural disorder in La₀.₇Ca₀.₃MnO₃ films Prokhorov, V.G. Komashko, V.A. Kaminsky, G.G. Svetchnikov, V.L. Lee, Y.P. Park, S.Y. Низкотемпеpатуpный магнетизм |
| title_short |
Magnetic and transport properties controlled by structural disorder in La₀.₇Ca₀.₃MnO₃ films |
| title_full |
Magnetic and transport properties controlled by structural disorder in La₀.₇Ca₀.₃MnO₃ films |
| title_fullStr |
Magnetic and transport properties controlled by structural disorder in La₀.₇Ca₀.₃MnO₃ films |
| title_full_unstemmed |
Magnetic and transport properties controlled by structural disorder in La₀.₇Ca₀.₃MnO₃ films |
| title_sort |
magnetic and transport properties controlled by structural disorder in la₀.₇ca₀.₃mno₃ films |
| author |
Prokhorov, V.G. Komashko, V.A. Kaminsky, G.G. Svetchnikov, V.L. Lee, Y.P. Park, S.Y. |
| author_facet |
Prokhorov, V.G. Komashko, V.A. Kaminsky, G.G. Svetchnikov, V.L. Lee, Y.P. Park, S.Y. |
| topic |
Низкотемпеpатуpный магнетизм |
| topic_facet |
Низкотемпеpатуpный магнетизм |
| publishDate |
2004 |
| language |
English |
| container_title |
Физика низких температур |
| publisher |
Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України |
| format |
Article |
| description |
The magnetic properties of an amorphous, a partially-disordered, and a lattice-strained crystalline
La₀.₇Ca₀.₃MnO₃ film are investigated. It is shown that the amorphous film exhibits Curie-
Weiss-type paramagnetism with the effective magnetic moment of 4.2 µB/Mn ion and a small
ferromagnetic contribution governed by the formation of a quasi-two-dimensional crystalline interfacial
inclusions. The crystalline film with nanocrystalline randomly-oriented inclusions demonstrates
a superposition of ferromagnetic (in the crystalline matrix) and superparamagnetic (in the
inclusions) nature. The fitted average size of the superparamagnetic particles in the case of a
Langevin function is coincident with that of the nanocrystalline clusters reveated in high-resolution
electron-microscopy images. An increase in the applied magnetic field leads to a reduction in
the average magnetic moment of superparamagnetic particles, which is due to an enhancement of
the ferromagnetic coupling between the individual randomly-oriented crystallites. The completely
crystalline film undergoes only a ferromagnetic transition with a saturation magnetization at 5 K
of 2.73 µB /Mn ion.
|
| issn |
0132-6414 |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/119849 |
| citation_txt |
Magnetic and transport properties controlled by structural disorder in La₀.₇Ca₀.₃MnO₃ films / V.G. Prokhorov, V.A. Komashko, G.G. Kaminsky, V.L. Svetchnikov, Y.P. Lee, S.Y. Park // Физика низких температур. — 2004. — Т. 30, № 9. — С. 938–944. — Бібліогр.: 21 назв. — англ. |
| work_keys_str_mv |
AT prokhorovvg magneticandtransportpropertiescontrolledbystructuraldisorderinla07ca03mno3films AT komashkova magneticandtransportpropertiescontrolledbystructuraldisorderinla07ca03mno3films AT kaminskygg magneticandtransportpropertiescontrolledbystructuraldisorderinla07ca03mno3films AT svetchnikovvl magneticandtransportpropertiescontrolledbystructuraldisorderinla07ca03mno3films AT leeyp magneticandtransportpropertiescontrolledbystructuraldisorderinla07ca03mno3films AT parksy magneticandtransportpropertiescontrolledbystructuraldisorderinla07ca03mno3films |
| first_indexed |
2025-11-26T13:12:54Z |
| last_indexed |
2025-11-26T13:12:54Z |
| _version_ |
1850622200900485120 |
| fulltext |
Fizika Nizkikh Temperatur, 2004, v. 30, No. 9, p. 938–944
Magnetic and transport properties controlled by structural
disorder in La0.7Ca0.3MnO3 films
V.G. Prokhorov, V.A. Komashko, and G.G. Kaminsky
Institute of Metal Physics, National Academy of Sciences of Ukraine, Kiev 03142, Ukraine
E-mail: pvg@imp.kiev.ua
V.L. Svetchnikov
NCHREM, Rotterdamseweg 137, 2628AL, Delft, The Netherlands
Y.P. Lee and S.Y. Park
Quantum Photonic Science Research Center and Department of Physics, Hanyang University
