Magnetic ordering and charge transport in electron-doped La₁-yCeyMnO₃ (0.1 ≤ y ≤ 0.3) films
Microstructure, magnetic and transport properties of the as-deposited La₁−yCeyMnO₃(0.1 ≤ y ≤ 0.3) films, prepared by a pulse laser deposition, have been investigated in wide region of temperature and magnetic field. The microstructure analysis reveals that all films have a high c-oriented texture, t...
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Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України
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| Цитувати: | Magnetic ordering and charge transport in electron-doped La₁-yCeyMnO₃ (0.1 ≤ y ≤ 0.3) films / V.G. Prokhorov, G.G. Kaminsky, V.S. Flis, Y.H. Hyun, S.Y. Park, Y.P. Lee, V.L. Svetchnikov // Физика низких температур. — 2009. — Т. 35, № 6. — С. 593-602. — Бібліогр.: 44 назв. — англ. |
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irk-123456789-1171952017-05-21T03:02:53Z Magnetic ordering and charge transport in electron-doped La₁-yCeyMnO₃ (0.1 ≤ y ≤ 0.3) films Prokhorov, V.G. Kaminsky, G.G. Flis, V.S. Hyun, Y.H. Park, S.Y. Lee, Y.P. Svetchnikov, V.L. Низкотемпеpатуpный магнетизм Microstructure, magnetic and transport properties of the as-deposited La₁−yCeyMnO₃(0.1 ≤ y ≤ 0.3) films, prepared by a pulse laser deposition, have been investigated in wide region of temperature and magnetic field. The microstructure analysis reveals that all films have a high c-oriented texture, the orthorhombic crystal lattice and the negligible quantity of CeO₂ inclusions. The observed strip-domain phase with a periodic spacing of about 3c, the crystal lattice of which is the same to the basic film phase, reveals the magnetic behavior typical for the Griffiths phase. The regions of the double-period modulated phase was found at room temperature in the y = 0.1 film, which are treated as the Mn³⁺/Mn²⁺ ordering with the partial ferromagnetic → antiferromagnetic transition at TN ≤ 80 K. At the same time, the carried out investigation manifests that the magnetic and transport properties of the electron-doped La₁-yCeyMnO₃ films, driven by a cation doping, are similar to that for the hole-doped La/Ca manganites. Therefore, one can conclude, that does not exist of a principle difference between the mechanisms of spin-ordering and charge-transport in the hole- and the electron-doped manganites. 2009 Article Magnetic ordering and charge transport in electron-doped La₁-yCeyMnO₃ (0.1 ≤ y ≤ 0.3) films / V.G. Prokhorov, G.G. Kaminsky, V.S. Flis, Y.H. Hyun, S.Y. Park, Y.P. Lee, V.L. Svetchnikov // Физика низких температур. — 2009. — Т. 35, № 6. — С. 593-602. — Бібліогр.: 44 назв. — англ. 0132-6414 PACS: 71.30.+h, 75.47.Gk, 75.47.Lx http://dspace.nbuv.gov.ua/handle/123456789/117195 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. Kaminsky, G.G. Flis, V.S. Hyun, Y.H. Park, S.Y. Lee, Y.P. Svetchnikov, V.L. Magnetic ordering and charge transport in electron-doped La₁-yCeyMnO₃ (0.1 ≤ y ≤ 0.3) films Физика низких температур |
| description |
Microstructure, magnetic and transport properties of the as-deposited La₁−yCeyMnO₃(0.1 ≤ y ≤ 0.3) films, prepared by a pulse laser deposition, have been investigated in wide region of temperature and magnetic field. The microstructure analysis reveals that all films have a high c-oriented texture, the orthorhombic crystal lattice and the negligible quantity of CeO₂ inclusions. The observed strip-domain phase with a periodic spacing of about 3c, the crystal lattice of which is the same to the basic film phase, reveals the magnetic behavior typical for the Griffiths phase. The regions of the double-period modulated phase was found at room temperature in the y = 0.1 film, which are treated as the Mn³⁺/Mn²⁺ ordering with the partial ferromagnetic → antiferromagnetic transition at TN ≤ 80 K. At the same time, the carried out investigation manifests that the magnetic and transport properties of the electron-doped La₁-yCeyMnO₃ films, driven by a cation doping, are similar to that for the hole-doped La/Ca manganites. Therefore, one can conclude, that does not exist of a principle difference between the mechanisms of spin-ordering and charge-transport in the hole- and the electron-doped manganites. |
| format |
Article |
| author |
Prokhorov, V.G. Kaminsky, G.G. Flis, V.S. Hyun, Y.H. Park, S.Y. Lee, Y.P. Svetchnikov, V.L. |
| author_facet |
Prokhorov, V.G. Kaminsky, G.G. Flis, V.S. Hyun, Y.H. Park, S.Y. Lee, Y.P. Svetchnikov, V.L. |
| author_sort |
Prokhorov, V.G. |
| title |
Magnetic ordering and charge transport in electron-doped La₁-yCeyMnO₃ (0.1 ≤ y ≤ 0.3) films |
| title_short |
Magnetic ordering and charge transport in electron-doped La₁-yCeyMnO₃ (0.1 ≤ y ≤ 0.3) films |
| title_full |
Magnetic ordering and charge transport in electron-doped La₁-yCeyMnO₃ (0.1 ≤ y ≤ 0.3) films |
| title_fullStr |
Magnetic ordering and charge transport in electron-doped La₁-yCeyMnO₃ (0.1 ≤ y ≤ 0.3) films |
