Thermoelectric Properties of Fe0.2Co3.8Sb12-xTex ... - Physics
Thermoelectric Properties of Fe0.2Co3.8Sb12-xTex ... - Physics
Thermoelectric Properties of Fe0.2Co3.8Sb12-xTex ... - Physics
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Abstract<br />
In Search for the Origin <strong>of</strong> Glassiness in La 0.85 Sr 0.15 CoO 3<br />
Kaustuv Manna<br />
Department <strong>of</strong> <strong>Physics</strong>, Indian Institute <strong>of</strong> Science, Bangalore- 560012, India<br />
The magnetic behavior <strong>of</strong> La0.85Sr0.15CoO3 has been subjected to a controversial<br />
debate for the last several years; while some groups show evidence for phaseseparation<br />
(PS), others show spin-glass (SG) behavior. Here, we present a<br />
comprehensive investigation <strong>of</strong> the structural, ac susceptibility, dc magnetization and<br />
neutron diffraction studies on two sets <strong>of</strong> La0.85Sr0.15CoO3 polycrystalline samples<br />
prepared from the same initial mixture but subjected to different heat treatment<br />
processes. The dc magnetization study, done on both the samples show a kink in the<br />
field-cooled magnetization and a peak in the zero-field-cooled magnetization which<br />
shifts to the lower temperature at modest dc fields following an AT line behavior. In<br />
addition, the ac susceptibility study exhibits a frequency dependent peak shift (~ 4 K)<br />
which follows Volgel-Fulcher law, time-dependent memory effect, and a spin<br />
relaxation time τo~10 -13 s; all <strong>of</strong> which strongly indicate the characteristics <strong>of</strong> the SG<br />
behavior. The neutron depolarization measurement done on the conventionally<br />
prepared La0.85Sr0.15CoO3 sample clearly shows the existence <strong>of</strong> ferromagnetic clusters<br />
embedded in a non-ferromagnetic matrix. But, once the same sample is properly<br />
homogenized by the repeated grinding and annealing process, these clusters<br />
disappears and the sample turns to a pure SG phase with zero depolarization <strong>of</strong> the<br />
transmitted neutron beam. Thus, our comparative study clearly reveals that the phaseseparated<br />
nature is not intrinsic to La 0.85 Sr 0.15 CoO 3 system; in fact this is an outcome<br />
<strong>of</strong> the compositional inhomogeneity. In essence, all the present experimental findings<br />
evidence that the true ground state magnetic property <strong>of</strong> La0.85Sr0.15CoO3 is spin-glass<br />
in nature.<br />
References:<br />
1. Kaustuv Manna, D. Samal, Suja Elizabeth, H. L. Bhat, and P.S. Anil Kumar<br />
The Journal <strong>of</strong> Physical Chemistry C, (2011) 115, 13985-13990.<br />
2. Kaustuv Manna, D. Samal, Suja Elizabeth, H. L. Bhat, and P.S. Anil Kumar<br />
Journal <strong>of</strong> Superconductivity and Novel Magnetism, (2011) 24, 833–837.
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