Magnetic proximity effect in Pr₀.₅Ca₀.₅MnO₃/La₀.₇Sr₀.₃MnO₃ bilayered films
The magnetotransport properties of Pr₀.₅Ca₀.₅MnO₃/La₀.₇Sr₀.₃MnO₃ bilayer, and Pr₀.₅Ca₀.₅MnO₃ and La₀.₇Sr₀.₃MnO₃ films, deposited on LaAlO₃ (001) substrate by pulse laser deposition have been investigated. The x-ray diffraction and high-resolution electron-microscopy analysis reveals that lattice...
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Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України
2012
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irk-123456789-1167702017-05-16T03:02:37Z Magnetic proximity effect in Pr₀.₅Ca₀.₅MnO₃/La₀.₇Sr₀.₃MnO₃ bilayered films Prokhorov, V.G. Kaminsky, G.G. Flis, V.S. Kim, J.M. Eom, T.W. Park, J.S. Lee, Y.P. Svetchnikov, V.L. Низкотемпеpатуpный магнетизм The magnetotransport properties of Pr₀.₅Ca₀.₅MnO₃/La₀.₇Sr₀.₃MnO₃ bilayer, and Pr₀.₅Ca₀.₅MnO₃ and La₀.₇Sr₀.₃MnO₃ films, deposited on LaAlO₃ (001) substrate by pulse laser deposition have been investigated. The x-ray diffraction and high-resolution electron-microscopy analysis reveals that lattice parameters for the constituent sublayers in the bilayer are very close to that for the individual films. It was found that a ferromagnetic transition in the La₀.₇Sr₀.₃MnO₃ sublayer significantly modifies the magnetotransport properties of the Pr₀.₅Ca₀.₅MnO₃ constituent sublayer, owing to occurrence of a magnetic proximity effect. The main evidences for this effect are an appearance of the exchange bias interaction between the constituent sublayers; a localizedto-itinerant crossover in the system of polarized electrons, which results in formation of the Griffiths-like ferromagnetic state; and an unusual polaron transport of carriers. The experimental results have been analyzed within the framework of modern theoretical approaches. 2012 Article Magnetic proximity effect in Pr₀.₅Ca₀.₅MnO₃/La₀.₇Sr₀.₃MnO₃ bilayered films / V.G. Prokhorov, G.G. Kaminsky, V.S. Flis, J.M. Kim, T.W. Eom, J.S. Park, Y.P. Lee, V.L. Svetchnikov // Физика низких температур. — 2012. — Т. 38, № 1. — С. 52-61. — Бібліогр.: 44 назв. — рос. 0132-6414 PACS: 71.30.+h, 75.47.Lx, 75.70.–i http://dspace.nbuv.gov.ua/handle/123456789/116770 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. Kaminsky, G.G. Flis, V.S. Kim, J.M. Eom, T.W. Park, J.S. Lee, Y.P. Svetchnikov, V.L. Magnetic proximity effect in Pr₀.₅Ca₀.₅MnO₃/La₀.₇Sr₀.₃MnO₃ bilayered films Физика низких температур |
| description |
The magnetotransport properties of Pr₀.₅Ca₀.₅MnO₃/La₀.₇Sr₀.₃MnO₃ bilayer, and Pr₀.₅Ca₀.₅MnO₃ and
La₀.₇Sr₀.₃MnO₃ films, deposited on LaAlO₃ (001) substrate by pulse laser deposition have been investigated.
The x-ray diffraction and high-resolution electron-microscopy analysis reveals that lattice parameters for the
constituent sublayers in the bilayer are very close to that for the individual films. It was found that a ferromagnetic
transition in the La₀.₇Sr₀.₃MnO₃ sublayer significantly modifies the magnetotransport properties of the
Pr₀.₅Ca₀.₅MnO₃ constituent sublayer, owing to occurrence of a magnetic proximity effect. The main evidences
for this effect are an appearance of the exchange bias interaction between the constituent sublayers; a localizedto-itinerant
crossover in the system of polarized electrons, which results in formation of the Griffiths-like ferromagnetic
state; and an unusual polaron transport of carriers. The experimental results have been analyzed within
the framework of modern theoretical approaches. |
| format |
Article |
| author |
Prokhorov, V.G. Kaminsky, G.G. Flis, V.S. Kim, J.M. Eom, T.W. Park, J.S. Lee, Y.P. Svetchnikov, V.L. |
| author_facet |
Prokhorov, V.G. Kaminsky, G.G. Flis, V.S. Kim, J.M. Eom, T.W. Park, J.S. Lee, Y.P. Svetchnikov, V.L. |
| author_sort |
Prokhorov, V.G. |
| title |
Magnetic proximity effect in Pr₀.₅Ca₀.₅MnO₃/La₀.₇Sr₀.₃MnO₃ bilayered films |
| title_short |
Magnetic proximity effect in Pr₀.₅Ca₀.₅MnO₃/La₀.₇Sr₀.₃MnO₃ bilayered films |
| title_full |
Magnetic proximity effect in Pr₀.₅Ca₀.₅MnO₃/La₀.₇Sr₀.₃MnO₃ bilayered films |
| title_fullStr |
Magnetic proximity effect in Pr₀.₅Ca₀.₅MnO₃/La₀.₇Sr₀.₃MnO₃ bilayered films |
| title_full_unstemmed |
Magnetic proximity effect in Pr₀.₅Ca₀.₅MnO₃/La₀.₇Sr₀.₃MnO₃ bilayered films |
| title_sort |
magnetic proximity effect in pr₀.₅ca₀.₅mno₃/la₀.₇sr₀.₃mno₃ bilayered films |
| publisher |
Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України |
| publishDate |
2012 |
| topic_facet |
Низкотемпеpатуpный магнетизм |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/116770 |
| citation_txt |
Magnetic proximity effect in
Pr₀.₅Ca₀.₅MnO₃/La₀.₇Sr₀.₃MnO₃ bilayered films / V.G. Prokhorov, G.G. Kaminsky, V.S. Flis, J.M. Kim, T.W. Eom, J.S. Park, Y.P. Lee, V.L. Svetchnikov // Физика низких температур. — 2012. — Т. 38, № 1. — С. 52-61. — Бібліогр.: 44 назв. — рос. |
| series |
Физика низких температур |
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2025-07-08T11:01:12Z |
| last_indexed |
2025-07-08T11:01:12Z |
| _version_ |
1837076288134709248 |
| fulltext |
© V.G. Prokhorov, G.G. Kaminsky, V.S. Flis, J.M. Kim, T.W. Eom, J.S. Park, Y.P. Lee, and V.L. Svetchnikov, 2012
Low Temperature Physics/Fizika Nizkikh Temperatur, 2012, v. 38, No. 1, p. 52–61
Magnetic proximity effect in
Pr0.5Ca0.5MnO3/La0.7Sr0.3MnO3 bilayered films
V.G. Prokhorov, G.G. Kaminsky, and V.S. Flis
Institute of Metal Physics of National Academy of Sciences of Ukraine, Kiev 03142, Ukraine
E-mail: pvg@imp.kiev.ua
J.M. Kim, T.W. Eom, 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 January 27, 2011, revised April 18, 2011
The magnetotransport properties of Pr0.5Ca0.5MnO3/La0.7Sr0.3MnO3 bilayer, and Pr0.5Ca0.5MnO3 and
La0.7Sr0.3MnO3 films, deposited on LaAlO 3 (001) substrate by pulse laser deposition have been investigated.
