Influence of structural disorder on magnetic and transport properties of (La₀.₇Sr₀.₃)₀.₅(Pr₀.₆₅Ca₀.₃₅)₀.₅MnO₃ films
Magnetic and transport properties of (La₀.₇Sr₀.₃)₀.₅(Pr₀.₆₅Ca₀.₃₅)₀.₅MnO₃ films prepared by a «co-deposition» utilizing the laser-ablation technique are investigated in a wide temperature range. The film deposited at 300 °C has a nano-crystalline disordered structure and exhibits a paramagnetic...
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Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України
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| Цитувати: | Influence of structural disorder on magnetic and transport properties of (La₀.₇Sr₀.₃)₀.₅(Pr₀.₆₅Ca₀.₃₅)₀.₅MnO₃ films / V.G. Prokhorov, V.S. Flis, G.G. Kaminsky, Y.P. Lee, J.S. Park, V.L. Svetchnikov // Физика низких температур. — 2005. — Т. 31, № 2 — С. 213-221. — Бібліогр.: 35 назв. — англ. |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine| id |
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irk-123456789-1213942017-06-15T03:03:03Z Influence of structural disorder on magnetic and transport properties of (La₀.₇Sr₀.₃)₀.₅(Pr₀.₆₅Ca₀.₃₅)₀.₅MnO₃ films Prokhorov, V.G. Flis, V.S. Kaminsky, G.G. Lee, Y.P. Park, J.S. Svetchnikov, V.L. Низкотемпеpатуpный магнетизм Magnetic and transport properties of (La₀.₇Sr₀.₃)₀.₅(Pr₀.₆₅Ca₀.₃₅)₀.₅MnO₃ films prepared by a «co-deposition» utilizing the laser-ablation technique are investigated in a wide temperature range. The film deposited at 300 °C has a nano-crystalline disordered structure and exhibits a paramagnetic temperature dependence of the magnetization with a narrow peak (ΔT ≃ 10 K) at TG ≃ 45 K, which can be interpreted as a paramagnetic → superparamagnetic transition. A short-term annealing of the as-deposited film at 750 °C leads to the formation of a high-textured polycrystalline microstructure and to the appearance of ferromagnetic (FM) and metal—insulator (MI) transitions at TC ≃ 240 K and TP ≃ 140 K, respectively. The observed discrepancy between TP and TC values can be ascribed to a percolating nature of the MI transition, with an exponent of 5.3 for the percolating conductivity. The film deposited at Tsub ≃ 740 °C is composed of the lattice strain-free and the lattice-strained crystallites with different lattice parameters and TC‘s, and is consistently described in the framework of the Millis model [A.J. Millis, T. Darling, and A. Migliori, J. Appl. Phys. 83, 1588 (1998)]. For a single-phase crystalline film obtain TC ≃ 270 K and TP ≃ 260 K. 2005 Article Influence of structural disorder on magnetic and transport properties of (La₀.₇Sr₀.₃)₀.₅(Pr₀.₆₅Ca₀.₃₅)₀.₅MnO₃ films / V.G. Prokhorov, V.S. Flis, G.G. Kaminsky, Y.P. Lee, J.S. Park, V.L. Svetchnikov // Физика низких температур. — 2005. — Т. 31, № 2 — С. 213-221. — Бібліогр.: 35 назв. — англ. 0132-6414 PACS: 71.30.+h, 75.47.Gk, 75.47.Lx http://dspace.nbuv.gov.ua/handle/123456789/121394 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. Flis, V.S. Kaminsky, G.G. Lee, Y.P. Park, J.S. Svetchnikov, V.L. Influence of structural disorder on magnetic and transport properties of (La₀.₇Sr₀.₃)₀.₅(Pr₀.₆₅Ca₀.₃₅)₀.₅MnO₃ films Физика низких температур |
| description |
Magnetic and transport properties of (La₀.₇Sr₀.₃)₀.₅(Pr₀.₆₅Ca₀.₃₅)₀.₅MnO₃ films prepared by a
«co-deposition» utilizing the laser-ablation technique are investigated in a wide temperature
range. The film deposited at 300 °C has a nano-crystalline disordered structure and exhibits a paramagnetic
temperature dependence of the magnetization with a narrow peak (ΔT ≃ 10 K) at
TG ≃ 45 K, which can be interpreted as a paramagnetic → superparamagnetic transition.