| title_full_unstemmed |
Magnetic ordering and charge transport in electron-doped La₁-yCeyMnO₃ (0.1 ≤ y ≤ 0.3) films |
| title_sort |
magnetic ordering and charge transport in electron-doped la₁-yceymno₃ (0.1 ≤ y ≤ 0.3) films |
| publisher |
Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України |
| publishDate |
2009 |
| topic_facet |
Низкотемпеpатуpный магнетизм |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/117195 |
| citation_txt |
Magnetic ordering and charge transport in electron-doped La₁-yCeyMnO₃ (0.1 ≤ y ≤ 0.3) films / V.G. Prokhorov, G.G. Kaminsky, V.S. Flis, Y.H. Hyun, S.Y. Park, Y.P. Lee, V.L. Svetchnikov // Физика низких температур. — 2009. — Т. 35, № 6. — С. 593-602. — Бібліогр.: 44 назв. — англ. |
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Физика низких температур |
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| fulltext |
Fizika Nizkikh Temperatur, 2009, v. 35, No. 6, p. 593–602
Magnetic ordering and charge transport
in electron-doped La1–yCeyMnO3 (0.1 ≤ ≤y 0.3) films
V.G. Prokhorov, G.G. Kaminsky, and V.S. Flis
Institute for Metal Physics, National Academy of Sciences of Ukraine, Kiev 03142, Ukraine
E-mail: pvg@imp.kiev.ua
Y.H. Hyun, S.Y. 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, 2009
Microstructure, magnetic and transport properties of the as-deposited La Ce MnO1 3− y y (0.1 ≤ ≤y 0.3)
films, prepared by a pulse laser deposition, have been investigated in wide region of temperature and
magnetic field. The microstructure analysis reveals that all films have a high c-oriented texture, the
orthorhombic crystal lattice and the negligible quantity of CeO2 inclusions. The observed strip-domain
phase with a periodic spacing of about 3c, the crystal lattice of which is the same to the basic film phase, re-
veals the magnetic behavior typical for the Griffiths phase. The regions of the double-period modulated
phase was found at room temperature in the y = 0.1 film, which are treated as the Mn3+/Mn 2+ ordering with
the partial ferromagnetic → antiferromagnetic transition at TN ≤ 80 K. At the same time, the carried out in-
vestigation manifests that the magnetic and transport properties of the electron-doped La1− yCe yMnO3
films, driven by a cation doping, are similar to that for the hole-doped La/Ca manganites. Therefore, one can
conclude, that does not exist of a principle difference between the mechanisms of spin-ordering and
charge-transport in the hole- and the electron-doped manganites.
PACS: 71.30.+h Metal–insulator transitions and other electronic transitions;
75.47.Gk Colossal magnetoresistance;
75.47.Lx Manganites.
Keywords: manganites, microstructure, magnetization, resistance.
1. Introduction
The hole-doped manganites L 1−xA xMnO 3, where L
and A are a trivalent lanthanide ion and a divalent alka-
line-earth ion, respectively, have attracted considerable
attention due to their interesting fundamental science,
connected with the discovery of colossal magnetoresis-
tance (CMR), and potential for applications [1]. The
transport and magnetic properties of doped manganites
are interpreted as a rule within the framework of «double
exchange» (DE) model which considers the magnetic
coupling between Mn 3+ and Mn 4+ that results from the
motion of an itinerant electron between two partially
filled d shells with strong on-site Hund's coupling [2–4].
However, Millis et al. [5] have shown that DE mechanism
alone cannot explain all aspects of CMR effect, particu-
larly the temperature dependence of resistance, R T( ),
above the metal–insulator (MI) transition temperature.
The authors suggest that a polaron effect due to a strong
electron–phonon coupling arising from the Jahn–Teller
distortion of the Mn 3+ ions is a necessary component for
explaining the details of the R T( ) behavior above the
Curie point (TC ). Taking into account, that while Mn 3+
is a Jahn–Teller ion, Mn 4+ and Mn 2+ are both non-Jahn–
Teller ions, one can expect that the substitution of a triva-
© V.G. Prokhorov, G.G. Kaminsky, V.S. Flis, Y.H. Hyun, S.Y. Park, Y.P. Lee, and V.L. Svetchnikov, 2009
lent lanthanide by a tetravalent element, instead of a diva-
lent one, leads to the same result due to an origin of the
DE between Mn 3+ and Mn 2+ . La 1− yCe yMnO 3 is a typi-
cal electron-doped system which demonstrates the MI
transition and the ferromagnetism (FM) similar to that for
the hole-doped manganites [6]. However, numerical pub-
lications reveal that the single-phase La 1− yCe yMnO 3
compound can be prepared only by the laser-pulse-depo-
sition method at certain technological conditions [7–13].
At the same time, the collected data on the hole-doped
manganites testify that the magnetic and the electronic
phase diagrams of thin films are significantly different
from that for the bulk and, therefore, it is desirable to
perform an additional experimental study.
