Magnetic and transport properties of La₀.₇Sr₀.₃MnO₃/Pr₀.₆₅Ca₀.₃₅MnO₃ multilayered films with different microstructure
The magnetic and transport properties of single-crystal and polycrystalline La₀.₇Sr₀.₃MnO₃/Pr₀.₆₅Ca₀.₃₅MnO₃ multilayered films are investigated in the temperature range 4.2–300 K. It is shown that the transformation from an incoherent to a coherent interface between layers leads to an enhance...
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| Zitieren: | Magnetic and transport properties of La₀.₇Sr₀.₃MnO₃/Pr₀.₆₅Ca₀.₃₅MnO₃ multilayered films with different microstructure / V.G. Prokhorov, V.S. Flis, G.G. Kaminsky, Y.P. Lee // Физика низких температур. — 2004. — Т. 30, № 6. — С. 619-625. — Бібліогр.: 30 назв. — англ. |
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irk-123456789-1197372017-06-09T03:04:30Z Magnetic and transport properties of La₀.₇Sr₀.₃MnO₃/Pr₀.₆₅Ca₀.₃₅MnO₃ multilayered films with different microstructure Prokhorov, V.G. Flis, V.S. Kaminsky, G.G. Lee, Y.P. Низкотемпеpатуpный магнетизм The magnetic and transport properties of single-crystal and polycrystalline La₀.₇Sr₀.₃MnO₃/Pr₀.₆₅Ca₀.₃₅MnO₃ multilayered films are investigated in the temperature range 4.2–300 K. It is shown that the transformation from an incoherent to a coherent interface between layers leads to an enhancement of the ferromagnetic coupling, which is accompanied by a modification in the temperature dependence of the resistance and by a grown negative magnetoresistance ratio at room temperature. The influence of grain boundaries on the transport of carriers in the multilayered films is discussed on the basis of modern theoretical approaches. 2004 Article Magnetic and transport properties of La₀.₇Sr₀.₃MnO₃/Pr₀.₆₅Ca₀.₃₅MnO₃ multilayered films with different microstructure / V.G. Prokhorov, V.S. Flis, G.G. Kaminsky, Y.P. Lee // Физика низких температур. — 2004. — Т. 30, № 6. — С. 619-625. — Бібліогр.: 30 назв. — англ. 0132-6414 PACS: 71.30.+ h, 75.47.Gk, 75.47.Lx http://dspace.nbuv.gov.ua/handle/123456789/119737 en Физика низких температур Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine |
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English |
| topic |
Низкотемпеpатуpный магнетизм Низкотемпеpатуpный магнетизм |
| spellingShingle |
Низкотемпеpатуpный магнетизм Низкотемпеpатуpный магнетизм Prokhorov, V.G. Flis, V.S. Kaminsky, G.G. Lee, Y.P. Magnetic and transport properties of La₀.₇Sr₀.₃MnO₃/Pr₀.₆₅Ca₀.₃₅MnO₃ multilayered films with different microstructure Физика низких температур |
| description |
The magnetic and transport properties of single-crystal and polycrystalline
La₀.₇Sr₀.₃MnO₃/Pr₀.₆₅Ca₀.₃₅MnO₃ multilayered films are investigated in the temperature range
4.2–300 K. It is shown that the transformation from an incoherent to a coherent interface between
layers leads to an enhancement of the ferromagnetic coupling, which is accompanied by a modification
in the temperature dependence of the resistance and by a grown negative magnetoresistance ratio
at room temperature. The influence of grain boundaries on the transport of carriers in the multilayered
films is discussed on the basis of modern theoretical approaches. |
| format |
Article |
| author |
Prokhorov, V.G. Flis, V.S. Kaminsky, G.G. Lee, Y.P. |
| author_facet |
