High field magnetization study of ferrimagnetic arrangements in chromite spinels

Abstract

The observation of a differential susceptibility at high magnetic fields and low temperatures in spinel-type compounds has been shown to be useful for detecting non-collinear ferrimagnetic arrangements. Such an increase in net magnetization with field is not expected for the Néel model of tetrahedral A-site moments antiparallel to octahedral B-site moments. It is, however, expected for the triangular arrangements proposed by Yafet and Kittel in which the moments on one kind of site subdivide into two groups making angles with each other. The latter arrangements have frequently been suggested for chromium-containing spinels, usually on the basis of the observed anomalously low spontaneous magnetizations. Measurements of magnetization curves at 4.2°K in pulsed fields up to 140 kOe reveal high field susceptibilities in MnFe 2 − t Cr t O 4, t > 0; CuCr 2O 4; FeCr 2O 4; and NiFe 2 − t (Cr t O 4, t > 1. These are interpreted as triangular ferrimagnetic arrangements and choices are made between alternative triangular models. In some cases the sign of the dominant anisotropy is suggested. Néel antiparallel ferrimagnetic arrays are confirmed for MnFe 2O 4 and for NiFe 2 − t Cr t O 4, t < 1. The present evidence for these conclusions is of a new and occasionally more direct type.