A short-term annealing of the as-deposited film at 750 °C leads to the formation of a high-textured
polycrystalline microstructure and to the appearance of ferromagnetic (FM) and metal—insulator
(MI) transitions at TC ≃ 240 K and TP ≃ 140 K, respectively. The observed discrepancy between
TP and TC values can be ascribed to a percolating nature of the MI transition, with an exponent of
5.3 for the percolating conductivity. The film deposited at Tsub ≃ 740 °C is composed of the lattice
strain-free and the lattice-strained crystallites with different lattice parameters and TC‘s, and is
consistently described in the framework of the Millis model [A.J. Millis, T. Darling, and A. Migliori,
J. Appl. Phys. 83, 1588 (1998)]. For a single-phase crystalline film obtain TC ≃ 270 K and
TP ≃ 260 K. |
| format |
Article |
| author |
Prokhorov, V.G. Flis, V.S. Kaminsky, G.G. Lee, Y.P. Park, J.S. Svetchnikov, V.L. |
| author_facet |
Prokhorov, V.G. Flis, V.S. Kaminsky, G.G. Lee, Y.P. Park, J.S. Svetchnikov, V.L. |
| author_sort |
Prokhorov, V.G. |
| title |
Influence of structural disorder on magnetic and transport properties of (La₀.₇Sr₀.₃)₀.₅(Pr₀.₆₅Ca₀.₃₅)₀.₅MnO₃ films |
| title_short |
Influence of structural disorder on magnetic and transport properties of (La₀.₇Sr₀.₃)₀.₅(Pr₀.₆₅Ca₀.₃₅)₀.₅MnO₃ films |
| title_full |
Influence of structural disorder on magnetic and transport properties of (La₀.₇Sr₀.₃)₀.₅(Pr₀.₆₅Ca₀.₃₅)₀.₅MnO₃ films |
| title_fullStr |
Influence of structural disorder on magnetic and transport properties of (La₀.₇Sr₀.₃)₀.₅(Pr₀.₆₅Ca₀.₃₅)₀.₅MnO₃ films |
| title_full_unstemmed |
Influence of structural disorder on magnetic and transport properties of (La₀.₇Sr₀.₃)₀.₅(Pr₀.₆₅Ca₀.₃₅)₀.₅MnO₃ films |
| title_sort |
influence of structural disorder on magnetic and transport properties of (la₀.₇sr₀.₃)₀.₅(pr₀.₆₅ca₀.₃₅)₀.₅mno₃ films |
| publisher |
Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України |
| publishDate |
2005 |
| topic_facet |
Низкотемпеpатуpный магнетизм |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/121394 |
| citation_txt |
Influence of structural disorder on magnetic and transport properties of (La₀.₇Sr₀.₃)₀.₅(Pr₀.₆₅Ca₀.₃₅)₀.₅MnO₃ films / V.G. Prokhorov, V.S. Flis, G.G. Kaminsky, Y.P. Lee, J.S. Park, V.L. Svetchnikov // Физика низких температур. — 2005. — Т. 31, № 2 — С. 213-221. — Бібліогр.: 35 назв. — англ. |
| series |
Физика низких температур |
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| first_indexed |
2025-07-08T19:49:46Z |
| last_indexed |
2025-07-08T19:49:46Z |
| _version_ |
1837109551329968128 |
| fulltext |
Fizika Nizkikh Temperatur, 2005, v. 31, No. 2, p. 213–221
Influence of structural disorder on magnetic and transport
properties of (La0.7Sr0.3)0.5(Pr0.65Ca0.35)0.5MnO3 films
V.G. Prokhorov, V.S. Flis, and G.G. Kaminsky
Institute of Metal Physics, National Academy of Sciences of Ukraine, Kiev, 03142, Ukraine
E-mail: pvg@imp.kiev.ua
Y.P. Lee and J.S. Park
Quantum Photonic Science Research Center and Department of Physics, Hanyang University
Seoul, 133-791 Korea
V.L. Svetchnikov
National Center of High-Resolution Electron Microscopy
Rotterdamseweg 137, 2628AL, Delft, The Netherlands
Received April 6, 2004, revised June 27, 2004
Magnetic and transport properties of (La Sr Pr Ca MnO07 0 3 0 5 0 65 0 35 0 5 3. . . . . .) ( ) films prepared by a
«co-deposition» utilizing the laser-ablation technique are investigated in a wide temperature
range. The film deposited at 300 �C has a nano-crystalline disordered structure and exhibits a para-
magnetic temperature dependence of the magnetization with a narrow peak (�T � 10 K) at
TG � 45 K, which can be interpreted as a paramagnetic � superparamagnetic transition.
A short-term annealing of the as-deposited film at 750 �C leads to the formation of a high-textured
polycrystalline microstructure and to the appearance of ferromagnetic (FM) and metal—insulator
(MI) transitions at TC � 240 K and TP � 140 K, respectively. The observed discrepancy between
TP and TC values can be ascribed to a percolating nature of the MI transition, with an exponent of
5.3 for the percolating conductivity. The film deposited at Tsub � 740 �C is composed of the lattice
strain-free and the lattice-strained crystallites with different lattice parameters and TC‘s, and is
consistently described in the framework of the Millis model [A.J. Millis, T. Darling, and A. Mig-
liori, J. Appl. Phys. 83, 1588 (1998)]. For a single-phase crystalline film obtain TC � 270 K and
TP � 260 K.
