STRONG EFFECT OF MULTIPLICITY FLUCTUATIONS IN RARE-EARTH COBALTITES ON MAGNETIC, ELECTRONIC, AND CRYSTAL STRUCTURE PROPERTIES

Abstract

The perovskite compounds ReCoO3-y (Re is Nd, Sm, Gd) have a number of unusual magnetic, electronic, and lattice properties related to the temperature induce spin state crossover from the low spin (LS) to the high spin (HS) states of the Co+3 ions. We have synthesized high quality polycrystalline samples and have measured temperature dependence of the X-ray diffraction, magnetic susceptibility, and lattice dilatation. All observed anomalies are related to the smooth increase of the concentration of the HS ions that are excited over the spin gap between HS and LS terms. Spin gap itself decreases with lattice expansion and goes to zero at the spin crossover temperature. The spin gap is determined by the Re ionic radii.