The x-ray diffraction and high-resolution electron-microscopy analysis reveals that lattice parameters for the
constituent sublayers in the bilayer are very close to that for the individual films. It was found that a ferromag-
netic transition in the La0.7Sr0.3MnO3 sublayer significantly modifies the magnetotransport properties of the
Pr0.5Ca0.5MnO3 constituent sublayer, owing to occurrence of a magnetic proximity effect. The main evidences
for this effect are an appearance of the exchange bias interaction between the constituent sublayers; a localized-
to-itinerant crossover in the system of polarized electrons, which results in formation of the Griffiths-like ferro-
magnetic state; and an unusual polaron transport of carriers. The experimental results have been analyzed within
the framework of modern theoretical approaches.
PACS: 71.30.+h Metal-insulator transitions and other electronic transitions;
75.47.Lx Magnetic oxides;
75.70.–i Magnetic properties of thin films, surfaces, and interfaces.
Keywords: magnetotransport properties, ferromagnetic transition, magnetic proximity effect.
1. Introduction
The combination of ferromagnetic (FM) and antiferro-
magnetic (AFM) layers have attracted considerable atten-
tion due to their interesting fundamental science and poten-
tial for applications as magnetic metamaterials with desired
magnetic properties. On the other hand, the development
of hybrid devices based on multilayered films needs de-
tailed information on the mutual influence between consti-
tuent layers. This influence is generally referred to as a
magnetic proximity effect [1], similar to a well-known
proximity effect, which is typical for superconductors. One
of a principal effect provided by the magnetic coupling
between the FM and the AFM layers is manifested by a
shift of the hysteresis loop along the field axis of a ferro-
magnet, and is termed as the exchange bias interaction
[2,3]. At the same time the mutual influence between adja-
cent FM/AFM layers can significantly modify a thermody-
namic behavior of these objects in the wide temperature
range [4]. Furthermore, a magnetic proximity effect can
occur due to the interaction between two magnetic layers
with different FM spin-ordering temperatures ( ).CT The
layer with the higher ordering temperature induces magnet-
ic order into the layer with the lower ordering temperature
at temperatures at which the latter would be paramagnetic.
Similar effects were observed in bilayered and multi-
layered manganite films which manifest not only a signifi-
cant enhancement of the ferromagnetic ordering in the
low-TC layers, but show the anisotropy of saturation mag-
netization and the alternating shape of the temperature-
dependent anisotropic magnetoresistance near the metal–
insulator transition [5–9]. In spite of that a magnetic prox-
imity effect have already been studied for a long time, the
physical nature is still poorly understood.
Magnetic proximity effect in Pr0.5Ca0.5MnO3/La0.7Sr0.3MnO3 bilayered films
Low Temperature Physics/Fizika Nizkikh Temperatur, 2012, v. 38, No. 1 53
In this paper, we report the experimental results for the
Pr0.5Ca0.5MnO3/La0.7Sr0.3MnO3 bilayer (BL) and the pure
Pr0.5Ca0.5MnO3 (PCMO) film, emphasizing a significant
modification in magnetic behavior for the PCMO sublayer,
stimulated by a magnetic proximity effect.
2. Experimental techniques
A cross-beam laser-ablation technique was employed for
the preparation of the films [10]. We used two Nd-YAG
lasers with a wavelength of 1064 nm, a pulse duration of
7.8–10.5 ns, a pulse-repetition rate of 20 Hz, and an energy
of 0.3 J/pulse. The power density of laser beam focused on
the target was 9.5⋅108–2⋅1010 W/cm2. The targets were
manufactured from the PCMO and LSMO powders of the
stoichiometric composition 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 cool-
ing. All films were deposited on a LaAlO3 (001) single
crystal (LAO) with a thickness of 300 nm at the sub-
strate temperature of 770 °C. The thickness of sublayers in
BL was 150 nm with PCMO at the top. Only the as-
deposited films were used for measurements.
The θ–2θ x-ray diffraction (XRD) patterns were ob-
tained using a Rigaku diffractometer with Cu Kα radia-
tion. The lattice parameters evaluated directly from the
XRD data were plotted against 2cos / sin .θ θ With an
extrapolated straight line to 2cos / sin 0,θ θ = a more pre-
cise lattice parameter was obtained. The high-resolution
electron-microscopy (HREM) studies were carried out by
using a Philips CM300UT-FEG microscope with a field
emission gun operated at 300 kV. The point resolution of the
microscope was in the order 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. The microstructure analysis was carried
out at room temperature. The in-plane field-cooled (FC) and
zero-field-cooled (ZFC) magnetization curves were per-
formed by using a Quantum Design SQUID magnetometer.