PACS: 71.30.+h, 75.47.Gk, 75.47.Lx
1. Introduction
Half a century ago, Volger [1] found that a bulk
sample of La Sr MnO0 8 02 3. . exhibited a large magne-
toresistance near room temperature. The recent dis-
covery of colossal magnetoresistance (CMR) in thin
films of the general formula R A MnO1 3�x x , where R
is a rare-earth cation and A is alkali or alkaline earth
cation [2,3], initiated numerous investigations not
only because of their interesting fundamental science
but because of possibilities for device applications
[4,5]. Most of the early theoretical works on manga-
nites focused on the relationship between the trans-
port and magnetic properties and explained the coex-
istence of ferromagnetism and metallic behavior
within the framework of the «double exchange» mo-
del, which considered the magnetic coupling between
Mn3�and Mn4� ions, resulting from the motion of an
electron between two partially filled d shells governed
by the strong on-site Hund’s coupling [6–8]. In spite
of considerable scientific efforts, the complex inter-
play of charge, lattice, spin, and orbital degrees of
freedom in these systems is not completely under-
stood. The situation is complicated significantly by
the fact that the magnetic and the transport properties
of the manganites are strongly dependent on the cat-
ion size, lattice strain, and microstructure.
As the CMR effect develops more strongly near the
Curie point (TC), i.e., near the metal—insulator (MI)
transition, which, in turn, reflects the electron—pho-
© V.G. Prokhorov, V.S. Flis, G.G. Kaminsky, Y.P. Lee, J.S. Park, and V.L. Svetchnikov, 2005
non coupling and the antiferromagnetic superex-
change and the FM exchange interactions, an analysis
of the influence of the crystal structures on TC is very
useful. A unified phase diagram as a function of the
electronic transfer integral, which could be deter-
mined mainly by Mn–O bond length and Mn–O–Mn
angle, was presented recently [9]. The final result for
TC can be written approximately in the following form
[10,11]:
T x x W /dC � ( ) cos .1 35� � � Mn–O,
where x is the concentration of a divalent ion, W is
the bandwidth, � is the tilt angle in the plane of the
bond, and dMn–O is the Mn–O bond length. There-
fore, any perturbation in the translation symmetry of
the crystal lattice can lead to the variation of � and
dMn–O and, consequently, results in a change of TC.
One way to control the stress exerted on the crystal
lattice is a replacement of the rare-earth or the alkali
ions by other ions with a different size. It is well
known that Pr Ca MnO065 035 3. . (PCMO), owing to a
small Pr-ion radius, remains an insulator in both
the paramagnetic and FM states [12], while the
La Sr MnO0.7 0.3 3 (LSMO) shows a metallic behavior
of the electrical resistance in the whole temperature
range [13]. It was recently found that the substitution
of the small-size Pr ion by La in Pr Ca MnO067 033 3. .
compound led to the appearance of a MI transition at
low temperature owing to the melting of a charge-or-
dered insulating state [14]. On the other hand, the
substitution of Sr for Ca in Pr Ca Sr MnO07 03 3. . �x x in-
duces the formation of the low-temperature metallic
state, as well [15]. The influence of a lattice strain
(and stress) accumulated during film deposition was
intensively investigated, and it was shown that the
lattice strain played an important role in the forma-
tion of spin- and charge-ordered states [16–19]. How-
ever, the influence of structurally quenched disorder
on the magnetic ordering is still poorly understood.
In this paper we report our experimental results for
(La Sr Pr Ca MnO07 03 05 065 035 05 3. . . . . .) ( ) films prepared
by a «co-deposition» utilizing the laser-ablation tech-
nique from two independent PCMO and LSMO tar-
gets. Several films with different structural order
were prepared to investigate the influence of the dif-
ferent types of crystal disorder on the magnetic and
transport properties of the films.
2. Experimental techniques
A cross-beam laser-ablation technique was employ-
ed for preparation of the films. A detailed description
of the technique was presented elsewhere [20]. The
deposition was carried out simultaneously from both
LSMO and PCMO targets. We used two Nd-YAG la-
sers 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 2� W cm/ .
The targets were prepared 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 deposi-
tion and 600 Torr during cooling. Under these condi-
tions were grown (La Sr Pr Ca MnO07 03 05 065 035 05 3. . . . . .) ( )
films at Tsub = 300 (LPM1) and 740 �C (LPM2).
In addition, the LPM1 and LPM2 films were annealed
at Tann = 750 (LPM1A) and 900 �C (LPM2A) for 1 h
in air, respectively. All the films were deposited on a
LaAlO3 (001) single crystal and have a thickness of
d � 200 nm.
The –2 x-ray diffraction (XRD) patterns were
obtained using a Rigaku diffractometer with CuK
ra-
diation. The lattice parameters evaluated directly
from the XRD data were plotted against cos sin2 / .
With an extrapolated straight line to cos sin2 / = 0,
a more precise 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 of
the order of 0.12 nm. The cross-sectional specimens
were prepared by the standard techniques using me-
chanical polishing followed by ion-beam milling at a
grazing incidence. The microstructure analysis was
carried out at room temperature. The resistance mea-
surements 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) magnetization was
measured using a Quantum Design SQUID magne-
tometer in a temperature range of 4.2–300 K.