Seoul 133-791, Korea
Received December 19, 2003, revised April 1, 2004
The magnetic properties of an amorphous, a partially-disordered, and a lattice-strained crystal-
line La07. Ca03. MnO3 film are investigated. It is shown that the amorphous film exhibits Cu-
rie-Weiss-type paramagnetism with the effective magnetic moment of 4.2 �B/Mn ion and a small
ferromagnetic contribution governed by the formation of a quasi-two-dimensional crystalline inter-
facial inclusions. The crystalline film with nanocrystalline randomly-oriented inclusions demon-
strates a superposition of ferromagnetic (in the crystalline matrix) and superparamagnetic (in the
inclusions) nature. The fitted average size of the superparamagnetic particles in the case of a
Langevin function is coincident with that of the nanocrystalline clusters reveated in high-resolu-
tion electron-microscopy images. An increase in the applied magnetic field leads to a reduction in
the average magnetic moment of superparamagnetic particles, which is due to an enhancement of
the ferromagnetic coupling between the individual randomly-oriented crystallites. The completely
crystalline film undergoes only a ferromagnetic transition with a saturation magnetization at 5 K
of 2.73 �B /Mn ion.
PACS: 71.30.+h, 75.47.Gk, 75.47.Lx
1. Introduction
The hole-doped perovskite manganites of the gen-
eral formula R1�xA xMnO3 (R — rare-earth cation,
A — alkali or alkaline-earth cation) have attracted
considerable attention not only because of their inter-
esting fundamental science, connected with the dis-
covery of colossal magnetoresistance (CMR), but also
their potential for device applications [1,2]. It was
found recently that the lattice strain (and stress), ac-
cumulated owing to the epitaxial growth of a film,
plays an important role in the formation of the spin-
and charge-ordered states in the CMR films [3–6].
The influence of the kind of single-crystalline sub-
strates on the magnetic and electronic properties of
manganite films has been quite will investigated [7,8].
It was shown that the presence of grain boundaries in
the polycrystalline manganites leads to a large MR ef-
fect over a wide temperature range below the Curie
temperature (TC), whereas the CMR of the single-crys-
talline materials is restricted to a narrower temperature
range just around TC [9–11]. On the other hand, the
influence of structural quench disorder on the magnetic
ordering is still poorly understood.
In this paper we report the peculiar results for
amorphous (LCM1), a strain-free crystalline (with
nanocrystalline mosaic-like inclusions) (LCM2), and
lattice-strained crystalline (LCM3) La07. Ca03. MnO3
film. It was shown that the state of Mn spins can be
controlled by a microstructure. We present an unusual
type of the randomly-oriented nanocrystalline mosaic
© V.G. Prokhorov, V.A. Komashko, G. G. Kaminsky, V.L. Svetchnikov, Y.P. Lee, and S.Y. Park, 2004
structure which manifests the magnetic-field-effected
superparamagnetic behavior and sheds new light on
the nature of magnetic ordering in the CMR materials.
2. Experimental techniques
All the films were prepared by rf-magnetron sput-
tering using a so-called «soft» (or powder) target
[12]. The total pressure in chamber was 5·10 �2 Torr
with a gas mixture of Ar and O2 (3 : 1). The substrate
was a LaAlO3 (001) single crystal (LAO) with a lat-
tice parameter a � 0.379 nm for the pseudocubic sym-
metry. The substrate temperature during deposition
was 20 (LCM1), 400 (LCM2), and 720 °C (LCM3).
All the films have a thickness of d � 30 nm. The � –2�
x-ray diffraction (XRD) patterns were obtained using
a Rigaku diffractometer with Cu K � radiation. The
lattice parameters evaluated directly from the XRD
data were plotted against cos sin2 � �. With an extra-
polated straight line to cos sin2 � � = 0, a more precise
determination of the lattice parameter was obtained.
