Third Day Poster Session, 17 June 2010 - NanoTR-VI

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P and
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Poster Session, Thursday, June 17
Theme F686 - N1123
0BElectrical and Magnetic Properties of La
0.67Ca0.33MnO3
SrTiO 3 Nanocomposites
1
1
1
UShailendra Singh RajputUP P*, Leena JoshiP Sunita Keshri (Shaw)P
1
PDepartment of Applied Physics, Birla Institute of Technology, Mesra, Ranchi-835215, India
AbstractA composite series
, has been studied in order to investigate the influence of STO phase on
structural and magneto transport properties of LCMO phase. By X ray diffraction and scanning electron microscopy we find that there is no
interdiffusion between the LCMO and STO phases. The EDX results show that the grains which are smaller in size and mainly distributed at
the grain boundaries and on the surfaces of LCMO grains are of STO phase. Measurements of resistivity on these samples reveal that parent
sample shows a distinct metal insulator transition. The series exhibits a conduction threshold at , up to which extrinsic
transition temperature decreases along with an increase in extrinsic magnetoresistance; whereas above these trends of variation are
reversed. The magnetic phase transitions have been studied by the temperature variation of real () component of AC susceptibility as shown
below. The parent LCMO sample undergoes a PM FM transition at . After addition of STO, remains almost same.
Recently extensive research in nanotechnology and
nanoscience is being carried out worldwide. A
nanocomposite material composed of two different
nanometer-sized crystallites would have significantly
higher contact area between the two compounds, and may
therefore posses an enhanced magneto electric effect. One
of the most serious problems in the practical application of
new manganite colossal magnetoresistance (CMR)
materials remains to be their in sufficient magnetoresistive
(MR) response at room temperature in weak magnetic
fields, used in most of the potentially interesting devices
[1]. Much effort has been made to enhance the properties
of these materials, such as synthesizing CMR–insulator
composites. These extrinsic effects rely on the existence of
an insulating tunneling barrier separating the
ferromagnetic grains. Such attempts include LCMO BTO
[2], LCSMO CoFeR2ROR4R [3] etc and so on. Most of such
results show enhancement in MR. Our previous work has
shown that making LSMO-based composite provides an
efficient way to enhance and control electrical transport
and MR [4]. In present report the magnetic and electric
properties of a series of CMR ferroelectric (FE)
composites have been studied.
A composite series where
= 0.0, 0.10, 0.15, 0.20, 0.30 and 0.40 samples were
prepared in two steps. In this process firstly single phase
LCMO was prepared by pyrophoric method. It was then
mixed with fine powder of STO (Alfa Aesar, 99.99%) in
required ratio and pressed into pellets. The pellets were
Resistivity(cm)
x=0.40
x=0.30
x=0.20
x=0.10
x=0.0
50 100 150 200 250 300
T (K)
Figure 1. Temperature variation of resistivity for composite
finally sintered at 900 C in air for 2 hr, and then slowly
furnace cooled to room temperature..
The XRD and SEM analysis exhibits that the composites
consist of two phases: one is LCMO perovskite phase; the
other is STO phase, which clearly indicates the
coexistence of LCMO and STO phases. The variation of
resistivity as a function of temperature in zero fields for all
composites in the temperature range 10–300K is shown in
Figure 1. The parent LCMO sample shows metal- insulator
(M-I) transition at a temperature
followed by
a broad hump. In all grown composites of this series, a
small peak corresponding to M-I transition of parent
LCMO occurs at 240K. With the increase of STO content
upto to , decreases and resistivity () at
increases as shown in Figure. But for , a reverse
trend is observed, i. e. again increases with a small
decrease in resistivity. The magnetic phase transitions have
been studied by the temperature variation of real ()
component of AC susceptibility. The LCMO sample
undergoes a PM-FM transition at Tc ~270K. After addition
(Arbitrary unit)
x=0.40
x=0.30
x=0.20
x=0.10
x=0.0
0 50 100 150 200 250 300
T (K)
Figure 2. Real part of AC susceptibility for all samples
of BTO, Tc remains almost same indicating that
stoichiometry of LCMO phase within the grains remains
essentially unchanged. Since STO is nonmagnetic in the
measured temperature range, the ferromagnetic order of
the composites comes up only from LCMO.
In summery a nanocomposites series has been prepared
by pyrophoric method. From XRD, and SEM results the
coexistence of both the phases has been confirmed. The
parent sample shows a distinct transition at .
From resistivity data it is concluded that for this series,
conduction threshold occurs at STO content. S.
Keshri gratefully acknowledges Department of Science
and Technology (DST), India for financial assistance. L.
Joshi and S. S. Rajput gratefully acknowledge Council of
Scientific and Industrial Research and DST, India for
providing fellowship, respectively.
* Corresponding author: HTShailendra.phy@gmail.comT
[1] Daughton, J-M., 1999. GMR application, J. Magn. Magn. Mater,
192: 334-342.
[2] Keshri, S., Joshi, L., Rout, S-K., 2009. Influence of BTO phase on
structural, magnetic and electrical properties of LCMO, J. of
Alloys and Compd., 485: 501-506.
[3] Xiong, C-S., et al., 2009. Electrical properties and magnetoelectric
effect measurement in La0R.7RCaR0.2RSrR0.1RMnOR3R/xCoFeR2ROR4R
composites, J. of Alloys and Compd. 474: 316-320.
6th Nanoscience and Nanotechnology Conference, zmir, 2010 750