Prokhorov, V.G. Flis, V.S. Kaminsky, G.G. Lee, Y.P. |
| author_sort |
Prokhorov, V.G. |
| title |
Magnetic and transport properties of La₀.₇Sr₀.₃MnO₃/Pr₀.₆₅Ca₀.₃₅MnO₃ multilayered films with different microstructure |
| title_short |
Magnetic and transport properties of La₀.₇Sr₀.₃MnO₃/Pr₀.₆₅Ca₀.₃₅MnO₃ multilayered films with different microstructure |
| title_full |
Magnetic and transport properties of La₀.₇Sr₀.₃MnO₃/Pr₀.₆₅Ca₀.₃₅MnO₃ multilayered films with different microstructure |
| title_fullStr |
Magnetic and transport properties of La₀.₇Sr₀.₃MnO₃/Pr₀.₆₅Ca₀.₃₅MnO₃ multilayered films with different microstructure |
| title_full_unstemmed |
Magnetic and transport properties of La₀.₇Sr₀.₃MnO₃/Pr₀.₆₅Ca₀.₃₅MnO₃ multilayered films with different microstructure |
| title_sort |
magnetic and transport properties of la₀.₇sr₀.₃mno₃/pr₀.₆₅ca₀.₃₅mno₃ multilayered films with different microstructure |
| publisher |
Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України |
| publishDate |
2004 |
| topic_facet |
Низкотемпеpатуpный магнетизм |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/119737 |
| citation_txt |
Magnetic and transport properties of La₀.₇Sr₀.₃MnO₃/Pr₀.₆₅Ca₀.₃₅MnO₃ multilayered films with different microstructure / V.G. Prokhorov, V.S. Flis, G.G. Kaminsky, Y.P. Lee // Физика низких температур. — 2004. — Т. 30, № 6. — С. 619-625. — Бібліогр.: 30 назв. — англ. |
| series |
Физика низких температур |
| work_keys_str_mv |
AT prokhorovvg magneticandtransportpropertiesofla07sr03mno3pr065ca035mno3multilayeredfilmswithdifferentmicrostructure AT flisvs magneticandtransportpropertiesofla07sr03mno3pr065ca035mno3multilayeredfilmswithdifferentmicrostructure AT kaminskygg magneticandtransportpropertiesofla07sr03mno3pr065ca035mno3multilayeredfilmswithdifferentmicrostructure AT leeyp magneticandtransportpropertiesofla07sr03mno3pr065ca035mno3multilayeredfilmswithdifferentmicrostructure |
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2025-07-08T16:30:36Z |
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2025-07-08T16:30:36Z |
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| fulltext |
Fizika Nizkikh Temperatur, 2004, v. 30, No. 6, p. 619–625
Magnetic and transport properties
of La0.7Sr0.3MnO3/Pr0.65Ca0.35MnO3 multilayered films
with different microstructure
V.G. Prokhorov, V.S. Flis, and G.G. Kaminsky
Institute of Metal Physics, National Academy of Sciences of Ukraine
36 Vernadskogo Ave., Kiev, 03142, Ukraine
Email: pvg@imp.kiev.ua
Y.P. Lee
Quantum Photonic Science Research Center and Department of Physics
Hanyang University, Seoul, 133–791 Korea
Received October 29, 2003, revised December 19, 2003
The magnetic and transport properties of single-crystal and polycrystalline
La Sr MnO Pr Ca MnO0.6507 03 3 035 3. . ./ multilayered films are investigated in the temperature range
4.2–300 K. It is shown that the transformation from an incoherent to a coherent interface between
layers leads to an enhancement of the ferromagnetic coupling, which is accompanied by a modifica-
tion in the temperature dependence of the resistance and by a grown negative magnetoresistance ra-
tio at room temperature. The influence of grain boundaries on the transport of carriers in the multi-
layered films is discussed on the basis of modern theoretical approaches.
