Pressure-induced magnetic phase transition in the two-dimensional Heisenberg ferromagnet K 2CuF 4

Abstract

A pressure-induced magnetic phase transition in K 2CuF 4 was investigated up to 13 GPa. We observed a sudden decrease in the Curie temperature starting from 7 GPa and a large decrease in the susceptibility above 10 GPa. High-pressure powder X-ray diffraction studies were also made at room temperature up to 14 GPa to investigate such a drastic change in magnetism from structural point of view. A structural phase transition was observed at around 9.5 GPa, above which the CuF 6 octahedra were found to be in the ferrodistortive (FD) order with the elongated axes in the basal plane. As magnetic and structural changes occur at nearly the same pressure, the observed change in the magnetism suggests a ferromagnetic-to-antiferromagnetic phase transition resulting from the distortive change in the basal plane if the critical pressure is assumed not to change so much in the temperature range investigated.