To avoid an influence of the parasitic (manly diamagnetic)
response from LAO, the magnetization curves obtained for
the bare substrates were extracted from the raw experimen-
tal curves. The resistance measurements were performed
by using the four-probe method in a temperature range of
10–300 K and in a magnetic field up to 5 T.
3. Microstructure
Figure 1 shows the cross-sectional HREM image for BL
which manifests the well-defined sharp interface between
sublayers. Inset (a) presents the θ–2θ XRD scans for
PCMO, LSMO and BL. High intensities of the (002) peaks
manifest that the deposition results in highly c-oriented
films. The Bragg peak for BL displays a double-peak pecu-
liarity, which can be considered as a presence of two crystal-
line phases, belonging to the LSMO and PCMO sublayers,
and can be fitted by two Lorenz functions (dashed lines).
Analysis of the XRD data reveals that the out-of-plane
lattice parameter is c 0.384 and 0.389 nm for PCMO
and LSMO, respectively, while c 0.3867 and 0.3874 nm
for the corresponding sublayers in BL. Inset (b) displays
the fast Fourier transform (FFT) of the high-magnification
cross-sectional HREM image for the BL region, including
the interface between sublayers. The slight splitting of fun-
damental Bragg spots (indicated by white arrows) confirms
a difference of crystal lattice for the constituent sublayers
that is coincident with the XRD data. Analyzing the inters-
pot spacings on the FFT patterns and the HREM images
the following lattice parameters (for pseudocubic symme-
try) were obtained: =a b 0.3841 and 0.386 nm; /c a
1.0076 and 1.0078 for PCMO and LSMO, respectively,
while =a b 0.3842 and 0.3861 nm; /c a 1.0065 and
1.0068 for the corresponding sublayers in BL. Here a
and b are the in-plane lattice parameters. It is clear that
the cross-sectional HREM analysis can not distinguish
difference between a and .b In spite of that the obtained
results are well coincident with those for the bulk com-
pounds [11,12].
Therefore, the lattice parameters for the constituent sub-
layers in BL are very close to that for the individual films.
Moreover, the tetragonal ratio, / ,c a which defines a lat-
tice distortion, provided by a lattice strain, is also almost
the same for the individual films and the BL’s sublayers.
4. Experimental results
Figure 2 displays the temperature dependences of the
in-plane FC and ZFC magnetic moment, ( ),M T for the
PCMO film measured at different applied magnetic fields,
.H The experimental curves testify that the film undergoes
two magnetic transitions with a decreasing temperature.
There are a broad and smooth magnetic transition at
,C NT 150 K, which is typical for this compound [13],
and the next one at *T 50 K, which is manifested by a
Fig. 1. Low-magnification cross-sectional HREM image for the
PCMO/LSMO bilayer. The (002) Bragg peaks for the PCMO and
LSMO film, and the PCMO/LSMO bilayer (a). The FFT pattern
for the PCMO/LSMO interface (b).
100 nm
LAO
PCMO
LSMO
c �
0
2
4
6
2 , deg�
(002)
LSMO PCMO
BL
aIn
te
n
si
ty
,
1
0
cp
s
3
46.0 46.5 47.0 47.5
b
L
A
O
V.G. Prokhorov, G.G. Kaminsky, V.S. Flis, J.M. Kim, T.W. Eom, J.S. Park, Y.P. Lee, and V.L. Svetchnikov
54 Low Temperature Physics/Fizika Nizkikh Temperatur, 2012, v. 38, No. 1
splitting of FC/ZFC ( ),M T curves. First of them, accord-
ing to the magnetic phase diagram [13], is connected with
a transition from the paramagnetic (PM) to the AFM (or
mixed AFM/FM) phase with the decreasing temperature.
More exactly the ,C NT value can be determined from the
temperature dependence of the inverse dc susceptibility,
1( ),T−χ represented by the inset, at a point where the
1( )T−χ curve starts to be deviated from the Curie–Weiss
linear behavior (straight line), which is typical for a para-
magnet. Here 0= /M Hχ μ is a dimensionless value,
where –7
0 = 4 10μ π⋅ H/m is a permeability. Second mag-
netic transition is very often observed in the manganite
compounds and is interpreted as an appearance of the spin-
glass-like (or cluster-glass) state originated from a phase-
separation effect [13,14].
Figure 3 presents the in-plane hysteresis loops, ( ),M H
for the PCMO film taken at different temperatures. The
( )M H dependence at 10 K (curve 1, solid symbols) can
be treated as a superposition of the AFM (linear term) and
the FM [hysteresis term, represented by the inset (a)] con-
tributions. The linear extrapolation of a high-field ( )M H
behavior to H = 0 (indicated by straight lines) allows us
to obtain a saturation magnetic moment for the FM phase
which turn out to be FM
sM 1.0 / MnBμ at 10 K. There
are a coercive field cH ± 320 Oe and a remanent
magnetic moment rM ± 0.12 /Bμ Mn. Therefore, the
magnetic transition at ,C NT 150 K can be treated as a
multiphase transformation with a formation of the AFM
and FM phases simultaneously. Inset (b) shows that the
hysteresis behavior of the magnetization loop, typical for
the FM phase, still persists at =T 200 K, where the film
should be in the PM state. At this temperature ( =T
,200 K )C NT= > the following magnetic characteristics
were obtained: FM
sM 0.015 /Bμ Mn, cH ± 100 Oe
and rM ± 0.0022 /Bμ Mn.
Figure 4 displays the temperature dependences of the in-
plane FC and ZFC magnetic moment, M (T ), for BL
measured at different applied magnetic fields. For compari-
son the inset shows the same dependences for the LSMO
film. It is seen that BL undergoes three magnetic transitions
with the decreasing temperature. First of them occurs at
CT 325 K and manifests the PM→ FM transition in the
LSMO sublayer. It is confirmed by the same value of the
Curie temperature observed for the LSMO individual film
(see inset). Second one at ,C NT belongs to the PCMO sub-
layer and is connected with a composite AFM/FM transi-
tion. Similar to the PCMO individual film, BL demonstrates
a well-defined ZFC/FC ( )M T splitting at low temperature.