PACS: 71.30.+ h, 75.47.Gk, 75.47.Lx
The hole-doped perovskite manganites,
R A MnO1 3�x x (R = rare-earth cation, A = alkali or al-
kaline-earth cation), have attracted considerable atten-
tion due to not only their interesting fundamental sci-
ence, partly connected with the discovery of colossal
magnetoresistance (CMR), but their potential for de-
vice applications [1,2]. Most of the early theoretical
works on manganites focused on the relation between
the transport and magnetic properties and explained
the coexistence of ferromagnetism and metallic behav-
ior within the framework of a «double exchange» (DE)
model, which considers the magnetic coupling between
Mn3� and Mn4+ that results from the motion of an
electron between two partially filled d shells with
strong on-site Hund’s coupling [3–5]. In spite of con-
siderable scientific efforts, however, the complex inter-
play between the charge, lattice, spin, and orbital de-
grees of freedom in these systems is not completely
understood. The situation is further complicated by the
fact that the magnetic and transport properties are de-
pendent significantly on the cation size, the lattice
strain, and the microstructure. Recently it was found
that the presence of grain boundaries (GBs) in the
polycrystalline manganites leads to a large MR effect
over a wide temperature range below the Curie temper-
ature TC, whereas the CMR in the single-crystal mate-
rials is restricted to a narrower temperature range just
around TC [6–8].
The most widely different manganite compounds
were chosen for fabrication of the multilayer structure
in this work: Pr Ca MnO065 035 3. . (PCMO) and
La Sr MnO07 03 3. . (LSMO). The first of them remains
insulator in both the paramagnetic and ferromagnetic
states [9] (or displays an incomplete metal-insulator
(MI) transition in the lattice-strained state [10]), and
the second one shows a metal-like behavior of electri-
cal resistance in the whole temperature range [11]. In
spite of the fact that TC of LSMO exceeds room tem-
perature, this compound manifests insignificant
changes in resistance in applied magnetic fields owing
to a small value of the intrinsic resistivity in the me-
tallic state. It can be expected that the presence of
high-resistance PCMO layers can lead to an enhan-
cement of the magnetoresistance effect in the
© V.G. Prokhorov, V.S. Flis, G.G. Kaminsky, and Y.P. Lee 2004
PCMO/LSMO multilayered films. Recently it was
reported that the substitution of the small-size Pr ion
by La in the compound Pr Ca MnO067 033 3. . leads to the
appearance of a MI transition at low temperature ow-
ing to the melting of a charge-ordered insulating state
[12]. On the other hand, the substitution of Sr for Ca
in Pr Ca Sr MnO07 03 3. . �x x induces the formation of a
low-temperature metallic state, as well [13].
In this paper we report experimental results concern-
ing the magnetic and transport properties
of Pr Ca MnO La Sr MnO PCMO LSMO0.35 0.30 65 3 0 7 3. . ( )/ /
multilayered (ML) films prepared by laser ablation on
single-crystal LaAlO3 (SC) and polycrystalline Al O2 3
(PC) substrates at two different temperatures, Tsub �
= 560 and 710 �C. The low Tsub were used for prepara-
tion of the ML films to avoid chemical interaction be-
tween layers. In the first case, high-textured ML films
(which will be denoted by SC) were fabricated with a
coherent and an incoherent interface between layers,
which was controlled by Tsub. In the second case,
polycrystalline ML films were obtained. It was shown
that the transformation from an incoherent to a coher-
ent interface between layers leads to an enhancement of
the ferromagnetic coupling in the SCML films. This
process is accompanied by a modification in the temper-
ature dependence of resistance from R T� 3 to � T 45.
and has been attributed to transition from one- to
two-magnon–electron scattering. The PCML films
demonstrate the R T� 2 behavior, which is explained
by the interference between the elastic electron scatter-
ing on GBs and the electron–magnon scattering. The
exponential growth of resistance at low temperature,
R T E /T( ) exp� C , has its origin in a small Coulomb
barrier which formed on the GBs. The MR ratio of the
PCML films is dominated by a spin-polarized tunneling
between grains. It was shown that the model of two pa-
rallel resistances can be used for a simulation of the
transport properties in the ML films.