Cross-section specimens were prepared by the standard
techniques using mechanical polishing followed by
ion-beam milling under grazing incidence. The high-re-
solution electron-microscopy (HREM) studies were car-
ried out using a Philips CM300UT-FEG microscope
with a field emission gun operated at 300 kV. The point
resolution of the microscope was of the order of 0.12 nm.
The resistance measurements were performed by using
the four-probe method in a temperature range of 4.2–300
K and in a magnetic field up to 5 T. The in-plane
field-cooled (FC) and zero-field-cooled (ZFC) magneti-
zation was taken with a Quantum Design SQUID mag-
netometer in a temperature range of 4.2–300 K.
3. Microstructure of the films
Figures 1,a and 1,b present the (001) and the (002)
Bragg reflections, respectively, for the LCM1 (1),
LCM2 (2), and LCM3 (3) films and for the LAO sub-
strate. The LCM1 film displays only a smooth plateau
instead of a real Bragg peak. Therefore, the film de-
posited at a low temperature is in an amorphous phase.
The LCM2 film shows weak Bragg peaks on a back-
ground of the same smooth plateau. The out-of-plane
lattice parameter for the LCM2 film, c � 0.3866 nm,
is very close to that for the bulk [13,14]. This suggests
that the incipient crystalline phase grows in equilib-
rium conditions without a significant influence of the
substrate and is formed through the amorphous state.
The LCM3 film, deposited at a high temperature, dis-
plays intense Bragg peaks with a larger out-of-plane
lattice parameter, c � 0.3927 nm, that is typical for
the thin CMR films and explained by the accumula-
tion of an in-plane biaxial compressive strain during
the deposition [7,8,12,15].
Figure 2,a is the high-magnification cross-sectional
HREM image for the amorphous LCM1 film. It was
obtained with an incident beam parallel to a cubic di-
rection of the substrate and to the film/substrate in-
terface. The inset in Fig. 2,a displays the fast Fourier
transform (FFT) of the HREM image across the inter-
face. It is seen that the FFT produces a bright uniform
halo instead of a rectangular pattern of circular spots.
Only the slightly luminescent spots corresponding to
the crystal lattice of the substrate are barely notice-
able. This coincides with the XRD data and confirms
an amorphous structure of the LCM1 film. On the
other hand, Fig. 2,b shows that a trace of a crystalline
phase is found on the substrate surface (denoted by
white arrows). The analysis of the HREM images re-
veals that this crystalline phase does not cover the
whole substrate surface and does not exceed one or
two unit cells in thickness. Figure 3,a demonstrates
the same HREM image for the LCM2 film. Even
though the FFT of LCM2 results in the formation of a
rectangular pattern of spots (see inset A in Fig. 3,a),
they are significantly smeared and include the bright
halo that testifies for presence of the amorphous (or
crystal-disordered) phase in the film. This sort of the
off-structural inclusion is represented in Fig. 3,b as
area A and the FFT of its as the inset. The wide ring in
FTT stands for the inclusions consists of the ran-
domly-oriented nano-scale crystallites. Therefore, in
this case we deal with the nanocrystalline mosaic
microstructure rather than with an amorphous one,
which was observed in LCM1. However, inset B in
Fig. 3,a shows that the matrix of LCM2 shows a per-
Magnetic and transport properties films controlled by structural disorder in La07. Ca03. MnO3
Fizika Nizkikh Temperatur, 2004, v. 30, No. 9 939
22 23 24 25
1
10
a
3
2
1
(001)
2�, degree
44 46 48 50
b
3
2
1
(002)
In
te
n
si
ty
,c
p
s
LC
M
3
LC
M
2
LC
M
1
LA
O
LC
M
3
LC
M
3 LC
M
2
LA
O
LC
M
1
10
5
104
10 3
10 2
Fig.1. (001) (a) and (002) (b) XRD peaks for the LCM1
(1), LCM2 (2), and LCM3 (3) films. LAO denotes the
substrate.