Because this phenomenon does not observe for the LSMO
individual film (see inset), one can conclude that the mag-
netic transition at *T belongs to the PCMO sublayer only.
Fig. 2. Temperature dependences of the in-plane FC (solid sym-
bols) and ZFC (open symbols) magnetic moment for the PCMO
film measured at H, T: 0.01 (1), 0.1 (2), 0.5 (3), and 1 (4). The
inset presents the temperature dependences of the inverse dc sus-
ceptibility for the same film. The solid line is the linear fit within
the Curie–Weiss model.
0.5
1.0
1.5
2.0
2.5
20
40
M
ag
n
et
ic
m
o
m
en
t,
/M
n
�
B
2
3
4
PCMO
(Film)
�
–
1
T
C N,
C
W
lin
e
– 1.0 T
– 0.1 T
– 0.01 T
1
T
C N,
100 200
T, K
50 100 150 200 250
T, K
T�
Fig. 3. The in-plane hysteresis loops for the PCMO film meas-
ured at T, K: 10 (1) and 200 (2). Straight lines are the linear
extrapolation of the AFM term. The insets shows the same curves
in detail. Lines are a guide to the eyes.
–2
–1
0
1
2
–5
0
5
–2
–1
0
1
2
1
2
M
S
FM
(Film)
10 K
a
200 K
b
M
ag
n
et
ic
m
o
m
en
t,
/M
n
�
B
M
,
1
0
/M
n
–
3
�
B
M
,
1
0
/M
n
–
2
�
B
PCMO
–400 0 400
–200 0 200
H, Oe
H, Oe
–1.5 –1.0 –50 0 0.5 1.0 1.5
Magnetic field, T
Magnetic proximity effect in Pr0.5Ca0.5MnO3/La0.7Sr0.3MnO3 bilayered films
Low Temperature Physics/Fizika Nizkikh Temperatur, 2012, v. 38, No. 1 55
Figure 5 presents the in-plane hysteresis loops, ( ),M H
for BL taken at different temperatures. Similar to the
PCMO film the ( )M H dependence at 10 K (curve 1, solid
symbols) also can be treated as a superposition of the AFM
(linear term) and the FM (hysteresis term with the satura-
tion magnetic moment) contributions. Analysis of the
( )M H behavior reveals that FM
sM 2.1 /Bμ Mn,
cH ± 180 Oe and rM ± 0.45 /Bμ Mn for BL at
10 K. At the same time the ( )M H curve at 200 K de-
monstrates behavior typical for a FM phase with the satu-
ration magnetic moment of FM
sM 0.565 /Bμ Mn and
the ( )M H hysteresis of cH ± 54 Oe and rM ±
± 0.154 /Bμ Mn. Analysis of the corresponding hystere-
sis loops for LSMO, represented by the inset (b), reveals
that FM
sM 3.43 and 1.15 /Bμ Mn, cH ± 165 and
53 Oe, rM ± 0.7 and 0.197 /Bμ Mn at =T 10 and
200 K, respectively. At 10 K a saturation magnetic mo-
ment of the FM phase for BL is almost equal to a half-sum
of the corresponding magnitudes for the PCMO and
LSMO individual films: FM
sM (BL) [ FM
sM (PCMO) +
FM
sM+ (LSMO)]/2. Such summation is correct because
thickness of the individual sublayers in BL is twice smaller
than that for the individual films. At the same time
(BL)FM
sM FM
sM (LSMO)/2 at 200 K, manifesting that
a major part of the FM phase belongs to the LSMO sublay-
er while the basic state for the PCMO sublayer is close
to PM. For comparison the inset (a) displays the experi-
mental hysteresis loop for the PCMO film (solid symbols)
and the PCMO sublayer (open symbols), which was ex-
tracted from the total ( )M H curve for BL by a following
procedure: extr ( ) = 2 [ ( ) ( ) / 2],PCMO BL LSMOM H M H M H× −
where ( )BLM H and ( )LSMOM H are the experimental
( )M H curves for BL and LSMO, respectively, at 10 K.
It is seen that both dependencies are almost exactly coinci-
dent and have the same ,FM
sM cH and rM values.
Therefore, one can conclude that the shape of hysteresis
loop for BL is controlled mainly by a magnetic behavior of
the constituent sublayers and can be constructed by a direct
summation of the ( )M H curves for the individual films.
It is worth noting that the considered hysteresis loops were
measured after cooling without an applied magnetic field
(ZFC regime).
Figure 6 presents the in-plane hysteresis loops, ( ),M H
for BL taken at 10 K, which were measured after cooling
without (solid symbols) and with (open symbols) an ap-
plied magnetic field of 0.5 T. Insets show that the hystere-
sis loop of BL after cooling with an applied magnetic
Fig. 4. Temperature dependences of the in-plane FC (solid sym-
bols) and ZFC (open symbols) magnetic moment for the
PCMO/LSMO bilayer measured at H, T: 0.01 (1), 0.1 (2), 0.5 (3),
and 1 (4). The inset presents the same dependences for the LSMO
film. Lines are a guide to the eyes.
1
2 1
2
3
1
2
3
4
T�
T
C N,
2
3
4
T
C
LSMO
(Film)
T
C
1
M
ag
n
et
ic
m
o
m
en
t,
/M
n
�
B
100 200
T, K
100 200 300
T, K
300
M
,
/M
n
�
B
BL
Fig. 5. The in-plane hysteresis loops for the PCMO/LSMO bilay-
er measured at T, K: 10 (1) and 200 (2). Lines are a guide to the
eyes. Straight lines are the linear extrapolation of the AFM term.
The inset (a) presents the hysteresis loop for the PCMO film (sol-
id symbols) and the PCMO sublayer (open symbols), extracted
from the total ( )M T for the PCMO/LSMO bilayer (see text).
The inset (b) shows the hysteresis loops for the LSMO film taken
at T, K: 10 (1) and 200 K (2).