1. Experimental details
A pulsed-laser-deposition method was employed for
the preparation of the films. We used two Nd-YAG la-
sers with a wavelength of 1064 nm, a pulse duration of
7.8–10.5 ns, and an energy of 0.3 J/pulse. The film de-
position was carried out at a pulse repetition rate of
20 Hz. The power density of a laser beam focused on
the target was 9.5·108–2·1010 W/cm2. The targets
were fabricated from the Pr Ca MnO0.35065 3. and
La Sr MnO07 03 3. . powders of the stoichiometric com-
position by hot-pressing and heating at 1200 �C for
4 days in air. The oxygen pressure in chamber was
200 Torr during deposition and 600 Torr during cooling.
Under these conditions we grew the ML films on
LaAlO3(100) single-crystal and Al2O3 polycrystalline
substrates at different temperatures, Tsub C� 560 � and
710 �C. The ML films contain six LSMO and five
PCMO layers with LSMO at the top and the bottom.
The thickness of each layer was � 20 nm.
The �–2� x-ray diffraction (XRD) patterns were
obtained using a Rigaku diffractometer with Cu K�1
radiation. The lattice parameters evaluated directly
from the XRD data were plotted against cos sin2 � �/ .
With an extrapolated straight line to cos sin ,2 0� �/ �
a more precise determination of the lattice parameter
was obtained. The resistance measurements were per-
formed by using the standart four-probe method. The
temperature dependence of the field-cooled (FC) and
the zero-field-cooled (ZFC) in-plane magnetization at
a magnetic field of 100 Oe was taken with a Quantum
Design SQUID magnetometer.
2. Results and discussion
Structure
Figure 1,a presents the �–2� XRD scans for two
ML films deposited on LaAlO3 at Tsub C� 560 �
(SCML1) and 710 °C (SCML2). SCML1 and SCML2
are the multilayred film deposited on the single-crys-
tal LaAlO3 substrate at 560 °C and 710 °C, respec-
tively. High intensities of the (00l) peaks attest that
the deposition results in highly c-oriented films.
620 Fizika Nizkikh Temperatur, 2004, v. 30, No. 6
V.G. Prokhorov, V.S. Flis, G.G. Kaminsky, and Y.P. Lee
a
LS
M
O
P
C
M
O
46.5 47.0 47.546.0
2 , deg�
In
te
n
si
ty
, 1
0
c
p
s
3
2
1
b4
3
2
1
(002)
30 40 50 60 70
LA
O
LA
O
LA
O
M
L
M
L
M
L
(0
0
1
)
(0
0
2
)
(0
0
3
)
In
te
n
si
ty
, c
p
s
10 4
103
10
2
101
Fig. 1. (a) XRD patterns of the SCML films. LAO and
ML denote the diffraction peaks from the substrate and
the film itself, respectively. (b) The (002) diffraction
peaks for the SCML1 (1) and the SCML2 (2) films.
Figure 1,b is the (002) Bragg peaks for the SCML1
(curve 1) and SCML2 (curve 2) films, respectively. It
is seen that the decrease in Tsub leads to a shift of the
Bragg peak towards a larger angle. In addition to the
decrease in out-of-plane lattice parameter, the SCML1
film displays a kink-like peculiarity in the (002) peak,
which can be interpreted as the presence of different
crystalline phases with the following out-of-plane lat-
tice parameters: c� 0.3877 and 0.3848 nm. To show
this more clearly, Fig. 1,b includes a fitting to the
split (002) peak by using two Lorentzian functions
(dashed lines). The first lattice parameter is almost
coincident with that for the bulk LSMO single crys-
tal, ac = 0.3876 nm [11], while the second one is simi-
lar to the average lattice parameter of the bulk PCMO
compound, � �ac � 0.3843 nm [14], for the cubic sym-
metry. The SCML2 film displays only the unsplit
Bragg peak which corresponds to c � 0.3903 nm.
Therefore, one can conclude that at a low Tsub the
PCMO and the LSMO layers form an incoherent in-
terface and have different lattice parameters close to
those of the respective bulk materials. An increase in
Tsub provides an enhancement of the epitaxial growth
process and induces the formation of a coherent inter-
face between layers in the SCML2 film. The ML films
deposited on polycrystalline Al O2 3 (PCML) exhibit
the multipeak XRD patterns of very weak intensity,
which are beyond an analysis.