fect cubic crystalline lattice with the equal in-plane and
out-of-plane lattice parameters, a c� � 0.387 nm, and
right angle between the atom rows. It is matched with the
XRD data and proofs a strainless crystal lattice of the
LCM2 film. Figure 4 presents the HREM image for the
LCM3 film. In this case the FFT produces a well-defined
rectangular pattern of circular spots (see inset A) which
manifests formation of the perfect crystal lattice. However,
together with the perpendicular crystal axes, a tetragonal
distortion of the lattice (c a � 1.026) is also found in inset
B. The estimated in-plane lattice parameter for the LCM3
film, a � 0.3826 nm, is smaller than that for the bulk com-
pound, a � 0.3858 nm [14]. This difference leads to for-
mation of the aforementioned in-plane biaxial compressive
strain, �100 � �( )a a afilm bulk bulk , and an out-of-plane
uniaxial tensile strain, �001 � � �( )c c cfilm bulk bulk .
The performed calculations show that, in this case, � �
� – 0.83 and � � 1.79%. As far as the microstructural
measurements are summarized, it is noted that LCM1 is
mainly in an amorphous crystal structure, LCM2 contains
a complex of the strainless crystalline matrix with nano-
crystalline mosaic-type inclusions, and finally LCM3 rep-
resents a strained crystal lattice with a slight tetragonal
distortion.
4. Experimental results
Figure 5 shows both FC (solid) and ZFC (open)
temperature-dependent magnetization curves, M(T),
at a magnetic field H � 100 Oe for the LCM1 (a), the
LCM2 (b) and the LCM3 (c) films. The amorphous
LCM1 film demonstrates an M(T) behavior which is
typical for paramagnetic (PM) materials [16]. At the
same time, two peculiarities, a minor splitting be-
tween the ZFC and FC M(T) curves and a slight de-
crease in the magnetization near the expected Curie
point (denoted by arrow in Fig. 5,a), indicate the
presence of a ferromagnetic (FM) phase. It is claimed
that a small FM contribution is connected with the
mentioned ultrathin crystalline layer on the substrate
surface (see Fig. 2,b). The inset in Fig. 5,a displays
the M(H) dependence at room temperature, which
940 Fizika Nizkikh Temperatur, 2004, v. 30, No. 9
V.G. Prokhorov, V.A. Komashko, G. G. Kaminsky, V.L. Svetchnikov, Y.P. Lee, and S.Y. Park
LCM1
LAO3 nm
a
b
Fig. 2. Cross-sectional HREM image of the LCM1 film
near the interface. The inset is the corresponding FFT (a).
The same image with a crystalline monolayer on the sub-
strate surface, denoted by the white arrows (b).
a
LAO
3 nm
b
A
LCM2
B
c
a
A
2 nm
Fig. 3. Cross-sectional HREM image of the LCM2 film
near the interface. Inset A is the corresponding FFT. Inset
B represents the atomic lattice of the crystalline matrix
(a). The HREM image with an off-structural inclusion
designated by area A. Inset is the FFT of area A (b).
D
B
AA LCM2
B
LAO
3 nm c
a
Fig. 4. Cross-sectional HREM image of the LCM3 film
near the interface. Inset A is the corresponding FFT. Inset
B represents the atomic lattice of the film.
demonstrates a diamagnetic behavior, introduced by
LAO. The measurements performed reveal that the
diamagnetic contribution is about – 3.3·10 �3 emu/g
for all the prepared films. This contribution was first
subtracted from the magnetization curves for the ana-
lyses. Figure 5,b shows that the M(T) dependence for
the LCM2 film represents a superposition of two con-
tributions: the well-defined FM transition at
TC � 260K, and the paramagnetic term which is man-
ifested by a rapid increase of the M( T) at T � 0.
Taking into account the XRD and HREM data, one
can conclude that the FM phase belongs to the crystal-
line matrix and the PM phase corresponds to the
nanocrystalline inclusions. Figure 5,c shows that the
crystalline LCM3 film undergoes only a FM transition
at TC � 204 K, which is lower than that for LCM2
and can be explained by the generated lattice strains
in the film [17]. The inset in Fig. 5,c presents the hys-
teresis loop of the magnetization, measured at 5 K, for
the LCM3 film. It is seen that the magnetization is
saturated at Hs � 9000 Oe and that the coercive field
is about 500 Oe. The carried out analysis shows that
the saturation magnetization does not exceed of 2.73
�B/Mn that is typical for the lattice strained thin
films [16] and is much smaller than observed for the
bulk, 3.5 �B /Mn [17].
