Optical properties and ferromagnetic order in K2 CuF4

Abstract

A crystal field analysis of the 3d9 multiplet of Cu+ + in K2CuF4 is presented, taking into account optical absorption spectra, linear dichroism, and the anisotropy of the g tensor. The calculations are based on local D'4h symmetry arising from elongated ligand octahedra with their long axes in the c planes, as it has been proposed theoretically and confirmed by X-ray studies. An additional orthorhombic distortion must be assumed to explain the dichroic properties. Magnetic circular dichroism, Faraday rotation, and magnetic field dependence of the linear birefringence have been used to measure in- and out-of-plane magnetization curves below Tc = 6.25 K. The Faraday rotary dispersion in the visible region and domain effects are discussed