In this paper we report the experimental results for the
as-deposited La 1− yCe yMnO 3 (0.1 ≤ ≤y 0.3) films, pre-
pared by the laser ablation. It was shown that the mag-
netic and the transport properties of the investigated
films, driven by a cation doping, are very similar to that
for the hole-doped La 1− yCa yMnO 3 system. The ob-
served evidence for the charge-ordered antiferromagnetic
(AFM) state and the Griffiths phase is explained by the
microstructure features of the films.
2. Experimental techniques
A cross-beam laser-ablation technique was employed
for the preparation of the films. A detailed description of
the technique was presented elsewhere [14]. 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 10 8. ⋅ –2 1010⋅ W/cm 2.
The targets were manufactured from the 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 cooling. Under these conditions were grown the
La 0 9. Ce 01. Mn O 3 (LCMO9) , the La 0 8. Ce 0 2. Mn O 3
(LCMO8), and the La 0 7. Ce 0 3. MnO 3 (LCMO7) films with
the same thickness of d � 300 nm. The substrate was a
LaAlO 3 (100) single crystal (LAO) with an out-of-plane
lattice parameter c � 0.379 nm for the pseudocubic sym-
metry. The substrate temperature during deposition was
770 °C, and only the as-deposited films were used for
study. The θ–2θ x-ray diffraction (XRD) patterns were ob-
tained using a Rigaku diffractometer with Cu K α radia-
tion. The lattice parameters evaluated directly from the
XRD data were plotted against cos / sin2 θ θ. From the in-
tercept of the extrapolated straight line to cos / sin2 θ θ =
= 0, a more precise lattice parameter was obtained. The
high-resolution electron-microscopy (HREM) and elec-
tron-diffraction studies were carried out using a Philips
CM300UT-FEG microscope with a field emission gun
operated at 300 kV. The point resolution of the micro-
scope was in the order of 0.12 nm. The cross-sectional
specimens were prepared by the standard techniques us-
ing mechanical polishing followed by ion-beam milling at
a grazing incidence. All microstructure measurements
were carried out at room temperature. The magnetic mea-
surements were performed by using a Quantum Design
SQUID magnetometer. The resistance measurements
were performed by using the four-probe method in a tem-
perature range of 4.2–300 K and in a magnetic field up to
5 T.
3. Microstructure
Figure 1 presents the θ–2θ XRD scans for LCMO9 (a),
LCMO8 (b) and LCMO7 (c) films, which display the
well-defined (00l) Bragg peaks of high intensity for the
films (F) and the LAO substrate (S), indicating that the
deposition results in a highly c-oriented crystal structure.
At the same time, the additional peaks near the 2θ angles
of 33 and 70° are existent, manifesting the presence of
a second phase. Commonly this phase identify as the
unreacted cerium dioxide (CeO 2) impurity, which is more
594 Fizika Nizkikh Temperatur, 2009, v. 35, No. 6
V.G. Prokhorov, G.G. Kaminsky, V.S. Flis, Y.H. Hyun, S.Y. Park, Y.P. Lee, and V.L. Svetchnikov
10
1
10
2
10
3
30 40 50 60 70
10
1
10
3
10
4
10
5
10
1
10
2
10
3
(0
0
1
)
F
/S
(0
0
2
)
C
eO
2
(0
0
2
)
F
/S b
(0
0
3
)
F
/S
(0
0
4
)
C
eO
2
(0
0
1
)
F
/S
In
te
n
si
ty
cp
s
,
In
te
n
si
ty
cp
s
,
In
te
n
si
ty
cp
s
,
c
(0
0
3
)
F
/S
(0
0
4
)
C
eO
(0
0
2
)
F
/S
(0
0
2
)
C
eO
2
2
2 , egθ d
10
2
(0
0
1
)
F
/S
(0
0
2
)
C
eO
2
(0
0
2
)
F
/S
(0
0
3
)
F
/S
(0
0
4
)
C
eO
2
a
Fig. 1. θ–2θ XRD scans for the La1− yCe yMnO3 films with
y = 0.1 (a), 0.2 (b) and 0.3 (c). F and S denote the film and the
substrate, respectively. The Bragg peaks are identified for a
simple pseudocubic symmetry.
stable relative to the basic La 1− yCe yMnO 3 compound. It
is confirmed by the calculated lattice parameter of the
impurity phase from θ–2θ XRD scans, a � 0.543 nm,
which is excellently coincident with the published
results for CeO 2 [15,16]. Analysis of the XRD data for
La 1− yCe yMnO 3 reveals that the out-of-plane lattice pa-
rameter (c) for pseudocubic symmetry slightly decreases
with the Ce doping following to the empirical expression:
c c y= −0 0 005. , where c0 = 0.3885 nm. The found ten-
dency for c completely agrees with the data, which were
obtained for the La 1− yCe yMnO 3 films early [11,12],
and is typical for the hole-doped manganites, such as
La 1− yCa yMnO 3 [17].
Figure 2,a exhibits the low-magnification cross-sec-
tional HREM images of the LCMO9 film, manifesting
that the column-like microstructure is formed during
the deposition with the well-defined sharp and flat in-
terface between film and substrate. The average diameter
of a column turns out to be about 20 nm (see inset
in Fig. 2,a). The carried out HREM study of the LCMO8
and LCMO7 films (not shown) reveals the same co-
lumn-like microstructure. The similar morphological
feature of microstructure has been already observed in
the La 1− yCa yMnO 3 films [18–20], and is explained by a
dislocation-free epitaxial growth mode with the forma-
tion of a strong lattice-strained state. These biaxial strains
accommodate, during the film growth, in forming a co-
herent columnar microstructure directed along interface
normal which can be treated as prismatic antiphase boun-
daries.