–3
–2
–1
0
1
2
3
–1 0 1
–2
0
2
–1 0 1
–2
0
2
a
2
M
S
10 K
LSMO
(Film)
1
2
b
M
S
FM
1
BL
M
ag
n
et
ic
m
o
m
en
t,
/M
n
�
B
M
,
/M
n
�
B
H, T
H, T
–1.5 –1.0 –50 0 0.5 1.0 1.5
Magnetic field, T
M
,
/M
n
�
B
FM
V.G. Prokhorov, G.G. Kaminsky, V.S. Flis, J.M. Kim, T.W. Eom, J.S. Park, Y.P. Lee, and V.L. Svetchnikov
56 Low Temperature Physics/Fizika Nizkikh Temperatur, 2012, v. 38, No. 1
field (FC regime) becomes asymmetric: 338cH − and
+ 224 Oe [see inset (b)]. A shift of the hysteresis loop
along the field axis is observed, as a rule, for the FM/AFM
magnetically coupled system and is called the “exchange
bias” (EB) interaction. The EB, resulting from the ex-
change anisotropy at the FM/AFM interface, is provided
by the coupling between the FM layer and the uncompen-
sated interfacial spins in the AFM layer, the number of
which determines the magnitude of exchange field ( )EBH
[2,3]. This effect is observed upon cooling the FM/AFM
bilayer in the presence of a static magnetic field from a
temperature above the Néel point but below the Curie one
down to a certain temperature < .NT T In our case the FM
LSMO sublayer has CT 325 K while the AFM/FM
PCMO one has NT 150 K. Therefore, cooling down BL
upon an applied magnetic field from a room temperature
up to 10 K, we realize a necessary condition for an appear-
ance of the EB interaction. Moreover, the average coercive
field, cH 281 Oe, becomes larger after cooling in the
FC regime, than that for the ZFC one, cH ± 180 Oe
(see inset (a)) that also is typical for the EB effect [2,3].
Figure 7 is the temperature-dependent resistance, ( ),R T
for PCMO (1) and BL (2) without (solid symbols) and with
(open symbols) an applied magnetic field of 5 T. The mag-
netic field and the transport current were parallel to the film
surface. Because PCMO is a top sublayer of BL, which re-
mains insulating at all temperatures, and the electrical con-
tacts are placed onto its surface, one can conclude that the
obtained ( )R T dependence belongs to the PCMO sublayer
only. In other words, the parallel-resistor circuit (with the
low-resistance FM LSMO sublayer as a shunt) can not be
realized in this case. Both PCMO (1) and BL (2) demon-
strate close to exponential rise of resistance with the de-
creasing temperature without the metal–insulator (MI) tran-
sition in the whole temperature interval. On the other hand, a
more detail analysis reveals a significant difference in the
( )R T behavior for the PCMO film and the PCMO sublayer.
Inset (a) displays the 1ln( / ) vsR T T −− − plot for the same
samples which exhibits a straight-line-like dependence for
PCMO while a nonlinear behavior in the whole temperature
interval for the PCMO sublayer. Moreover, any peculiari-
ties, connected with a formation of the CO state (as a sharp
Fig. 6. The in-plane hysteresis loops for the PCMO/LSMO bilay-
er at T = 10 K measured after the cooling without (ZFC regime,
solid symbols) and with (FC regime, open symbols) an applied
magnetic field of 0.5 T. The insets (a) and (b) present the same
curves in detail. Lines are a guide to the eyes. The asymmetric
shape of the hysteresis loop, represented by the inset (b) testifies
an appearance of the exchange bias interaction.
–3
–2
–1
0
1
2
3
–4 –2 0 2
–5
0
5
–2 0 2
–5
0
5
ZFC
FC
10 K
(1
0
b
FC
H
C
, 10 TH
–2
a
H
C
ZFC
H, 10 T
–2
M
ag
n
et
ic
m
o
m
en
t,
/M
n
�
B
–1.5 –1.0 –50 0 0.5 1.0 1.5
Magnetic field, T
M
,
1
0
/M
n
–
1
�
B
M
,
1
0
/M
n
–
1
�
B
BL
Fig. 7. Temperature dependences of the resistance for the PCMO
film (1) and the PCMO/LSMO bilayer (2) measured without (sol-
id symbols) and with (open symbols) an applied magnetic field of
5 T. Lines are a guide to the eyes. The inset (a) presents the
1ln( / ) vsR T T −− − plot for the same samples without an applied
magnetic field. Lines are a guide to the eyes. The inset (b) dis-
plays the temperature-dependent MR ratio for the same samples.
The solid lines are the theoretical curves obtained within the
framework of the magnetic polaron model.
100 200
10
0
10
1
10
2
10
3
10
4
0.004 0.008
2
4
6
8
100 200
10
1
10
2
3
R
es
is
ta
n
ce
,
�
1
2
ln
(
/
)
R
T
1
2
a
, KT
M
R
,
%
1
2
b
, KT
–1 –1
10
, KT
Magnetic proximity effect in Pr0.5Ca0.5MnO3/La0.7Sr0.3MnO3 bilayered films
Low Temperature Physics/Fizika Nizkikh Temperatur, 2012, v. 38, No. 1 57
change in the slope of these curves, for example), did not
found. It can be explained by influence of the lattice strain
which leads to suppression of the CO ordering, because
the as-deposited films were used for these measurements
[10–18], or to significant increase of the CO temperature
higher than a room one [19]. Inset (b) shows that the magne-
toresistance (MR) value is higher for the PCMO sublayer
than that for the PCMO film at all temperatures. Here MR is
defined by 100% [ (0) ( )] / ( ),R R H R H× − where (0)R and
( )R H are the resistances without and with an applied mag-
netic field of 5 T.
5. Discussion
Let us analyze the obtained results in terms of a magnetic
proximity effect or a magnetic coupling between the consti-
tuent layers in BL. As is evident from the foregoing the hys-
teresis loops are almost the same for the PCMO individual
film and the PCMO sublayer, grown on LSMO, (see inset
(a) in Fig. 5) that testify a very insignificant mutual influ-
ence between the BL’s sublayers. However, the cooling of
BL under an applied magnetic field (FC regime) leads to an
appearance of the EB interaction, which is manifested by a
shift of the hysteresis loop along a magnetic field axis. This
phenomenon can be treated as an evidence for a magnetic
proximity effect in the PCMO/LSMO bilayer.