3. Experimental results
3.1. Microstructure of the films
Figure 1,a presents the (002) Bragg peaks for the
LPM1 (curve 1) and the LPM1A (curve 2) films. It is
seen that there is no crystalline phase in the LPM1
film and only the Bragg peak of the substrate is ob-
servable. It indicates the formation of an amorphous
or a fine-crystalline disordered microstructure in the
film. The LPM1A film displays only the high-inten-
sity (00l) peaks, demonstrating that a short-term an-
nealing at 750 �C results in a highly c-oriented film with
an out-of-plane lattice parameter of c � 0.3855 nm.
The value obtained for the lattice parameter is in be-
tween that for the bulk LSMO (ac = 0.3876 nm [13])
214 Fizika Nizkikh Temperatur, 2005, v. 31, No. 2
V.G. Prokhorov et al.
and PCMO (ac � 0.3843 nm [21]) compounds with a
cubic symmetry. Figure 1,b displays that the LPM2
film manifests a split (002) Bragg peak (curve 1) and
indicates the presence of two crystalline phases with
c � 0.3961 and 0.3888 nm. An additional annealing
at 900 �C results in a single-phase crystal structure
(curve 2) in the film with c � 0.3873 nm.
More-detailed information about the microstruc-
ture of the films can be obtained from the analysis of
the HREM images. Figure 2 shows the cross-sectional
HREM images for the LPM1 (a) and the LPM1A (b)
films across the interface between film and substrate
(indicated by white dashed lines). The electron-dif-
fraction pattern, displayed in the inset of Fig. 2,a,
demonstrates that the LPM1 film is not completely
amorphous, as it has been recognized by the XRD
data, but consists of a small-size (D � 5.5 nm) disor-
dered crystallites. Figure 2,b shows that annealing of
the LPM1 film leads to the formation of a column-like
high-textured microstructure with grain boundaries
containing edge dislocations and regions of an uncrys-
tallized phase. The inset of Fig. 2,b shows the fast
Fourier transform (FFT) of the HREM image for the
LPM1A film. The FFT produces a rectangular pattern
of almost circular spots. The measurement of a large
number of interdot spacings allows us to obtain the
average values of the lattice parameters from the
HREM images. Upon the analysis, one can conclude
that the LPM1A film has a pseudocubic crystal struc-
ture with c a� � 0.386 nm, which is in good agree-
ment with the XRD data; here a is the in-plane lattice
parameter.
Figure 3 shows the cross-sectional HREM images
for the LPM2 (a) and the LPM2A (b) films. The inset
A of Fig. 3,a presents the FFT of the HREM image for
the LPM2 film, displaying slightly split and elon-
gated spots in both the c (out-of-plane) and a
(in-plane) directions. These peculiarities of the FFT
pattern indicate the presence of two crystalline phases
with different lattice parameters. The inset B of
Fig. 3,a shows a high-magnification HREM image of
a small region of the LPM2 film. The measurement of
Influence of structural disorder on magnetic and transport properties
Fizika Nizkikh Temperatur, 2005, v. 31, No. 2 215
45 46 47
1.4
1.6
1.8
b
(002)
2
11
2 , degree
46 48
1
2
3
a
(002)
2
1
In
te
n
si
ty
, 1
0
cp
s
3
LA
O
LP
M
1
A
Fig. 1. (a) The (002) XRD peaks for the LPM1 (1) and
the LPM1A (2) films. LAO denotes the substrate peaks.
(b) The (002) XRD peaks for the LPM2 (1) and the
LPM2A (2) films.
Fig. 2. Cross-sectional HREM images for LPM1 (a) and
LPM1A (b) films. The white arrows indicate the edge dis-
locations and the regions with uncrystallized phase. The
inset in (a) is the electron-diffraction pattern for LPM1,
and that in (b) is the FFT of the HREM image for
LPM1A.
a large number of interdot spacings for regions of this
kind located in different areas of the film allows us
to obtain the average values of the lattice parameters
from the HREM images. Upon analysis, one can con-
clude that the LPM2 film consists of two crystal-
line phases with the following lattice parameters:
c a� � 0.388 nm, and c � 0.396 nm and a �
� 0.385 nm, respectively. It is seen that the obtained
results nicely coincide with the XRD data for the
LPM2 film. We will show below that these two crys-
talline phases represent regions of the film with differ-
ent levels of lattice strain. Nonuniformly distributed
lattice strains of this kind have been observed in the
CMR films [19].
Figure 3,b shows that an additional annealing leads
to the removal of lattice strains in the LPM2 film and
to the formation of a perfect crystal structure. The
FFT, presented by the inset of Fig. 3,b, produces a
rectangular pattern of circular and unsplit spots.
A more detailed analysis of the HREM images of
LPM2A shows that the film has a pseudocubic crystal
structure with lattice parameters c a� � 0.387 nm.
Therefore, (La Sr Pr Ca MnO0.7 0.3 0.65 0.35) ( ). .05 05 3 films
with different kinds of crystal structure were pre-
pared, and the magnetic and the transport properties
were investigated: nano-scale disordered (LPM1),
column-like polycrystalline (LPM1A), nonuniformly
strained (LPM2), and single-crystalline strain-free
(LPM2A) films.