The high-magnification cross-sectional HREM image
of LCMO9, represented by Fig. 2,b, shows that the major
part of the film has a perfect crystal lattice. This is con-
firmed by the corresponding fast Fourier transform (FFT)
for this image (see Fig. 2,c), which reveals the almost
rectangular pattern only of basic Bragg spots, typical for
close to the orthorhombic crystal structure. At the same
time, the more careful analysis of a few HREM images
shows that the angle between ortogonal atomic rows is
near 89 2. °, indicating the slight rhombohedral crystal lat-
tice distortion of the LCMO9 film. In contrast to that the
high-magnification HREM images and the FFT patterns
for the LCMO8 and LCMO7 films (not shown) manifest
only the right angle between atomic rows, indicating the
formation of the undistorted orthorhombic crystal lattice.
The analysis of interspot spacings on the FFT patterns and
the HREM images reveals that these films have the fol-
lowing lattice parameters (for pseudocubic symmetry):
c � 0.3887, 0.3877 and 0.3867 nm, and a b� � 0.3814,
0.382 and 0.3823 nm for LCMO9, LCMO8 and LCMO7,
respectively. It is clear that the cross-sectional HREM
analysis can not distinguish difference between a and b
in-plane parameters. In spite of that the obtained lattice
parameters are good coincident with the XRD data.
The main microstructural peculiarity of the LCMO9
film, which is not observed in the LCMO8 and LCMO7
ones (in addition to the rhombohedral distortion), is pres-
ence of the small regions of double-period modulated
Magnetic ordering and charge transport in electron-doped La1–yCeyMnO3 (0.1 ≤ ≤y 0.3) films
Fizika Nizkikh Temperatur, 2009, v. 35, No. 6 595
LCMO9
LAO
30 nm
a
c
c
c*
c*
2a (1/2 00)
(100)
b
d
c
e
2 nm
2 nm
Fig. 2. (a) Low-magnification cross-sectional HREM image
for the La0 9. Ce01. MnO3 film. LAO denotes a substrate. Inset
presents the column-like microstructure with an average diam-
eter of a column about 20 nm (indicated by arrows). [(b) and
(c)] The high-magnification cross-sectional image and the cor-
responding FFT pattern for major part of this film. Only the
fundamental Bragg peaks are indicated. [(d) and (e)] The same
pictures for the modulated phase with the doubled a-axis lat-
tice period parallel to the c-axis direction. The presence of
superlattice spots with a modulation wave vector, similar to
1/2, 0, and 0, is evident.
phase, represented by Fig. 2,d. In this case the FFT of
HREM image (see Fig. 2,e) produces not only a rectangu-
lar pattern of the fundamental Bragg spots, which are typ-
ical for a regular pseudocubic crystal lattice, but addi-
tional superlattice reflections with a wave vector q a= * /2
(indicated by a white circle), where a* is the a-axis re-
ciprocal lattice vector. The similar superlattice spots in
FFT pattern have already been observed for the hole-
doped La 1− yCa yMnO 3 films, including composition of
y = 0.1, and treated as appearance of a charge ordering
of the Mn 4+ and the Mn 3+ ions [21–23]. Like the hole-
doped manganites, there is no sharp boundary between
modulated and unmodulated regions. Instead, one phase
is blended gradually with the other.
The another crystal-lattice imperfections, which are
typical for the all made films, are connected with the pres-
ence of the CeO 2 and, so-called, the strip-domain phases.
Figures 3,a and b display the cross-sectional high-magni-
fication HREM image and the corresponding FFT pattern,
respectively, for the LCMO9 film in the area of the coex-
isting the LCMO9 and the CeO 2 crystalline phases. It is
seen that, in contrast to the modulated and unmodulated
regions, the interphase boundary (indicated by dashed
line) is the very sharp. The orientation relationship
between these phases is [110] CeO2
| | [001] LCMO9, giving
evidence that the crystal lattice of the CeO 2 inclusion is
rotated on angle of 45° against to the matrix LCMO9
phase. The CeO 2 phase does not exceed a few percent of
the film volume and has an average size of 100 nm. Fi-
gures 3,c and b present the HREM image and the FFT pat-
tern for the strip-domain phase, respectively. The similar
long-periodic modulation of crystal structure has already
been observed in the electron- and the hole-doped manga-
nites, and was identified as the nanoclustering CeO 2 do-
mains [13,24] or attributed to a specific ordering of the La
and the doped ions [22,25]. The FFT of the HREM image
for the strip-domain phase (see Fig. 3,d) manifests a rect-
angular pattern of the fundamental Bragg spots, typical
for the matrix LCMO9 phase, and the additional super-
lattice reflections (indicated by white arrows), corre-
sponding to the strip-domain modulation. Therefore, the
strip-domain phase has a crystal structure similar to main
phase of the film, and cannot to identify as the nano-
clustering CeO 2 domains. More preferable seems to be
explanation based on the Wigner-crystal model (or simi-
lar to that), which takes into account the distribution of
the doped ions in the La-based manganites [25–29]. It is
found that La/Ca ordering along with Mn 3+ and Mn 4+
stripes in La1− yCa yMnO 3 is more energetically favor-
able than La/Ca disordering that can lead to formation of
the strip- domain structure, whose domain period, DSD , is
equal to an integer of the crystal lattice parameters. The
FFT pattern in Fig. 3,d reveals that DSD � 3c in our case.