Figure 6 displays the temperature dependence of
the resistance, R(T), for the LCM3 film with (solid)
and without (open) an applied magnetic field of 5 T.
Unfortunately, our setting was limited to 107 �, and
the R T( ) could not be measured for LCM1 and LCM2,
since their resistances are about 1012 and 107 � at
room temperature, respectively. The magnetic field
was directed parallel to the film surface and at a right
angle to the transport current. The metal–insulator
(MI) transition is observed at TP � 180 K and is
much lower than TC. Inset A in Fig. 6 shows the tem-
perature dependence of the MR for the same film. 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, respectively. It is seen that the
MR(T) dependence has a peak-like shape and reaches
almost 1500% at the maximum.
Magnetic and transport properties films controlled by structural disorder in La07. Ca03. MnO3
Fizika Nizkikh Temperatur, 2004, v. 30, No. 9 941
0.5
1.0
T
C
a
1
2
3
T
C
b
50 100 150 200 250
0
20
40
60
TC
c
T, K
1 2 3 4
–10
–5
0 300 K
H, kOe
–1 0 1
–0.5
0
0.5
5 K
H, T
M
,1
0
e
m
u
/g
–
5
M
,e
m
u
/g
M
, 1
0
e
m
u
/g
–
5
Fig. 5. Field-cooled (solid) and zero-field-cooled (open)
magnetization curves for the LCM1 (a), LCM2 (b), and
LCM3 (c) films. The inset in (a) displays the field-depend-
ent magnetization at 300 K for LCM1. The inset in (c)
shows the hysteresis loop at 5 K for LCM3. The dashed
lines are the theoretical curves, based on the mean-field ap-
proximation for ferromagnetic materials. The lines are
guides to the eye.
50 100 150 200 250
10
10
10
T
P
R
,
�
T, K
150 200 250
0.4
0.8
1.2
A
T, K
3
1
10
0.5 1
B
lg(m–m )0
lg
(1
/
)
M
R
,1
0
%
4
3
2
Fig. 6. Temperature dependence of the resistance for
LCM3 film without (open) and with (solid) an applied
magnetic field of 5 T. The lines are guides to the eye. In-
set A shows the temperature dependence of the MR ratio
in an applied magnetic field of 5 T. Inset B displays the
lg versus lg( / ) (1 m � m0) plot with the slope correspond-
ing to the percolation exponent t � 5.7.
5. Discussion
As above-mentioned, the amorphous LCM1 film
demonstrates mainly paramagnetic M(T) behavior
with a trace of FM. Thus, the expression for the total
magnetization of LCM1 can be written as M(T H, ) =
� MPM(T H, )
MFM(T H, ). The paramagnetic con-
tribution to the magnetization could be written, in the
whole temperature range, as [16]
M T H
C
T
HPM CW( , ) ,�
�
�
�
�
��
�0 (1)
where �0 is the temperature-independent susceptibility,
and the second term is a Curie–Weiss (CW)-type sus-
ceptibility with a constant CCW and a characteristic
temperature �. Figure 7,a demonstrates that the experi-
mental data for LCM1 is excellently described by the
CW expression with the following fitting parameters:
�0 � 2.5�10�4 cm3/g, CCW � 1.04�10�2 cm3/g, and
� = 3 K. The estimated from CCW effective moment
turn out to be � eff � 4.2 �B/Mn, that is almost coin-
cident with the theoretical value, �eff
theo
� 4.6 �B/Mn,
which is obtained from the following expression:
�eff
theo �
�
g xS S x S S1 1 2 21 1 1( ) ( ) ( ). (2)
Here x is the Ca concentration, S1 = 3/2 and S2 = 2
are the spin values of Mn4
and Mn3
ions, respec-
tively, and g = 2 is the Lande factor. Therefore, one
can conclude that the amorphous LCM1 film is
mainly a typical CW-type paramagnet. On the other
hand, the magnetization decreases sharply and devi-
ates from a straight line in the range of small values
for T �1 (T � 130–150 K), as denoted by an arrow in
Fig. 7,a. It is reasonable to suggest that the observed
deviation from the CW law is governed by the FM
transition of the crystalline interfacial layers. The
mean-field theory gives the following temperature de-
pendence of the spontaneous magnetization for a fer-
romagnet below TC[16]:
M
M
M
M
T
T
H
M T
FM
FM
FM
FM
C
FM
0 0 0
� �
�
�
�
�
�
�
�
�
tanh diff�
, (3)
where MFM
0 is the spontaneous magnetization at
T � 0 and �diff is the differential susceptibility. The
dashed lines in Figs. 5,a,b, and 5,c are the theoretical
curves calculated in the mean-field approximation.
