Consideration on Four-Spin Exchange Interactions in fcc Spin Lattice with Particular Reference to NiS₂

Abstract

Four-spin exchange interactions in fcc spin lattice are investigated for the purpose of understanding anomalous magnetic properties of NiS 2 with pyrite structure. It is shown that a phase transition is possible from the ordered phase with the first-kind spin ordering to the other ordered phase in which the second-kind ordering coexists with the first-kind ordering. Furthermore, this low temperature phase is expected also to have weak ferromagnetism induced by crystal-line anisotropy.