The data of the XRD and the HREM study are summa-
rized in the Table 1.
596 Fizika Nizkikh Temperatur, 2009, v. 35, No. 6
V.G. Prokhorov, G.G. Kaminsky, V.S. Flis, Y.H. Hyun, S.Y. Park, Y.P. Lee, and V.L. Svetchnikov
Table 1. Results of the XRD and the HREM analysis for the investigated films
Samples Crystal
structure
Out-of-plane lattice parameter
c, nm
a
Tetragonal ratio
c a/
Lattice parameter of
CeO2 inclusion, a, nm
XRD intensity ratio
at (002) Bragg peak
XRD HREM data HREM data XRD data I /ICeO Film, %
LCMO9 Rhombohedral 0.388 0.3887 1.02 0.543 0.9
LCMO8 Orthorombic 0.3875 0.3877 1.015 0.544 0.08
LCMO7 Orthorombic 0.387 0.3867 1.012 0.543 0.07
a
For pseudocubic symmetry.
CeO 2
2
LCMO9
a
a
c
a
c
c*
LCMO
c*
CeO
b
c
10 nm
c*
d
(001)
2 nm
Fig. 3. [(a) and (b)] The high-magnification cross-sectional
image and the corresponding FFT pattern for the
La0 9. Ce01. MnO3 film area where the basic and the CeO2
phases coexist. The dashed line indicate the interphase bound-
ary. [(c) and (d)] The same pictures for the strip-domain phase.
The white arrows indicate the period of strip domains in the (c)
real and the (d) reciprocal space. The white square in the (d)
evidences that the strip-domain phase has a crystal lattice of
the basic phase.
4. Experimental results
Figure 4 shows the in-plane field-cooled (FC) (solid
symbols) and the zero-field-cooled (ZFC) (open symbols)
temperature dependences of the magnetic moment, M T( ),
for the LCMO9 (a), LCMO8 (b) and LCMO7 (c) films
at different applied magnetic fields. All films manifest
the ferromagnetic transition at the Curie temperature
TC � 150, 250 and 280 K, for LCMO9, LCMO8 and
LCMO7, respectively. The obtained results are very close
to the published data for the bulk and the as-deposited
films [9–13,24]. The observed splitting between ZFC and
FC M T( ) curves in a low-temperature range at H = 0.01 T
can be explained by the existent difference between an
applied magnetic field direction and the easy magnetiza-
tion axis. Assuming that, in spite of the high c-oriented
texture, the column-like crystallites have a slight disori-
entation to each other in the ab plane, one can conclude
that the easy magnetization axes are randomly oriented,
as well. Therefore, the difference between ZFC and FC
M T( ) curves can be treated as a characteristic of the mi-
Magnetic ordering and charge transport in electron-doped La1–yCeyMnO3 (0.1 ≤ ≤y 0.3) films
Fizika Nizkikh Temperatur, 2009, v. 35, No. 6 597
0
0.5
1.0
1.5
2.0
2.5
3.0
0
0.5
1.0
1.5
2.0
2.5
3.0
50 100 150 200 250
0
0.5
1.0
1.5
2.0
2.5
3.0
y = 0.1 a
0 T
0.01 T
0.05 T
0.1 T
0.5 T
1 T
y = 0.2 b
y = 0.3 c
T K,
M
,
B
/M
n
μ
M
,
B
/M
n
μ
M
,
B
/M
n
μ
Fig. 4. Temperature dependences of the in-plane FC (solid symbols)
and ZFC (open symbols) magnetic moment for the La1− yCe yMnO3
films with y = 0.1 (a), 0.2 (b) and 0.3 (c), measured at different
applied magnetic fields. Lines are guides to the eyes.
–3
–2
–1
0
1
2
3
–3
–2
–1
0
1
2
3
–4 – 2 0 2 4
–3
–2
–1
0
1
2
3
a
y = 0.1
5 K
20 K
100 K
150 K
200 K
b
y = 0.2
c
y = 0.3
TH,
M
,
B
/M
n
μ
M
,
B
/M
n
μ
M
,
B
/M
n
μ
Fig. 5. Magnetic-field dependences of the in-plane magnetic
moment for the La1− yCe yMnO3 films with y = 0.1 (a), 0.2 (b)
and 0.3 (c), measured at different temperatures. Lines are gui-
des to the eyes.
crostructure perfection, which is higher for the LCMO8
film.
Figure 5 presents the in-plane hysteresis loops, M H( ),
for the LCMO9 (a), LCMO8 (b) and LCMO7 (c) films
taken at different temperatures. All films have almost the
similar value of the saturation magnetic moment at 5 K,
near 3.3 μ B /Mn, which is higher than that was observed
for the post-annealed films [24] while quite smaller of
predicted by the theory [30]. It is seen more clearly on the
temperature dependences of the saturation magnetic mo-
ment, M Ts( ), represented by Fig. 6,a.