�diff � 2.19�10 �4 cm3/g was taken from the magneti-
zation hysteresis loop for LCM3 (see inset in Fig. 5,c,)
which is already in the FM state at a magnetic field
of 100 Oe.
Figure 7,b shows the M T H H T( , ) versus plot for
the LCM2 film, measured at H = 100 Oe, and the inset
presents the same plot at H = 2 kOe. It is seen that the
experimental curves cannot be described by the CW
approximation, since they do not demonstrate a linear
behavior in the whole temperature range. Such a
nonlinearity of the M(H T) is more typical for super-
paramagnetic (SPM) particles and can be described
by the Langevin function [16]:
M T H M
H
k T
k T
H
SPM
s
SPM
B
B( , ) ,�
�
�
�
�
�� �
�
�
�
�
�
�coth
�
� (4)
where Ms
SPM is the saturation magnetization of the
SPM phase and � is the average magnetic moment of
the SPM particles. The solid lines represent the
Langevin functions fitted closest to the experimental
data. These lines correspond to an average magnetic
moment of the SPM particles of 3000�B at H = 100
Oe and 800�B at H = 2 kOe. By taking 3.5�B/Mn
atom [18] and assuming a spherical shape of the SPM
clusters with a volume of �D3 6, where D is the ave-
rage diameter, we estimate their average diameter to
942 Fizika Nizkikh Temperatur, 2004, v. 30, No. 9
V.G. Prokhorov, V.A. Komashko, G. G. Kaminsky, V.L. Svetchnikov, Y.P. Lee, and S.Y. Park
2 4 6 8 10
0
5
10
a
2 4 6 8 10
2
3
4
5 b
H/T, 10 kOe/K
5 10
0
1
2
H = 2 kOe
H/T, 10 kOe/K
T,–1 10 K–2
M
,1
0
e
m
u
/g
–
3
M
,1
0
e
m
u
/g
–
4
M
, 1
0
e
m
u
/g
–
3
–3
–2
–1
Fig. 7. M versus T�1 plot for the LCM1 film at H =
= 100 Oe. The solid line represents the CW-type paramag-
netic approximation. The arrow indicates the deviation of
the experimental curve from the CW-type straight line,
reflecting the presence of a FM phase (a). M versus
H T/ plot for the LCM2 film at H = 100 Oe. The solid
line represents a Langevin function describing the mag-
netic behavior of superparamagnetic particles. The arrow
indicates the presence of a FM phase. The inset is the
same plot at H = 2 kOe (b).
be D � 5 nm for 100 Oe and � 3 nm for 2 kOe.
Analysis of the HREM images (see Fig. 3,b) shows
that the randomly-oriented crystallites in inclusions
have a similar size to this estimation for the SPM
clusters. Therefore, one can conclude that nanocrys-
talline clusters play the role of the SPM particles in
this film. The observed decrease in the average mo-
ment of the SPM particles in an applied magnetic
field can be explained by a partial SPM to FM transi-
tion due to an enhancement of the ferromagnetic cou-
pling between adjacent nanocrystalline clusters. It is
provided by a high conductive transparency of bound-
aries in the such type of a nanocrystalline mosaic
structure. In this case the arrangement of magnetic
moments in the increasing field can lead to a recovery
of the double exchange interaction between neighbor-
ing crystallites.
As already described, the observed decrease in TC
for the LCM3 film is explained by an influence of the
lattice strain which was accumulated in the film dur-
ing the epitaxial growth. For weaker strains and a cu-
bic symmetry, the Curie point can be expressed, ac-
cording to Millis model, by [17]
T TC C B JT(º) (º ) º º ,� � � ��
�
�
�
�0 1
1
2
2� � (5)
where º ( º º )B �
2 100 001 is the bulk strain, ºJT �
� �2 3 001 100(º º ) is the Jahn–Teller strain, � �
� ( )( º )1 T dT dC C B , and � � ( )( )1 2 2T d T dC C JT� .
