Spin dynamics and spin-glass state in Fe-doped cobaltites

Abstract

A thorough study of the magnetic and transport properties of La0.5Sr0.5Co1-xFexO3 (0less than or equal toxless than or equal to0.6) compounds has been made. The Fe substitution destroys the metallic state and the resistivity increases by orders of magnitude even with a very small extent of Fe substitution. The charge localization due to Fe substitution is likely to have its origin in the electronic configuration rather than in its ionic size. The hole-poor regions, corresponding to the Fe-rich regions, would also dilute the magnetic lattice and thereby prevent the occurrence of long-range order. Spin-glass behavior was observed for xgreater than or equal to0.5 compositions and is ascribed to the frustration of random competing exchange interactions, namely the ferromagnetic double-exchange interaction between Co3+ and Co4+, and the antiferromagnetic interactions like Co-O-Fe and Fe-O-Fe. A dynamic scaling analysis of ac susceptibility data using conventional critical slowing down indicates a finite spin-glass phase-transition temperature T(g)approximate to85 K and a dynamic exponent zvapproximate to12.4, for x=0.5 composition. (C) 2004 American Institute of Physics.