Electronic and Magnetic Properties Due to Co Ions in La0.9Sr0.1Fe1−xCoxO3

Abstract

Variations in physical properties due to Co ions in La0.9Sr0.1Fe1−xCoxO3 (x≤0.5) in which short-range ferromagnetic orders are expected to work predominantly at a rather large x have been investigated so as to elucidate Co states. dc and ac measurements indicate that a hopping process of small polarons dominates electronic conduction, but there is a large reduction in hopping energy when x increases from 0.1 to 0.5. This reduction is related to the structural transition induced by an increase in Co content. A spin-glass phase due to short-range ferromagnetic orders is recognized for x=0.5 in magnetic measurements. A Curie–Weiss relation realized for x=0.5 and comparison of the thermopower extrapolated experimentally at T→∞ with magnitudes estimated theoretically deduce that all or most of Co ions in La0.9Sr0.1Fe1−xCoxO3 are HS Co3+ and IS Co4+ ions.