The magnitudes of � and � represent the relative
weights for symmetry-conserving bulk and symme-
try-breaking Jahn–Teller strains, respectively. Ac-
cording to the theoretical model, [17] � � 10 for a
reasonable electron–phonon coupling (0.5 � �� 1) in
these compounds. Taking into account that the Curie
temperature for the strain-free bulk La07. Ca03. MnO3
compound is TC( )� � 0 � 265 K [14,19] and using
the obtained values of �100 and �001 and TC for
LCM3, we determined � to be about 950, which is of
the same order of magnitude as the prediction of the
theoretical model [17]. A possible explanation for
this discrepancy is that the lattice mismatch between
LCM3 and LAO is so large that the effect of struc-
tural disorder becomes dominant over the strain effect
and that the role of Jahn–Teller distortion in forma-
tion of the ferromagnetic ordering is distinctly de-
creased. On the other hand, the additional deforma-
tion of the crystal lattice can be connected with the
so-called «chemical-pressure» effect which is pro-
vided by the high diffusion rate of oxygen in these
materials. Therefore, the modified lattice parameters
are caused by both the simple elastic strain and the
nonstoichiometry. In any case, the obtained results
reflect a strong correlation between crystal lattice
distortion and the electronic and magnetic states in
CMR materials.
According to percolation theory, the conductivity can
expressed as � � �( )p p t
0 , where p is the concentra-
tion of a metallic phase and p0 is its critical value [20].
Taking into account that the value of the spontaneous
magnetization is proportional to the concentration of the
FM metallic phase and p0 = 0.395 for three-dimensional
systems [21], we can express the percolating conductiv-
ity for LCM3 by the formula ( )1 � (m m� 0)t , where
� R T R TP( ) ( ), R TP( ) is the resistance at temperature
of the MI transition, m M T M� ( ) ( )0 , and m0 = 0.395.
Inset B in Fig. 6 exhibits a linear dependence of
lg versus( )1 lg ( )m m� 0 , and the slope of the
curve corresponds to the exponent t � 5.7. This ex-
perimental value for t is very close to that (t � 5.3)
obtained by a numerical calculation for the three-di-
mensional system, considering the spin effects [21].
Therefore, one can conclude that the MI transition in
the LCM3 film has a percolating nature. It is reason-
able to suggest that the nonuniformly distributed lat-
tice strains in the film play a key role in blocking the
complete transition to the FM phase within a narrow
temperature range.
6. Conclusion
In summary, La07. Ca03. MnO3 films were success-
fully prepared to have three characteristic structures:
amorphous, a strain-free crystalline (with ran-
domly-oriented nanocrystalline mosaic inclusions) and
lattice-strained crystalline, and their the magnetic pro-
perties were investigated. It was shown that the amor-
phous film exhibits a CW-type PM behavior with a
freely moving of the individual Mn spins and a small
FM contribution governed by the quasi-two-dimen-
sional crystalline interfacial phase. The crystalline film
with nanocrystalline mosaic inclusions demonstrates a
superposition of the FM (corresponding to the crystal-
line matrix) and the SPM (to the nanocrystalline mo-
saic inclusions) contributions. The fitted average size of
SPM particles using Langevin function is coincident
with that of the nanocrystalline mosaic clusters repre-
sented by the HREM images. An increase in the ap-
plied magnetic field leads to a reduction in the average
magnetic moment of SPM particles, which is due to an
enhancement of the FM coupling between the individ-
ual crystallites in a mosaic inclusions and a partial
SPM to FM transition. The observed suppression of
contribution from the Jahn–Teller distortion to the FM
ordering, with increasing the lattice mismatch between
substrate and lattice-strained film, manifests a physical
limit of the small-strain approach [17] in describing the
magnetic properties of manganite films.
Magnetic and transport properties films controlled by structural disorder in La07. Ca03. MnO3
Fizika Nizkikh Temperatur, 2004, v. 30, No. 9 943
This work was supported by the KOSEF through
the Quantum Photonic Science Research Center.
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