Resistive transition, anomalous magnetocapacitance, and ferroelectric
phenomena observed in charge ordered canted antiferromagnetic
La
0.5
Ba
0.5
FeO
3
perovskite
Md G. Masud,
1
Arijit Ghosh,
1
B. K. Chaudhuri,
1,2,a)
K. Hsiao,
2
and H. D. Yang
2
1
Solid State Physics Department, Indian Association for the Cultivation of Science, Kolkata-700032, India
2
Department of Physics and Center for Nanoscience and Nanotechnology, National Sun Yat-Sen University,
Kaohsiung 804, Taiwan
(Received 20 September 2011; accepted 31 October 2011; published online 12 December 2011)
We report multifunctional properties of the charge disproportionate correlated electronic system
La
0.5
Ba
0.5
FeO
3
synthesized by conventional solid state reaction route. The bulk sample undergoes
semiconductor–metal like transition at T
SM
¼ 102 K showing appreciable magnetoresistance
($20%) around T
SM
even at a low field ($0.5 T). A crossover of electrical conduction mechanism
from Mott’s variable range hopping to small polaron hopping occurs around 210 K, well above
T
SM
. Analysis of the transport, magnetic susceptibility, and magnetization data in the light of de
Gennes proposal indicates the formation of canted antiferromagnetic spin order preceded by charge
ordering in La
0.5
Ba
0.5
FeO
3
. Nonsaturation behavior and nonlinearity of the M-H curve at low
temperature and at high field ($5 T), confirms the canted spin order. The observed resistive
transition is considered to be associated with the onset of weak ferromagnetic ordering in the
canted antiferromagnetic spin state of the materials. Moreover, novel ferroelectric like behavior
showing electric field-polarization hysteresis loop below the charge ordering temperature along
with anomalous magnetocapacitance response representing magnetoelectric coupling is also
observed. In the low temperature regime spin lattice coupling might be responsible for exhibiting
magnetocapacitance in La
0.5
Ba
0.5
FeO
3.
Such multifunctional character implies fundamental as well
as technological importance of this sample.
V
C
2011 American Institute of Physics.
[doi:10.1063/1.3665648]
I. INTRODUCTION
Many strongly correlated 3d transition metal oxides
(TMOs) are found to show intriguing magnetotransport
properties.
1–3
The interplay among spin, charge and orbital
degrees of freedom in some multicomponent TMOs yields
striking physical phenomena, like metal insulator transitions,
colossal magnetoresistance,
4–8
magnetoelectricity,
9
or multi-
ferroicity,
6
etc. Iron ion containing La
1/3
Sr
2/3
FeO
3
, and
La
1-x
Ba
x
FeO
3
perovskite type systems possess unique charge
disproportionate (CD) character.
10,11
In such cases, a charge
state is separated into two (or more) differently charged
states as 2Fe
3þ
!Fe
4þ
þ Fe
2þ
. The distribution of various
valence iron ions and the interaction among them are respon-
sible for inducing many interesting physical phenomena
such as structural change, charge and orbital ordering, and
spin/cluster glass behaviors, etc.
12–17
around the correspond-
ing charge disproportionate temperature T
CD
. Interesting
pressure induced metal insulator transition has also been
observed in charge disproportionate CaFeO
3
and Sr
3
Fe
2
O
7
(Refs. 18 and 19] where electronic ground states transform
to complicated magnetic structure like charge uniform ferro-
magnetic metal to helical and collinear spin structure antifer-
romagnetic metal and insulator,
18,19
etc. Enormous changes
in the distribution of various valence iron ions and the
interaction among them might also occur on doping at appro-
priate sites in the parent system like CaFeO
3,
LaFeO
3
.
LaFeO
3
, for instance, is orthorhombic at room temperature
[space group Pbnm (Ref. 21)]. By “Ba” doping at the “La”
site (i.e., La
0.5
Ba
0.5
FeO
3
, hereafter denoted by LBFO), it
becomes cubic (space group Pm-3 m) at room temperature.
20
Such doping induce transition is also associated with appre-
ciable modification of physical properties due to change of
spin structure in the system. The magnetic order is weakened
by substitution of trivalent “La” site by divalent “Ba”, which
forces “Fe” from stable trivalent to the rare tetravalent state
producing charge disproportion. Observation of metal insula-
tor like transition in this system similarly to those of many
mixed valent rare earth manganites
7,8
is a possibility yet to
be explored. Recently we reported
22
high dielectric permit-
tivity and room temperature magnetodielectric response in
the electrically heterogeneous sample of La
0.5
Ba
0.5
FeO
3.
Zhang et al.
20
also observed interesting magnetic phase tran-
sition at low temperature under external pressure in the same
system. Resistivity data of La
0.5
Ba
0.5
FeO
3
showed
20
variable
range hopping (VRH) behavior, however, no semiconductor–
metal (SM) like transition, charge ordering induced ferroelec-
tricity, or the presence of magnetoelectric coupling was
reported in such a system.
In this paper we report the result of our thoroughly
investigation of the temperature dependent transport and
magnetic properties of the CD system La
0.5
Ba
0.5
FeO
3
(LBFO) exhibiting interesting multifunctional behavior
a)
Author to whom correspondence should be addressed. Electronic mail:
sspbkc@rediffmail.com.
0021-8979/2011/110(11)/113719/6/$30.00
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2011 American Institute of Physics110, 113719-1
JOURNAL OF APPLIED PHYSICS 110, 113719 (2011)