Now we will consider the magnetic influence of the
FM LSMO sublayer on the thermodynamic characteris-
tics of the PCMO one, such as the ( )M T dependencies
taken at different magnetic fields. Similar to a hysteresis
loop (see Fig. 5) the ( )M T curves for the PCMO sublay-
er were extracted from the total ( )M T dependencies for
BL: extr ( ) = 2 [ ( ) ( ) / 2],PCMO BL LSMOM T M T M T× − where
( )BLM T and ( )LSMOM T are the experimental ( )M T
curves for BL and LSMO, respectively.
Figure 8 presents the in-plane ZFC (open symbols) and
FC (solid symbols) ( )M T dependences for the PMCO
sublayer (square symbols) measured at different magnetic
field. For comparison the same dependences for the PCMO
individual film (circle symbols) are shown as well. It is
seen that the PCMO sublayer manifests the ( )M T beha-
vior at =H 0.01 T, which is typical for the FM phase with
the Curie point close to that for the LSMO sublayer. At the
same time the FM state is drastically suppressed with the
increasing external magnetic field and becomes almost
undistinguished at =H 1 T. In the last case the ( )M T
curves for the PCMO film and the PCMO sublayer are
almost coincident. More clearly it can be observed on the
temperature dependences of the inverse dc susceptibility,
represented by Fig. 9. Inset shows that 1( )T−χ depen-
dence, taken at =H 0.01 T, excellently described by the
Bloch law 3/2( ) ,CT T −−∼ with =CT 330 K (solid line),
which is typical for common FMs [20]. On the other hand,
1( ) ( )T T−χ − θ∼ at =H 1 T (straight line, curve 3), ma-
nifesting the occurrence of the PM state, where θ is a cha-
racteristic temperature. A frustration of the long-range spin
ordering by an applied magnetic field (that is not typical
for common FMs) allow us to suggest that the observed
FM state has a fluctuation origin. The long-term spin-
ordered fluctuations can appear in the PM matrix, leading
to the formation of the Griffiths phase [21] above the
FM transition point ( ,> C NT T 150 K). Moreover, at
0H → these fluctuations can coalesce and result in the
formation of the large-size FM clusters [22], which are
observed in our case at =H 0.01 T (see Figs. 8, 9). Ac-
cording to theoretical prediction the Griffiths phase is sup-
pressed by an applied magnetic field that also correlates
with our results. The observed broad peak on the ZFC and
FC ( )M T curves for the PCMO sublayer near ,C NT at
=H 0.1 T testifies that the Griffiths-like fluctuations be-
come more stable in a region of the magnetic phase transi-
tion, that is typical for such type of the formations. It is
explained by an unlimited rise of the correlation length at a
Fig. 8. Temperature dependences of the in-plane FC (solid sym-
bols) and the ZFC (open symbols) magnetic moment for the
PCMO film (circle symbols) and the PCMO sublayer (square
symbols) taken at a different applied magnetic field.
0
0.1
0
0.2
0.4
1
2
H = 0.01 T
T
C
H = 0.1 T
T
C N,
PCMO (Film);
PCMO (Layer)
H = 1 T
T
C N,
100 200
, KT
M
ag
n
et
ic
m
o
m
en
t,
/M
n
�
B
T�
T�
V.G. Prokhorov, G.G. Kaminsky, V.S. Flis, J.M. Kim, T.W. Eom, J.S. Park, Y.P. Lee, and V.L. Svetchnikov
58 Low Temperature Physics/Fizika Nizkikh Temperatur, 2012, v. 38, No. 1
critical point of the magnetic transition. Consequently, one
can conclude that the FM LSMO sublayer induces a mag-
netic order into the PCMO sublayer, which is resulted in an
appearance of the Griffiths-like state at temperature at
which the PCMO sublayer would be paramagnetic.
The inset in Fig. 2 and Fig. 9 exhibit the linear 1( )T−χ
behavior at ,C NT T≥ for the PCMO film and the PCMO
sublayer, respectively. In the latter case it is true at high
magnetic field only. Such type of dependence is typical for
the PM materials [23] and can be expressed by the Curie–
Weiss (CW)-type law: 1( ) ( ) / ,CWT T C−χ + θ∼ where
2
eff= / 3CW BC N kμ is the CW constant, which can be
obtained from the experimental curve, effμ is the atom's
effective magnetic moment, and N is the number of atoms
per unit cell. Analysis reveals that effective magnetic mo-
ment, obtained from the experimental data, effμ 13.3
and 17.8 Bμ for the PCMO film and the PCMO sublayer,
respectively, is larger than that is predicted by the CW-
theory for a classical PM, theor
effμ 4.42 Bμ /Mn. The fol-
lowing expression was used for its estimation:
theor
eff 1 1 2 2= ( 1) (1 ) ( 1),g xS S x S Sμ + + − +
where, =g 2 is the Landé factor, x is the Ca concentration,
and 1 =S 3/2 and 2 =S 2 are the spin values of Mn4+ and
Mn+3 ions, respectively. A similar PM response with the
enhanced magnetic moment has already been observed in
the manganites [24] and was attributed to an existence of the
magnetic small-size polarons, which are typical for the di-
luted magnetic semiconductors. In this case the expression
for the effective magnetic moment can be modified:
theor
eff =μ
1 2 1 2 2 2= ( )( 1) (1 ) ( 1),g x S S P S S P x Px S S+ + + + − − +
where 0 6P≤ ≤ is a number of the polarized electrons
[25]. The carried out calculations reveal that P 4.2 and
5.8 for the PCMO film and the PCMO sublayer, respec-
tively, which are well coincident with the theoretical pre-
diction [25]. Taking into account the experimental effμ
values and assuming a spherical shape of the magnetic
polarons with a volume of 3 /Dπ 6, we estimate their aver-
age diameter to be D 0.75 and 0.79 nm for the PCMO
film and the PCMO sublayer, respectively. It is worth not-
ing that the magnetic polaron clusters of the similar size
origin have already observed in the PCMO compound by a
neutron scattering [26], a magnetic measurement [27], and
an electron-microscopy study [28]. Therefore, the FM
LSMO sublayer introduces the magnetic order into the
PCMO sublayer and gives an impetus to a topological
magnetic transformation from the small-size magnetic-
polaron-PM state to the Griffiths-like phase with the large-
size fluctuated FM clusters. In other words it is the loca-
lized-to-itinerant crossover in the system of electrons [14].