3.1. Magnetic and transport properties
Figure 4 presents both the FC (filled dots) and
ZFC (unfilled dots) temperature-dependent magneti-
zation curves for the LPM1 (a), the LPM1A (b), the
LPM2 (c), and the LPM2A (d) films. The LPM1 film
deposited at low substrate temperature shows a typi-
cal paramagnetic M T( ) dependence with a neglible
splitting between the FC and ZFC curves in a mag-
netic field of 500 Oe and with a rapid growth of M as
T � 0. On the other hand, a narrow peak in the mag-
netization was found at TG � 45 K. A slight negative
contribution to the magnetization of the film is pro-
vided by the substrate owing to its diamagnetism,
with an estimated value of the susceptibility
�dia cm g� � � �5 6 10 4 3. / for our case. Figure 4,b
shows that annealing of the film at 740 �C leads to
the formation of a FM state with TC � 240 K. The
LPM2 film exhibits the M T( ) dependence typical for
two-phase magnetic systems (see Fig. 4,c) and repre-
sents a superposition of two magnetic transitions at
TC1 � 270 K and TC2 � 180 K.
It is worth noting that both transition temperatures
are significantly different from those for bare PCMO
(TN � 130 K) [20] and LSMO (TC � 340 K) films
[16]. The results are coincident with the XRD and
216 Fizika Nizkikh Temperatur, 2005, v. 31, No. 2
V.G. Prokhorov et al.
Fig. 3. Cross-sectional HREM images for LPM2 (a) and
LPM2A (b) films. The inset A is the FFT of HREM image
and the inset B is the high-magnification HREM image for
LPM2. The inset in (b) is the FFT of HREM image for
LPM2A.
100 200
0
20
40 c
a
LPM2
ZFC
FC
TC2
TC1
100 200
d
50
100
b
LPM2A
ZFC
FC
TC
TC
T , K
–1.3
–1.2
–1.1
–1.0 TG LPM1
FC
ZFC
50
LPM1AFC
ZFC
M
,1
0
e
m
u
–
5
M
,1
0
e
m
u
–
5
Fig. 4. The FC (filled dots) and ZFC (unfilled dots) mag-
netization curves for the LPM1 (a), the LPM1A (b), the
LPM2 (c), and the LPM2A (d) films. The solid lines are
a guide for the eye.
HREM data, and confirm the presence of two differ-
ent crystalline phases in the film. Annealing at 900 �C
leads to homogenization of these phases and to the
formation of the FM state in the whole film with
TC � 270 K. Figure 4,d shows that the value of the
spontaneous magnetization for the LPM2A film is sig-
nificantly larger than that for the LPM2 film.
Unfortunately, we could not measure R T( ) for the
LPM1 film, since our setting was limited to 107 � and
the resistance was larger than 107 � at room tempera-
ture. Figure 5 displays R T( ) for the LPM1A (a),
LPM2 (b), and LPM2A (c) films without (1) and
with (2) an applied magnetic field of 5 T. The mag-
netic field was directed perpendicular to the transport
current and parallel to the film surface. Figure 5,a
demonstrates that the MI transition in the LPM1A
film occurs at TP � 140 K, which is far below TC for
this film (see Fig. 4,b). R T( ) displays a resistance
minimum at low temperature, which is very often ob-
served in polycrystalline CMR films [22,23]. The po-
sition of the resistance peak for the LPM2 film is
shifted toward higher temperature, TP � 180 K, and
is equal to the temperature of the second magnetic
transition in this film, TC2 � 180 K (see Fig. 4,c).
Figure 5,b shows that the random resistance oscil-
lations appear in the R T( ) curve in a low-temperature
range, which are slightly suppressed under the applied
magnetic field of 5 T. Annealing of the LPM2 film at
900 �C, as is demonstrated in the Fig. 5,c, leads to an
increase of TP � 260 K and to the disappearance of
the resistance oscillations at low temperature. Figure
5,d exhibits the temperature dependence of the nega-
tive magnetoresistance (MR) for the LPM1A (1),
LPM2 (2), and LPM2A (3). The MR value is defined
as 100% · [R R H /R( ) ( )] ( )0 0� , where R( )0 and R H( )
are the resistances with and without a magnetic field
of 5 T, respectively. It is seen that the increase of TP is
accompanied by a decreasing MR effect, which is typi-
cal for the CMR compounds [4,5].