Figure 6,b displays the in-plane hysteresis loops at 5 K
for the films more in detail, which were measured in
the ZFC (open symbols) and the FC (solid symbols)
regimes. In last case the films were cooled down in the ex-
ternal magnetic field of 0.5 T. This experiment was car-
ried out for the feature testing of the exchange-bias-inter-
action effect, which has been observed in the hole-doped
La 0 7. Ca 0 3. MnO 3 compound [31,32]. The main obvious
indication of the existence of exchange bias is the shift of
the hysteresis loop along the field axis after field cooling
of the sample. However, in our case the hysteresis loops
are symmetrical regardless of the cooling regime with a
coercive field of H c � ± 216, 83 and 167 Oe at T = 5 K for
LCMO9, LCMO8 and LCMO7, respectively. Moreover,
all films have almost the same remanent magnetic mo-
ment, M r � 2.0 μ B /Mn, at this temperature. The observed
minimal H c value for LCMO8 can be is explained by the
more perfect microstructure which is realized in this film,
as was mentioned above.
Figures 7 shows the temperature dependence of re-
sistance, R(T ), for the LCMO9 (a), LCMO8 (b) and
598 Fizika Nizkikh Temperatur, 2009, v. 35, No. 6
V.G. Prokhorov, G.G. Kaminsky, V.S. Flis, Y.H. Hyun, S.Y. Park, Y.P. Lee, and V.L. Svetchnikov
–400 – 200 0 200 400
–2
–1
0
1
2
50 100 150 200
0
1
2
3
b
5 K
y
0.1
0.2
0.3
a
0.3
0.2
y = 0.1
T K,
H, Oe
M
,
B
/M
n
μ
M
s
,
B
/M
n
μ
Fig. 6. (a) Temperature dependence of the in-plane saturation
magnetic moment for the La1− yCe yMnO3 films. Lines are
guides to the eyes. (b) The in-plane ZFC (open symbols) and
FC (solid symbols) hysteresis loops for the same films mea-
sured at 5 K. The films were cooled down at H = 0.5 T.
10 3
10 4
10 5
10 6
10 2
10 3
50 100 150 200 250
10
2
10 3
100 200
0
100
200
100 200
0
250
500
100 200
0
200
400
a
R
,
Ω
R
,
Ω
R
,
Ω
0 T
1 T
3 T
5 T
b
c
T K,
T K,
T K,
T K,
y = 0.1
M
R
%
,
y = 0.2
M
R
%
,
y = 0.3
M
R
%
,
Fig. 7. Temperature dependence of resistance for the
La1− yCe yMnO3 films with y = 0.1 (a), 0.2 (b) and 0.3 (c),
measured at different applied magnetic fields. Lines are guides
to the eyes. Insets show the corresponding temperature depen-
dences of the magnetoresistance, MR (%).
LCMO7 (c) films measured at different applied magnetic
fields. The magnetic field was directed parallel to the film
surface and at right angle to the transport current. The in-
sets presents the temperature-dependent magnetoresis-
tance ratio, MR, for the corresponding films. Here the MR
value is defined by 100% × [R(0) – R(H)]/R(H), where
R(0) and R(H) are the resistances without and with a mag-
netic field of 5 T, respectively. It is seen that LCMO9 does
not undergo the sharp transition in the metal state with de-
creasing temperature in the whole temperature interval
while demonstrates the significant increase of MR(T )
with the slight kink-like peculiarity near the Curie point,
TC � 150 K (indicated by arrow). In contrast to that
LCMO8 and LCMO7 manifest a typical for CMR R(T ) be-
havior with the well-defined metal–insulator (MI) transition
at TP � 225 and 245 K and MR � 600 and 440%, respec-
tively.
The main physical parameters of the films are summa-
rized in Table 2.
5. Discussion
The magnetic and transport properties of the investi-
gated La 1− yCe yMnO 3 films are very similar to that for
La 1− yCa yMnO 3 system. The decrease in Ce or Ca dop-
ing up to y = 0.1 leads to suppression of ferromagnetic or-
dering, which is accompanied by a significant decreasing
of TC , and a disappearance of the MI transition at all tem-
peratures. Figure 8,a presents the M(T ) dependence of the
spontaneous magnetization (without an applied magnetic
field) for LCMO9. It is seen that after the well-defined in-
crease of magnetic moment, which is connected with the
FM transition at TC ≤ 150 K, the M(T ) begin to drop with
decreasing temperature at T ≤ 80 K. The evidence of the
low-temperature magnetic transition is confirmed by the
non-monotonic temperature behavior of the MR(T ),
which is represented by Fig. 8,b. In addition to the
kink-like peculiarity at TC , the MR(T ) curve demon-
strates a sharp bend at T ≤ 80 K, indicating that the mag-
netic state of film is changed with decreasing tempera-
ture. For the La/Ca system of the same composition this
phenomenon is explained by existence of the second fer-
romagnetic → canted antiferromagnetic transition which
supervenes FM at once [33,34]. This explanation can be
used for description of magnetic behavior in the elec-
tron-doped LCMO9 film, as well. The FFT pattern (see
Fig. 2,e) for this film presents the small regions of dou-
ble-period modulated phase with a wave vector q a= * / 2,
Magnetic ordering and charge transport in electron-doped La1–yCeyMnO3 (0.1 ≤ ≤y 0.3) films
Fizika Nizkikh Temperatur, 2009, v. 35, No. 6 599
Table 2. Magnetotransport characteristics for the investigated films
Samples Curie point,
TC , K
Coercive field,
Hc, Oe
Remanence,
Mr Ms/ , %
Magnetoresistance,
MR, %
a
MI transition,
TP , K
Activation energy,
EA , K
LCMO9 150 216 63 200 — 1700
LCMO8 250 83 58 600 225 1600
LSMO7 280 167 64 440 245 1400
a
Maximal value at TP, for LCMO9 at TC .
