Exchange Coupling of Neighboring Mn++ Ions in Mn++:ZnS Crystals

Abstract

The magnetic susceptibilities have been measured over the temperature range of 20°–800°K for five ZnS crystals doped with Mn⁺⁺ in varying concentrations from 0.5% to 7.5%. Above 77°K the magnetic data show considerable deviation from Curie's law which can be explained by the antiferromagnetic coupling between the Mn⁺⁺ ions situated at the nearest neighboring cation sites in the ZnS crystal. To account for the experimental results quantitatively, it is assumed that the numbers of clusters of various types are determined by statistics of random distribution and that the exchange operator can be taken as the simple isotropic form −2J (s₁·s₂). The observed susceptibilities can then be fitted to the theoretical values using J=−9±1 cm⁻¹. Additional terms of the exchange operator such as the next‐nearest neighbor interaction, anisotropic exchange, and the biquadratic coupling term are discussed.