4. Discussion
Let us first consider the magnetic behavior of the
nano-crystalline disordered LPM1 film. Figure 6
shows the in-plane FC M T( ) dependence measured
under an applied magnetic field of 500 Oe. It is seen
that the observed narrow peak at TG � 45 K divides
the M T( ) curve into two temperature ranges with dif-
ferent M T( ) behavior. Below TG the M T( ) curve can
be described in the framework of the Curie—Weiss
(CW) approximation [24]
M T H
C
T
HPM CW( , )
�
�
�
�
�
�
�
��
0 ,
where �0 is a temperature-independent susceptibility,
and the second term is the CW-type susceptibil-
ity with a constant CCW and a characteristic tempe-
rature . Figure 6 demonstrates that the experimental
data for LPM1 can be excellently described by the
CW expression with following parameters: �0 �
� 3 3 10 4 3. � � cm g/ , C /CW � 101 10 2 3. � � cm g, and
� K. The effective moment estimated from CCW
turns out to be �eff � 4.2 �B/Mn, which is almost
coincident with the theoretical value, �eff
theor �
� 4 6. �B/Mn, obtained from following expression [24]:
�eff
theor
� � � � �g xS S x s S{ . [ ( ) ( ) ( )0 5 1 1 11 1 2 2
� � � � �yS S y S S /
1 1 2 2
1 21 1 1( ) ( ) ( )]} .
Here x and y are the Ca and the Sr concentration,
S /1 3 2
and S2 = 2 are the spin values of the Mn4�
and Mn3� ions, respectively, and g = 2 is the Lande
factor. Therefore, one can conclude that the nano-
crystalline disordered LPM1 film is a typical para-
magnet in the temperature range below TG , with a
free motion of the individual Mn spins. On the other
hand, the magnetization decreases sharply and devi-
ates from the CW-type straight line at T TG� . Such
nonlinear behavior of M(T �1) is rather typical for
superparamagnetic (SPM) particles and can be de-
scribed by a Langevin function as [24]
M T H M
H
k T
k T
H
SPM
s
SPM
B
B( , ) coth
�
�
��
�
�
�� �
�
�
�
�
�
�
�
�
,
Influence of structural disorder on magnetic and transport properties
Fizika Nizkikh Temperatur, 2005, v. 31, No. 2 217
10
4
10
4
10
5
Tp
Tp
2
1
a
Tp
2
1
b
100 200
102
10
3
10
3
2
1
c
100 200
d
3
2
1
50
100
T ,K
R
,
�
R
,
�
M
R
,%
R
, �
Fig. 5. The temperature-dependent resistance without (1)
and with (2) an applied magnetic field of 5 T for the
LPM1A (a), the LPM2 (b) and the LPM2A (c) films.
(d) The MR ratio for the LPM1A (1), the LPM2 (2) and
the LPM2A (3) films in an applied magnetic field of 5 T.
where Ms
SPM is the saturation magnetization of the
SPM phase and � is the average magnetic moment of
the SPM particles. The solid line of the inset of Fig. 6
represents a Langevin function giving the best fit to
the experimental data above TG . This line corre-
sponds to the magnetization contribution of SPM par-
ticles having an average moment � � 7500 �B . By
taking 3.4 �B/Mn atom [25] and assuming a spheri-
cal shape of the SPM clusters, with a volume of
�D /3 6, we estimated their average diameter as D �
� 6 nm. Because the estimated diameter is very close
to the crystallite size revealed by the electron diffrac-
tion, one can conclude that these nano-scale disor-
dered crystallites play the role of the superpara-
magnetic particles. The narrow peak found in the
M T( )�1 curve manifests a phase transition from SPM
to PM state, and TG can be interpreted as the temper-
ature for spin-glass (or cluster-glass) freezing.
Figure 4,b shows that the annealing of the na-
no-crystalline disordered LPM1 film leads to its re-
crystallization and to a recovery of FM state. On the
other hand, the large difference between ZFC and FC
magnetization curves and a significant discrepancy be-
tween the MI and FM transition temperatures ma-
nifest the coexistence of the FM metallic and the PM
insulating clusters below TC [26,27]. A similar me-
tastable-phase mixture was observed recently in the
parent (La Pr Ca MnO1 07 03 3�x x) . . compound and ex-
plained by the phase separation effect [14,25]. How-
ever, in our case the phase-mixed state has a metallur-
gical rather than an electronic nature and is related
to the presence of the dislocation networks in the
LPM1A film and the regions of an uncrystallized
phase. Therefore, the MI transition cannot be treated
as a real electronic one but is governed by the percola-
tion of the FM metallic domains [28].
According to the percolation theory, the conductiv-
ity can be expressed as � � �( )p p t
0 , where p is the
concentration of the metallic phase, p0 is its threshold
value in the vicinity of 0.4–0.5 [28], where metallic
filaments are created that permit current transmission
across the sample, and t is the exponent. Figure 7
shows the temperature dependence for both the nor-
malized resistance r R T /R TP
( ) ( ) and spontaneous
magnetization m M T /M
( ) ( )0 for the LPM1A film.
It is seen that the temperature location of the resis-
tance peak, TP , corresponds to m � 0.4, which is coin-
cident with the percolating threshold value and allows
us to use the magnetization as a percolating parameter
for the conducting phase. The inset (b) of Fig. 7 re-
presents the lg versus lg( ) ( )1 0/r m m� plot, where
m0 0 4
. . The solid lines are the fitted curves with fol-
218 Fizika Nizkikh Temperatur, 2005, v. 31, No. 2
V.G. Prokhorov et al.