Magnetic properties
Figures 2,a and 2,b present the temperature depen-
dence of FC and ZFC magnetization, M(T), for
SCML1 (curve 1) and SCML2 (curve 2), and PCML1
(curve 1) and PCML2 (curve 2), respectively. PCML1
and PCML2 are the multilayered films deposited on
the polycrystalline Al O2 3 substrate at Tsub C� 560 �
and 710 �C, respectively. The SCML1 film (curve 1 in
Fig. 2,a) demonstrates an M(T) dependence, which is
typical for two-phase magnetic systems, and represents
a superposition of two magnetic transitions for the
PCMO layers at TC2 K 130 [10] and for the LSMO
layers at TC1
300 K [15]. Moreover, the absolute
value of the magnetization at low temperatures is
almost twice greater than that at T T
C2. This is
evidence for independent magnetic transitions in six
LSMO and in five PCMO layers, and for a lack of fer-
romagnetic coupling between them. We are claiming
that the main reason for a suppression of the magnetic
coupling between layers in this film is the aforemen-
tioned incoherence of their interfaces. The increase of
Tsub leads to the conversion into a coherent interface
and thus to the appearance of a ferromagnetic coupling
between two kinds of layers. The SCML2 film displays
a monotonic M(T) dependence (curve 2 in Fig. 2,a)
without any peculiarity at TC2 which is relevant to the
magnetic transition for the PCMO layers. Figure 2,b
shows that a similar transformation in the magnetic
state governed by the substrate temperature is also
typical for the PCML films. The PCML1 film mani-
fests a kink-like peculiarity at TC2 on both FC and ZFC
M T( ) curves (curve 1 in Fig. 2,b), although the magni-
tude is greatly smaller than that observed for the
SCML1 film. The increase of Tsub leads to a degrada-
tion of the peculiarity (curve 2 in Fig. 2,b). A similar
ferromagnetic coupling was observed recently in
La Sr MnO La Sr MnO La Ca MnO055 0 45 3 09 01 3 067 033 3. . . . . .( )/
multilayered films prepared at a high temperature of
substrate [16].
Therefore, one can conclude that the ferromagnetic
coupling between layers in multilayered films is con-
trolled by the coherence ratio of their interfaces.
Transport properties
Figure 3 shows the temperature dependence of resis-
tance R(T) for the SCML1 (curve 1) and the SCML2
(curve 2) films without (solid symbols) and with (open
symbols) an applied magnetic field of 5 T. The mag-
netic field was parallel to the film surface and normal
to the transport current. The change in the magnetic
field direction does not transform the R(T) behavior.
The experimental curves testify that the resistance peak
TP in the investigated temperature range is observed
only for the SCML1 film (curve 1). A similar tempera-
Magnetic and transport properties of La Sr MnO PrCa MnO07 03 3 035 3. . ./
Fizika Nizkikh Temperatur, 2004, v. 30, No. 6 621
5
10
15
TC1
ZFC
FC
a
TC2
2
1
100 200 300
TC1
ZFC
FC
b
1
2
TC2
T, K
1
0
e
m
u
–
4
M
, 25
20
15
10
5
Fig. 2. (a) Temperature dependence of FC (solid) and
ZFC (open) magnetization for the SCML1 (1) and the
SCML2 (2) films. (b) The same for the PCLM1 (1) and
the PCML2 (2) films.
ture behavior of resistance was observed recently for
La Ca MnO Pr Ca MnO2 3 1 3 3 2 3 1 3 3/ / / // multilayered
films with a sublayer thickness of 10 nm, but at a lower
temperature [17]. The SCML2 film (curve 2) demon-
strates a metallic-like behavior of the R(T) in the whole
investigated temperature range. Inset in Fig. 3 shows
the temperature dependence of the magnetoresistance
ratio. The MR value is defined by 100% � �[ ( )R 0
�R H /R( ) ( )0 , where R(0) and R H( ) are the resistance
with and without a magnetic field of 5 T, respectively.
It is seen that for SCML1 (curve 1) MR(T) shows the
nonmonotonic dependence with a peak at T � 200 K,
while the MR(T) of SCML2 increases monotonically
with temperature and reaches almost 60% at room tem-
perature, which is much greater than that ever ob-
served for the bare LSMO film [18].
