EPR Study of Crystal Defects in SmS

Abstract

A three-line high-field EPR signal was observed at 4 K in stoichiometric SmS single crystals. As Walsh et al., we attribute these signals to Sm3+ ions neighbouring a crystal defect.These spins are shown to be embedded in a square symmetry. We treat a formalism for a 8 spin in such a symmetry which leads us to express the g-factors as a function of one single anisotropy parameter. Comparing this model with the experimental data, and examining the widths of the lines, we deduce the value of the exchange constant with the Sm2+ neighbours and that the defect has two near configurations, both not far from cubic symmetry.The high-pressure intermediate valence and so-called <<golden phase. of SmS has been intensively studied in these last 10 years. But the low-pressure <<black phase. which is semiconducting, is not so well known. The previous works on this topic [ll and more recent papers [2, 31 have shown that this phase has interesting transport properties: a semimetallic f -d configuration at low temperature and high pressure, and metastable effects which seem to be due to magnetic polarons bound on crystal defects. From this point of view, it is of great importance to understand the nature and the configuration of these defects; EPR is an appropriate experimental tool for this kind of studies, and we present here some results based on such measurements.