0.05 0.10
1
2
3
4
PMSPM
T G
T
–1
T
–1
, K
–1
, 10 K
–2 –1
0.5 1.0 1.5
1
2
TG
M
,1
0
e
m
u
/g
–
2
M
,1
0–
e
m
u
/g
2
Fig. 6. M Tversus �1 plot for the LPM1 film under an ap-
plied field of H = 100 Oe. The solid line represents the
CW-type paramagnetic approximation. The inset displays
the same plot above T TG� . The solid line represents a
Langevin function describing the magnetic behavior of
SPM particles.
10
b
21
100 200
0
0.5
1.0
2 1
m0
T , K
0.2 0.3
8.5
a
2
1
T
–1/2
, K
–1/2
0.3 0.4
lg (m–m )0
ln
R
r,
m
,r
e
d
u
ce
u
n
its
TP
lg
(1
/r
) t = 5.3
Fig. 7. r T( ) and m T( ) for the LPM1A film. The circle on
the m T( ) indicates the critical volume of the FM phase
(m0) for the percolating transition. The inset (a) displays
the ln /R Tversus �1 2 plot for the LCP1A film without
(1) and with (2) an applied magnetic field of 5 T. The in-
set (b) displays the lg versus lg( ) ( )1 0/r m m� plot. Solid
lines correspond to the fitting with the percolating expo-
nents t � 5.3 (1) and � 3.6 (2), respectively.
lowing exponents for the percolating conductivity:
t � 5.3 (curve 1) and 3.6 (curve 2). Although the
value t � 3.6 was obtained recently from an analysis
of the MI transition at high magnetic field for
Pr Ca MnO063 037 3. . [29], in our case t � 5.3 is more ap-
propriate for the description of the experimental
curve. This value of t is very close to that obtained by
a numerical calculation for a 3-dimensional system
with spin effects [30]. Therefore, one can conclude
that the MI transition in the LPM1A film has a perco-
lating nature.
The inset (a) of Fig. 7 displays the ln R versus
T �1 2/ plot for the LPM1A film without (curve 1)
and with (2) an applied magnetic field of 5 T. This
plot manifests the exponential growth of resistance at
low temperature, which is described by an expression:
R T /T( ) exp� � . It noteworthy that a similar ex-
pression with an energy gap � � EC, where EC is the
charging energy (or Coulomb barrier), has been pre-
dicted for the conductivity in granular metals [31]
and used to explain the low-temperature R T( ) beha-
vior in ceramic La Sr MnO2 3 1 3 3/ / manganite [32]. Be-
cause the crystalline phase in LPM1A was grown from
the nano-crystalline disordered phase under equilib-
rium thermodynamic conditions, the GBs of this film
contain a higher concentration of edge dislocations
and segregated impurities than those usually observed
in epitaxially grown films, and this results in the for-
mation of an additional small Coulomb barrier. The
value of the charging energy estimated from the slope
of the ln /R Tversus �1 2 plot is EC � 0.0233 meV for
both cases (without and with an applied magnetic
field).
The fact that the value obtained for the charging
energy of the LPM1A film is significantly smaller
than that for ceramic manganites [32] attests to a
better electronic transparency of GBs in this film. On
the other hand, the insensitivity of EC to the applied
magnetic field proves that just the Coulomb barrier is
formed in GBs.
The magnetization data show that the as-deposited
LPM2 film demonstrates the temperature behavior
typical for two-phase systems (see Fig. 4,c). It is
also confirmed by the XRD and the HREM data.
However, a short-term annealing at 900 �C leads
to formation of a single-phase crystal structure (see
Figs. 1,b and 3,b). Our recent investigations of
Pr Ca MnO0.65 0.35 3 films show that annealing at
900 �C for up to 10 hours does not change the chemical
composition of the film (including the oxygen content)
but leads only to relaxation of the lattice strains [20].
Therefore, one can suggest that the main difference
between the LPM2 and the LPM2A films is a different
concentration of the lattice strains only. It is believed
that, owing to a significant lattice mismatch between
the substrate and the film, lattice strains are accumu-
lated in the film during deposition. As reported re-
cently, under a compressive biaxial strain the film
grows in the islands mode, and the strains are distrib-
uted nonuniformly through the sample [19]. The edge
of an island is a region of high strain, while the top of
an island is a region of low strain. Consequently, the
LPM2 film represents a composition of compressive
biaxial strain (c � 0.396 nm and a � 0.385 nm) and
strain-free (c a� � 0.388 nm) crystallites. This is
also confirmed by the fact that the lattice parameters
of the strain-free regions remain practically un-
changed after annealing (c a� � 0.387 nm). There-
fore, the observed two-phase M T( ) behavior of LPM2
(see Fig. 4,c) can be explained by the existence of
these differently strained crystallites. Let us prove
this conjecture to be true on the basis of modern theo-
retical approaches. For weaker strains and a cubic
symmetry TC can be expressed, according to the Millis
model, by [33]:
T TC C B JT( ) ( )� �
� �
� ��
�
�
�
�
�0 1
1
2
2� ,
where � � �B
�( )2 100 001 is a bulk strain, �100
( )a a /afilm bulk bulk� is the in-plane biaxial compres-
sive strain, �001 film bulk bulk
�( )c c /c is the out-
of-plane uniaxial tensile strain, afilm, abulk , cfilm, and
cbulk are the in-plane and out-of-plane lattice para-
meters for the film and the bulk, respectively, �JT
�2 3/ ( )� �001 100 is the Jahn—Teller strain,
( )( )1/T dT /dC C B� , and �
( )( )1 2 2/T d T /dC C JT� .