Let us consider the transport properties of the PCMO
film and the PCMO sublayer, taking into account the pres-
ence of the magnetic polarons. Inset (a) in Fig. 7 manifests
that the 1ln( / ) vsR T T −− − dependence is linear for the
PCMO film while significantly deviated from that for the
PCMO sublayer. Traditionally, the thermally-activated pola-
ronic transport of carriers in the manganites expressed by
0( , ) = exp( / )a BR T H R T E k T [29]. Here 0R is the con-
stant, which is inversely proportional to the polaron hopping
frequency, aE is the activation energy, and Bk is the
Boltzmann constant. However, the interaction between the
auto-localized electron and the surrounding spins leads to a
modification of the activation energy [30,31]. In this case
the activation energy has to change in the presence of a spin-
ordered coating, 0= (1 cos ),a a ijE E − 〈 θ 〉 where 0
aE is the
field-independent activation energy and ijθ is the angle
between the i and j ion spins. Taking into account, that for
the uncorrelated spins 2 2cos = cos = ( / ) ,ij i sM M〈 θ 〉 θ
one can to write 0 2= [1 ( / ) ],a a sE E M M− where sM is
a saturation magnetic moment. For convenience will
be used an expression for the temperature-dependent mag-
netic moment of the magnetic polaron ( , ) =M T H
eff= (0, )exp( / ),BM H k T H− μ where (0, )M H is the
Fig. 9. Temperature dependences of the inverse dc susceptibility
χ–1 for the PCMO sublayer measured at H, T: 0.01 (1), 0.1 (2),
and 1 (3). The solid lines are the linear fit within the Curie–Weiss
model. The inset shows the same curve at H = 0.01 T. The solid
line is the Bloch's curve for the FM state.
10
20
30
2
4
�
–
1
1
2
3
(Layer)
, KT
�
–
1
( – )� T T
C
–3/2
�
–1
H = 0.01 T
PCMO
100 200 300
�
–1
C
W
lin
e
T
C N,
50 100 150 200 250
, KT
Magnetic proximity effect in Pr0.5Ca0.5MnO3/La0.7Sr0.3MnO3 bilayered films
Low Temperature Physics/Fizika Nizkikh Temperatur, 2012, v. 38, No. 1 59
magnetic moment at = 0T and effμ is the effective mag-
netic moment of magnetic polaron cluster [32]. Therefore,
the ( , )R T H dependence for a magnetic polaron can be
written as
( )20
eff
0
1 exp /
( , ) = exp .
a B
B
E k T H
R T H R T
k T
⎧ ⎫⎡ ⎤− − μ⎢ ⎥⎪ ⎪⎣ ⎦
⎨ ⎬
⎪ ⎪
⎩ ⎭
(1)
The experimental 1ln( / ) vsR T T −− − curves for
the PCMO film can be excellently described by the pre-
sented expression (solid lines) with the fitting parameters of
0
aE 1500 K ( = 0),H and 0
aE 1500 K and effμ 20
Bμ (H = 5 T) (see Fig. 10,a). In contrast to that the PCMO
sublayer manifests the nonlinear 1ln( / ) vsR T T −− − be-
havior even though an applied magnetic field is absent. It
can be explained by the following reasons. First, the inter-
nal magnetic field in BL can be originated from the spon-
taneous magnetization of the LSMO sublayer, which has
Curie point CT 325 K. Analysis of the magnetic prop-
erties for BL (a remanent magnetic moment, for example)
reveals that the FM transition in the LSMO sublayer re-
sults in the occurring magnetic field of about 0.01 T onto
its surface. It is coincident with the published data on a
spontaneous magnetization for the single-crystalline
La0.7(Sr,Ca)0.3MnO3 film [33]. Second, the analysis of the
( )M T curves for the PCMO sublayer (see Fig. 8) reveals
that due to a magnetic proximity effect the large-size FM
clusters are formed at H → 0. Using = 0.01H and 5 T,
and 0
aE 1500 K, the experimental 1ln( / ) vsR T T −− −
curves for the PCMO sublayer were fitted on the base of
Eq. (1) with effμ as a fitting parameter. Without an ap-
plied magnetic field the better agreement between the ex-
perimental and theoretical curves observed for
eff 20000 Bμ μ while at = 5 TH the effective magnetic
moment becomes significantly smaller, eff 40 .Bμ μ The
obtained results are completely correlated with the magneti-
zation data and testify that the giant FM clusters occur at
0,H → which size is crucial decreased by an applied mag-
netic field. The solid lines shown by the inset (b) in Fig. 7
demonstrate that the MR(T) dependences taken at = 5 TH
also can be excellently described on the base of magnetic
polaron model with the same fitting parameters: 0
aE 1500
K, and eff 20 Bμ μ and 40 Bμ for the PCMO film and
the PCMO sublayer, respectively. Therefore, a magnetic
proximity effect manifests itself in the transport properties of
the PCMO/LSMO bilayer as a nonlinear
1ln( / ) vsR T T −− − dependence without an applied mag-
netic field.
A further peculiarity of the magnetic properties for the
investigated films, manifesting as an additional magnetic
transition at low temperature, is needed in a discussion.
Figures 2 and 4 exhibit that all films exhibit the well-
defined FC/ZFC ( )M T splitting and the non-monotonic
ZFC ( )M T behavior with a peak at certain temperature,
*.T Usually such a phenomenon is interpreted as an occur-
rence of the cluster-glass or spin-glass-like phase, which
can be governed by the microstructure peculiarities (nano-
size column-like texture) [34], the doping of transition
metal ions at the Mn site [35,36], the lattice strains [37], or
the intrinsic phase-separation effect [13]. Two different
approaches are employed for a description of the magnetic
properties for manganites in the phase-separated state.