Figure 4 displays the temperature dependence of
resistance for the PCML1 (curve 1) and the PCML2
(curve 2) films without (solid symbols) and with (open
symbols) an applied magnetic field of 5 T. It is seen that
theR(T) behavior of the PCML films differs significantly
from that of the SCML ones. Inset in Fig. 4 shows that in
contrast to the single-crystal ML films the MR value for
the PCML films is minimum at room temperature and in-
creases with decreasing temperature.
Single-crystal multilayered films. First of all, let us
consider the R(T) behavior of SCML films. Figure 3
(curve 1) shows that the MI transition in the SCML1
film (TP � 260 K) occurs at a temperature below the
Curie point (TC � 300 K). As a rule, the temperature dif-
ference between the magnetic and electronic transitions in
CMR compounds is explained by an intrinsic
inhomogeneity of these materials and by a percolative na-
ture of the conductivity [19]. On the other hand, a more
simplified explanation can be employed in our case. Re-
cently the two parallel resistor model was used for de-
scription of the transport properties of bi- and trilayers
La Sr MnO La Sr MnO055 0 45 3 067 033 3. . . ./ films [20]. The
equivalent resistance for the SCML film can be described
by R T� �1( ) R TPCMO
�1 ( ) + R TLSMO
�1 ( ), where
R TPCMO( ) and R TLSMO( ) are the total resistances of
the PCMO and the LSMO layers, respectively. There-
fore, the resistance of the multilayered film is determined
by the electron transport in PCMO at high temperature
(R RPCMO LSMO�� ) or in LSMO at low temperature
( )R RLSMO PCMO�� . The R TPCMO( ) behavior can be
approximated by the usual Arrhenius form, which is typi-
cal for the bare PCMO films [10] and is provided by a
polaron motion [2,21]: R T R T T /TAPCMO( ) exp( )� 0 ,
where TA is the activation energy in units of temperature.
The RLSMO(T) behavior can be obtained directly from
the low-temperature part of the experimental R(T) de-
pendence. The inset in Fig. 5 shows that for the LSMO
layers, R TLSMO( ) � R T1
3� � for SCML1 and
622 Fizika Nizkikh Temperatur, 2004, v. 30, No. 6
V.G. Prokhorov, V.S. Flis, G.G. Kaminsky, and Y.P. Lee
50 100 150 200 250 300
0
20
40
60
80
100
TP
21
T, K
100 200 300
20
40
60
2
1
T, K
R
,
M
R
%
,
Fig. 3. Temperature-dependent resistance of the SCML1
(1) and SCML2 (2) films, measured in a magnetic field of
zero (solid) and 5 T (open). The inset displays the MR
ratio in a perpendicular magnetic field of 5 T. The solid
lines are drawn to guide the eye.
100 200 300
1
10
TP
TP
2
1
T, K
100 200
25
50
2
1
T, K
R
k
, M
R
%
,
Fig. 4. Temperature-dependent resistance of the PCML1
(1) and the PCML2 (2) films, measured in a magnetic
field of zero (solid) and 5 T (open). The inset displays the
MR ratio in a perpendicular magnetic field of 5 T. The
solid lines are drawn to guide the eye.
R TLSMO( ) = R T2
45� � . for SCML2 with the following
fitting parameters: R1 15�
, � � � �� �6 5 10 6 3.
K ,
R2 4 5� .
, and � � � �� �6 10 10 45
K . . According to
theoretical models, the T3 term in the resistance corre-
sponds to the one-magnon–electron scattering [22], while
the T 45. term reflects the two-magnon–electron scatter-
ing processes [23]. Therefore, the electron–magnon scat-
tering is dominating for the LSMO layers in the SCML
films and transforms from one- to two-magnon scattering
with an enhancement of the ferromagnetic coupling be-
tween layers. The solid lines in Fig. 5 display the theoret-
icalR T( ) curves, which were calculated in the framework
of the two parallel resistor model with the use of the
previous fitting parameters for the LSMO layers, and
R0
3 110�
� ��
K and TA = 2600 K for the PCMO la-
yers. It is seen that the theoretical curves agree excel-
lently with the experimental data.