The magnitudes of
and � represent the relati-
ve weights for the symmetry-conserving bulk and the
symmetry-breaking Jahn—Teller strains, respectively.
According to the theoretical model [33],
� 10 for a
reasonable electron–phonon coupling (0.5 ! 1) in
these compounds, where ! is the electron–phonon in-
teraction constant. If only the relative difference in
the lattice strain between the strain-free and the
strained crystallites is considered, the strain-free pha-
se can be treated as a bulk with c abulk bulk� �
� 0.388 nm. The lattice parameters estimated from
the HREM image (Fig. 3,a) are used for the strained
phase. Using TC for the strain-free phase as
T TC C1 0
( )� � 270 K and the obtained values of
�100 and �001 and TC2 � 180 K for the strained phase
in the LPM2 film, we can obtain � � 1500, which is
almost coincident with the prediction of a theoretical
model [33]. Therefore, one can conclude that the ob-
served magnetic phase separation in the as-deposited
LPM2 film is governed by the nonuniform distribu-
tion of the lattice strains.
Influence of structural disorder on magnetic and transport properties
Fizika Nizkikh Temperatur, 2005, v. 31, No. 2 219
A comparison of the M T( ) and R T( ) curves for the
LPM2 film (see Figs. 4,c and 5,b) demonstrates that
the MI transition occurs at a temperature TP � 180 K,
which is coincident with TC for a lattice strained
phase, TC2 � 180 K. This can be explained by a large
difference in their volumes in the film, which is con-
firmed by the sharp increase in the magnetization (al-
most four times) at T TC 2. Therefore, the concentra-
tion of the FM metallic phase, which appears at the
first magnetic transition of TC1 � 270 K, is insuffi-
cient for the formation of an infinite percolating net-
work in the film, and only a single MI transition is ob-
served on the R T( ) dependence.
The observed random oscillations of resistance in
the LPM2 film at low temperature are probably due to
the presence of the lattice strain, because this effect
disappears after annealing (see Fig. 5). Unfortu-
nately, we did not carry out a detailed investigation of
this phenomenon in this work, but it is worth noting
that a similar effect has recently been observed by us
in the nano-crystalline twinned La Ca MnO065 035 3. .
films [34].
Figures 4,d and 5,c demonstrate that the annealed
LPM2A film undergoes the FM and the MI transitions
at TC � 270 K and TP � 260 K, respectively. The
magnetic and transport characteristics for this
(La Sr Pr Ca MnO07 03 05 065 035 05 3. . . . . .) ( ) film are signifi-
cantly better than those observed for the
La Pr Ca MnO0 4 027 033 3. . . film deposited on LAO [14],
although in our case the concentration of Pr is slightly
larger (La:Pr is 0.52:0.48). We may argue that ob-
served enhancement of the FM and MI transition tem-
peratures is closely related to the substitution of the
Ca ions by the Sr ones. A similar effect was observed
recently in ceramic Pr Ca Sr MnO065 1 035 3. .( )y y� com-
pounds [35]. Therefore, one can conclude that the Sr
ions play a more positive role in these compounds,
leading to an increase of TC, than the Pr ions, which
should suppress the FM ordering.
5. Conclusions
(La Sr Pr Ca MnO07 03 05 065 035 05 3. . . . . .) ( ) films with
different crystal structure have been prepared by a
«co-deposition» utilizing the laser-ablation technique
from two independent PCMO and LSMO targets.
XRD and HREM analysis reveal that the film depos-
ited at a substrate temperature of 300 �C has a
nano-crystalline disordered structure and does not un-
dergo the FM transition in the whole temperature
range. A narrow peak (�T � 10 K) in a tempe-
rature-dependent magnetization was observed at
TG � 45 K, which was interpreted as a PM�SPM
transition. It was shown that the nano-scale crystal-
lites play a role of the superparamagnetic clusters
in the film. The annealing at 750 �C for 1 h in air leads
to a recrystallization of the film and to the appea-
rance of the FM and MI transitions at TC � 240 K and
TP � 140 K, respectively. The observed discrepancy
between TP and TC values is explained by a percolat-
ing nature of the MI transition. The film deposited at
Tsub � 740 �C is composed of the lattice strain-free
and the lattice-strained crystallites with different lat-
tice parameters and TC‘s. The strain-driven change in
TC was consistently described on the basis of the
Millis model [33]. The annealing at 900 �C leads to
the formation of a single-phase crystal structure with
TC � 270 K and TP � 260 K.
This work was supported by the KOSEF through
the Quantum Photonic Science Research Center.
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