There are the modified classical spin-glass theory [14,43]
and the model of the superparamagnetic (SPM) clusters
with a strong dipolar interaction [38–42]. Figure 10,b
presents the magnetic-field dependences of *,T which was
evaluated as a peak position on the ZFC ( )M T curve, for
Fig. 10. The 1ln( / ) vsR T T −− − plots for the PCMO film (1)
and the PCMO/LSMO bilayer (2) measured without (solid sym-
bols) and with (open symbols) an applied magnetic field. The
solid lines are the corresponding theoretical curves obtained with-
in the framework of the magnetic polaron model (a). The magnet-
ic-field dependences of *T extracted from the peak in the ZFC
( )M T curve for the PCMO film (1) and the PCMO/LSMO bi-
layer (2). The solid and dashed lines are the theoretical curves
obtained within the framework of the spin-glass-like and the in-
teracting SPMs models, respectively (b).
0.5 1.0
0
2
4
6
8
10
0.2 0.4 0.6 0.8 1.0
20
40
60
ln
(
/
),
K
R
T
�
–
1
�
, PCMO;
, BL
a
2
,
K
T
�
PCMO;
BL
1
2
Magnetic field, T
b
1
T , 10 K
–1 –2 –1
V.G. Prokhorov, G.G. Kaminsky, V.S. Flis, J.M. Kim, T.W. Eom, J.S. Park, Y.P. Lee, and V.L. Svetchnikov
60 Low Temperature Physics/Fizika Nizkikh Temperatur, 2012, v. 38, No. 1
PCMO and BL. It is seen that the *( )T H dependence
for the individual PCMO film can be extrapolated by
the Almeida–Thouless line, predicted for a classical spin-
glass [43,44]:
1/32
* *
2
3( ) = (0) 1 ,
4
HT H T
J
⎡ ⎤⎛ ⎞⎢ ⎥− ⎜ ⎟⎜ ⎟⎢ ⎥⎝ ⎠⎣ ⎦
(2)
where J is the exchange integral. In spite of that the fitted
J value turn out to be a twice smaller than that is esti-
mated in the framework of a mean-field model,
= 3 / [2 ( 1)],B CJ k T zS S + one can consider that the agree-
ment between the theoretical (solid line) and the experi-
mental (circle symbols) curves is quite reasonable. Here
=CT 150 K is the Curie temperature, = 6z is the number
of nearest neighbor atoms (because we consider the cubic
unit cell) and =S 1.75 is the average spin value for the
Mn ion. The observed difference in the J values most
probably connected with an incorrect choice of CT for the
estimation of the exchange integral. In our case the Cutie
point has be define the long-range order between the mag-
netic polarons rather than between the individual atoms.
Larger distance between the nearest magnetic polarons ra-
ther than the Mn ions that can lead to a decrease of the ex-
change interaction. At the same time the *( )T H depen-
dences for the PCMO sublayer more properly described by
an expression, * *( ) = (0) / (1 ),T H T H+β which was ob-
tained in the framework of model for the interacting SPM
clusters [38]. Here β 3 T–1 is a certain coefficient be-
tween the saturation magnetic moment and an applied mag-
netic field. Moreover, the most significant difference be-
tween experimental *( )T H curves for the PCMO film and
the PCMO sublayer observes in a low-field range. As dis-
cussed earlier at 0H → the large-size FM clusters form in
the PCMO sublayer, which are induced by the FM LSMO
sublayer due to a magnetic proximity effect. Therefore, the
small-size magnetic polarons demonstrate the magnetic
properties at low temperature close to the spin-glass-like
system while the large-size FM clusters have magnetic be-
havior typical for the interacting SPM particles.
6. Conclusions
We have performed magnetotransport measurements of
the PCMO/LSMO bilayer deposited on LAO substrate by a
cross-beam laser ablation. For comparison, the PCMO and
LSMO films have also been prepared. The XRD and
HREM analysis reveals that the lattice parameters for the
constituent sublayers in BL are very close to that for the
individual films. Moreover, the tetragonal ratio, / ,c a
which defines a lattice distortion, provided by a lattice
strain, is also almost the same.
It was shown that the FM transition in the LSMO sub-
layer at CT 325 K with the decreasing temperature sig-
nificantly modifies the magnetotransport properties of the
PCMO constituent sublayer, owing to an occurrence of a
magnetic proximity effect.
(i) The cooling of the PCMO/LSMO bilayer under an
applied magnetic field of 0.5 T (FC regime) leads to an
appearance of the exchange bias interaction between the
constituent sublayers, which is manifested by a shift of the
hysteresis loop along a magnetic field axis.
(ii) The FM LSMO sublayer introduces the magnetic
order into the PCMO sublayer and gives an impetus to a
topological magnetic transformation (at 0)H → from the
small-size magnetic-polaron-PM state to the Griffiths-like
phase with the large-size fluctuated FM clusters that can be
treated as a localized-to-itinerant crossover in the system
of polarized electrons. The fluctuated FM state, which is
originated from a magnetic proximity effect, turn out to be
a very sensitive to an applied magnetic field and can be
fully frustrated at =H 1 T.
(iii) A magnetic proximity effect manifests itself in the
polaron transport as a nonlinear 1ln( / ) vsR T T −− − de-
pendence without an applied magnetic field. It is explained
by an appearance of the internal magnetic field originated
from the spontaneous magnetization of the LSMO sublayer
and an existence of the large-size fluctuated FM clusters.
(iiii) At low temperature the PCMO film demonstrate
the magnetic properties close to the spin-glass-like system
while the PCMO sublayer, owing to a magnetic proximity
effect, has magnetic behavior typical for the interacting
SPM particles.
Therefore, the development of hybrid devices based on
multilayered films needs detailed information on the mu-
tual influence between constituent layers, including the
occurrence of a magnetic proximity effect.
This work was supported by the NRF/MEST through
the Quantum Photonic Science Research Center, Korea.
V. Svetchnikov is grateful to the financial support of Neth-
erlands Institute for Metal Research.
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