50 100 150
0.05
0.10
0.15
0.20
0.25
–500 0 500
–2
–1
0
1
2
100 150 200 250
0
100
200
300
H = 0
y = 0.1
y = 0.1
200 K
H Oe,
1 T
3 T
5 T
T K,
T K,
T
C
T
N
a
T
N
T
C
T
G
b
M
,
B
/M
n
μ
M
,
1
0
–
2
B
/M
n
μ
M
R
,
%
Fig. 8. (a) Temperature dependences of the spontaneous
magnetization (without an applied magnetic field) for the
La Ce MnO0.9 0.1 3 film. Arrows indicate the FM (TC) and the
AFM (TN ) transition temperatures. Inset presents the M H( ) de-
pendence for the same film taken at T = 200 K, which is signi-
ficantly higher than Curie point. Lines are guides to the eyes.
(b) Temperature dependences of magnetoresistance ratio at dif-
ferent applied magnetic fields. Arrows indicate the peculiari-
ties on the MR(T) curves, connected with the corresponding
magnetic transitions. TG is the Griffiths temperature (see text).
which usually is treated as a formation of the charge-or-
dered antiferromagnetic (AFM) state (with the ordering
of Mn 2+ and Mn 3+ ions). Consequently, the FM and the
charge-ordered AFM phases are coexisted in the LCMO9
film at low temperatures (T ≤ 80 K). However, in contrast
to a well-known intrinsic phase-separation effect, which
is very often observed in the hole-doped manganites and
has an electronic origin [1], in our case these magnetic
phases belong to the different crystal structures (mo-
dulated and unmodulated), which are controlled by the
long-range Jahn–Teller interaction and arise due to a
nonuniform distribution of the lattice strain during an
epitaxial growth mode [21,22,35]. The HREM analysis
reveals that the double-period modulated (AFM) phase,
does not exceed a few percent of the film volume, and can
not to have a serious influence on the total magnetic pro-
perties of the film. It is confirmed by the minor difference
in the saturation magnetic moment at low temperature
between films with a different Ce doping (see Fig. 6,a).
At the same time, another kind of the magnetic in-
homogeneity is existent in LCMO9 film. Inset in Fig. 8,a
presents the M H( ) dependence for LCMO9, taken at tem-
perature, which is significantly higher than Curie point.
The hysteretic behavior of the magnetization loop evi-
dences the presence a few of the FM phase in the tempera-
ture range, where the film must be in the paramagnetic
(PM) basic state. The chemical inhomogeneity of the film
and the existence of long-term spin-ordered fluctuations
(magnetic polaron clusters), can be main reasons for
this phenomenon. It was shown recently that in
La 0 9. Ce 01. MnO 3 film, deposited at the high oxygen pres-
sure, Curie temperature reaches of 200 K [12]. The more
reasonable explanation of this effect is based on the influ-
ence of the oxygen doping on the Mn 3+ : Mn 2+ ratio,
which provides the magnetic ordering and the electron
transport in these compounds. The ionic structure of this
manganite according to Jonker and van Santen [36] is
La 1
3
−
+
yCe y
4+ Mn
1 2
3
− +
+
y δ Mn
y−
+
2
2
δ O
3
2
−
−
δ V δ
O, where V δ
O stands
for the ratio of oxygen vacancies. Consequently, the real
Mn 3+ : Mn 2+ ratio is significantly dependent on the oxy-
gen content. The oxygen deficiency leads to increase of
the Mn 3+ : Mn 2+ ratio ( y → 0) while the overdoping by
oxygen reveals the decreasing Mn 3+ : Mn 2+ ( y → 1).
Therefore, the La 0 9. Ce 01. MnO 3 film, prepared at the high
oxygen pressure [12], can not be treated as an exactly cor-
responding to the indicated stoichiometry, and the ob-
served enhancement of FM ordering (increase of TC ) is
governed by the increase in concentration of Mn 2+ . On
the other hand, the HREM analysis reveals the presents of
regions with a strip-domain phase (see Fig. 3,c), which
can be treated as a low-dimensional layered structure.
The main peculiarity of such kind of structure is the exis-
tence of long-term spin-ordered fluctuations (magne-
tic polaron clusters) [37], which leads to the Griffiths
phase [38] formation above the FM transition point.
In this case the magnetic moment can be written as
M T H M H k T HB( , ) ( , ) exp ( / )= −0 μeff , where M H( , )0 is
the magnetic moment at T = 0, k B is the Boltzmann
constant, and μeff is the effective magnetic moment of
magnetic polaron cluster. Figure 9,a shows the M T( )
dependences for LCMO9 in the temperature range above
Curie point at different applied magnetic fields. The solid
lines are the corresponding theoretical curves, obtained
within the framework of magnetic polaron model [37].