Polycrystalline multilayered films. Figure 4 shows
that the R(T) behavior for the PCML films is very
different from that for the SCML ones, exhibiting a
wide maximum at temperature well below TC and a
minimum at Tmin � 30–40 K. The temperature de-
pendence of the MR ratio is very close to that for fer-
romagnetic tunnel junctions [24]. The similar pecu-
liarities in the transport properties are typical for the
polycrystalline doped manganites and are explained
by the presence of the grain boundaries [2,8,25,26].
The GBs can play two roles in the mechanism of the
transport of carriers — first as a network of magnetic
tunnel junctions and second as additional centers for
the elastic electron scattering in a metal-like channel of
conductivity. First of all, let us consider the R(T) be-
havior of the PCML films in the metal-like state
( )minT T T� � P and discuss the influence of GBs on
the transport properties. Figure 6,a shows that in this
temperature range R T T( ) � 2 for both of the poly-
crystalline multilayered films instead of T3 and T 45. ,
which were observed for the single-crystal ones (see the
inset in Fig. 5). Moreover, the applied magnetic field
does not change the R(T) behavior fundamentally but
only decreases the slope of the curves slightly. In nu-
merous publications the square term in the tempera-
ture-dependent resistance is explained by a dominant
role of the electron–electron scattering. However, in
our case this explanation is unusable. The insertion of
GBs in the polycrystalline films leads to enhancement
of the impurity (elastic) contribution to the resistance,
only, and all inelastic scattering processes have to
Magnetic and transport properties of La Sr MnO PrCa MnO07 03 3 035 3. . ./
Fizika Nizkikh Temperatur, 2004, v. 30, No. 6 623
50 100 150 200 250 300
20
40
60
80
100
21
T, K
5 10 15
50
100
150
2
1
2 4 6 8
R
,
R
,
3 6 3T, 10 K
4.5 11 4.5T , 10 K
Fig. 5. The comparison of the experimental R T( ) data
(solid symbols) with the theoretical simulation (solid
lines) in the framework of the two-parallel resistance
model for the SCML1 (1) and the SCML2 (2) films. The
inset displays plots: R versus T3 and R versus T45. for the
same films.
5
10
15
2
1
a
10
2
5000 10000 15000
0,2 0,3 0,4
100
10
1
2
1
b
T
–1/2 K
–1/2,
R
k
,
T 2 K 2,
R
k
,
Fig. 6. The R versus T a2( ) and ln( )R versus T b/�1 2 ( ) plots
for the PCML1 (1) and the PCML2 (2) films, respectively.
become weakly defined on the temperature dependence
of the resistance. We assume that the T2 contribution
to the resistance can be attributed to the interference
between the elastic electron scattering on GBs and the
electron–magnon scattering, similar to what was ob-
served in disordered metal films with domination of the
electron–phonon scattering [27].
Figure 6,b displays the ln( )R versus T /�1 2 plot for
both PCML films. This plot exhibits a linear depend-
ence up to Tmin and manifests the exponential growth
of resistance at low temperature, which is described by
the expression R T /T( ) exp� � . It is noteworthy
that a similar expression with � � EC, where EC is
the charging energy, has been predicted for conductiv-
ity in granular metals [28] and used for the explana-
tion of the low-temperature R(T) behavior in ceramic
La Sr MnO2 3 1 3 3/ / manganite with different grain size
[25]. The value of the charging energy estimated from
the slope of the ln( )R versus T /�1 2 plot was
EC � 20 K and � 2.46 K for the PCML1 and
PCML2 films, respectively. Our results are very close
to those obtained for ceramic samples [25], and the
observed difference in EC value for different PCML
films can be explained by the variation of the grain
size. Indeed, the deposition of the manganite films at a
low substrate temperature leads, as a rule, to the for-
mation of a fine-grain structure, and an increase of
Tsub stimulates grain growth. On the other hand,
E e /dC � 2 , where e is the electronic charge and d is
the grain size [28]. Therefore, the observed larger EC
value for the low-Tsub PCML film with respect to the
high-Tsub one is an absolutely expected result.
Taking into account the peculiarities in R T( ) beha-
vior which are governed by the existence of GBs, we
will be again try to describe the temperature-dependent
resistance of the PCML films on the basis of the paral-
lel circuit model, only in this case the total resistance of
the LSMO layers must involve the sum of
R RLSMO GBs� . Figure 7 shows that in the framework
of this approach the nonmonotonic R(T) behavior can
be described with satisfactory accuracy (solid lines in
Fig. 7). We don’t present here the fitting parameters
used because of their multiplicity and the difficulty in
interpretation of the physical meaning. However, the
carried out analysis allows us to conclude that observed
peaks in R(T) are not provided by the Gbs [8] but come
out from the parallel-resistance circuit of the LSMO
and PCMO layers.
The negative MR of the polycrystalline manganites
is dominated by spin-polarized tunneling between
grains owing to a nearly complete polarization of the
electrons [6]. The simplified equation for the MR in
the framework of the spin-polarized tunneling model
[29,30] can be written as
� �MR � � �
JP
k T
m H T m T
B4
02 2[ , ( , )],
where J is an intergrain exchange constant, P is the
electron polarization, and m is the magnetization nor-
malized to the saturation value. The inset in Fig. 7
shows the dependence of the MR versus m2 plot,
where m M T /M� ( ) ( )0 and M T( ) is the FC magneti-
zation of the PCML films presented in Fig. 4,b. It is
seen that the MR ratio is approximately � m2 for the
both polycrystalline films. On the other hand, the
temperature dependence of the MR ratio (see inset in
Fig. 3) is very far from that predicted by this model,
MR � 1/T. This disagreement can be eliminated by
considering the temperature dependence of the spin
polarization calculated within the framework of the
DE approach (see Fig. 1 in Ref. 24).
3. Conclusions
Summarizing, we have studied the magnetic and
transport properties of single-crystal and poly-
624 Fizika Nizkikh Temperatur, 2004, v. 30, No. 6
V.G. Prokhorov, V.S. Flis, G.G. Kaminsky, and Y.P. Lee
5
10
15
20
2
1
0.5 1.0
0,5
2
1
m 2
M
R
T, K
50 100 150 200 250
R
k
,
Fig. 7. The comparison of the experimental R T( ) data
(solid symbols) with the theoretical simulation (solid
lines) in the framework of the two parallel resistance
model for the PCML1 (1) and the PCML2 (2) films, re-
spectively. Inset displays the MR ratio dependence on the
square of the normalized magnetization for these films.
crystalline PCMO/LSMO multilayered films. It was
shown that the single-crystal ML film with an inco-
herent interface between layers manifests the mag-
netic properties typical for a two-phase magnetic sys-
tem. The temperature-dependent resistance of this
film in the ferromagnetic metallic state is proportional
to T3 and has been attributed to the one-mag-
non–electron scattering. The formation of a coherent
interface between layers, owing to the enhancement of
the epitaxial growth mode, leads to the origin of the
ferromagnetic coupling between layers and to the
domination of a T 45. term in R(T), which is typical for
the two-magnon–electron scattering. The negative
MR of the single-crystal ML films, which reaches al-
most 60% at room temperature in an applied magnetic
field of 5 T, is provided by the MI transition in the
LSMO layer near the Curie temperature. The
polycrystalline ML films demonstrate the R T� 2 be-
havior, which is explained by the interference
between the elastic electron scattering on GBs and the
inelastic electron–magnon scattering. The enhan-
cement of the resistance at low temperature,
R T E /T( ) exp� C , has its origin in a small Coulomb
barrier which forms on the GBs. The negative MR of
the polycrystalline ML films is dominated by a
spin-polarized tunneling between grains and can be
described within the framework of the DE model. The
model of two parallel resistances can be used for simu-
lation of the transport properties in the ML films.
This work was supported by the KOSEF through
the Quantum Photonic Science Research Center.
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