It is seen that the theoretical curves excellently agree with
experimental ones up to about T � 300 K, above which
600 Fizika Nizkikh Temperatur, 2009, v. 35, No. 6
V.G. Prokhorov, G.G. Kaminsky, V.S. Flis, Y.H. Hyun, S.Y. Park, Y.P. Lee, and V.L. Svetchnikov
3.4 3.5 3.6
0.8
1.0
1.2
1.4
1.6
150 200 250
10
–3
10
–2
10
–1
10
0
b
y = 0.3
y = 0.1
y = 0.2
ln
(R
/T
),
Ω
/K
T ,
–1
10
–3
K
–1
a
0.01 T
0.1 T
0.5 T
1 T
T, K
M
,
B
/M
n
μ
Fig. 9. (a) Temperature dependence of the in-plane FC mag-
netic moment for the LCMO9 film in the temperature range
above Curie point at different applied magnetic fields. The
solid lines are the corresponding theoretical curves, obtained
within the framework of magnetic polaron model (see discus-
sion in the text). (b) The ln (R T/ ) vs. T −1 plots for the
La1− yCe yMnO3 films in temperature range above the corre-
sponding Curie points. Solid lines are theoretical curves, ob-
tained on basis of thermally-activated conductivity model (see
discussion in the text).
the film transforms to the true PM state. Consequent-
ly, this temperature can be treated as the Griffiths one,
TG � 300 K, and the temperature range between TC and
TG is the area of existence of the Griffiths phase [39].
To avoid the PM contribution in magnetic moment, only
the M T( ) curve, taken at lower magnetic field, is ana-
lyzed in detail. The following fitting parameters were
obtained in this case: M H( , )0 � 0.4μ B /Mn site and
μeff � 7 5 10 3. ⋅ μ B . By taking the saturation magnetic mo-
ment for the fully-FM state in this film as 3.3μ B /Mn, the
estimated average diameter of a magnetic polaron cluster
in the Griffiths phase turns out to be 6.2 nm, which is very
close to that for the La 0 4. Ca 0 6. MnO 3 film with inclusions
of the similar strip-domain phase [22]. Figures 8,b mani-
fests that the magnetoresistance effect for the LCMO9
film occurs at T TG≤ , in other words in the Griffiths state,
but without the MI transition below TC with the decreas-
ing temperature. First fact once more confirms the exis-
tence of long-term spin-ordered fluctuations at T TC≥
and the second one is explained by the deficiency of an
itinerant electrons, which are necessary for formation of
the conducting channel or the infinite cluster for theirs
percolation [1].
Analysis of the HREM images for LCMO8 and
LCMO7 (not shown) reveals that these films also have re-
gions with the strip-domain phase and, as result, should
be demonstrate the magnetic behavior typical for the
Griffiths phase at T TC≥ . However, since our setting
was limited to room temperature, we could not carry out
the M T( ) measurements in the temperature interval far
higher of Curie points and realize the careful test of this
assumption.
Figure 9 shows the (ln /R T ) vs. T −1 plots in tempe-
rature range above the corresponding Curie points for
the LCMO9, LCMO8 and LCMO7 films. These plots
can be described on the basis of thermally-activated
conductivity model which predicts an expression of
R T R T E TA( ) exp ( / )= 0 where E A is the activation en-
ergy in unit of temperature. The best agreement between
the experiment and the theory (solid lines) is seen with the
activation energy values as T A � 1700, 1600 and 1400 K
for LCMO9, LCMO8 and LCMO7, respectively. These
values are very close to that for the La/Ca films and testify
to the thermally-activated polaron mechanism of the
conductivity in the PM state.
6. Conclusions
The electron-doped La 1− yCe yMnO 3 films ( y = 0.1,
0.2 and 0.3) have been prepared by the pulse laser deposi-
tion on the LaAlO 3 (100) substrate. The microstructure
analysis reveals that all films have a high c-oriented tex-
ture, the orthorhombic crystal lattice, excepting of y =
= 0.1, which manifests a slight rhombohedral distortion,
and the negligible quantity of CeO 2 inclusions. The ob-
served strip-domain phase with a periodic spacing of
about 3c, the crystal lattice of which is the same to the ba-
sic film phase, reveals the magnetic behavior typical for
the Griffiths phase. The regions of the double-period
modulated phase was found at room temperature in the
y = 0.1 film, which are treated as the Mn 3+ /Mn 2+ order-
ing with the partial FM → AFM transition at TN ≤ 80 K.
At the same time, the carried out investigation manifests
that the magnetic and transport properties of the elec-
tron-doped La 1− yCe yMnO 3 films, driven by a cation
doping, are similar to that for the hole-doped La/Ca man-
ganites. Therefore, one can conclude, that does not exist
of principle difference between the mechanisms of spin-
ordering and charge-transport in the hole- and the elect-
ron-doped manganites.
Acknowledgments
This work was supported by the KOSEF through the
Quantum Photonic Science Research Center, Korea. V.
Svetchnikov is grateful to the financial support of Nether-
lands Institute for Metal Research.
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