Magnetic behaviour of the two-dimensional Heisenberg ferromagnetCs2CuF4 under high pressure: a sensitive magnetic measurement in a diamond-anvil cell to26 GPa

Abstract

The isomorphous compounds A2CuF4 (A = K,Rb, Cs) are two-dimensional Heisenberg ferromagnets with the Curie temperatures of 6.25, 6.05 and4.55 K, respectively. Previous studies showed that pressure-induced magnetic phase transitions occurin K2CuF4 and Rb2CuF4 at around 10 GPa, above which the ferromagnetic behaviour disappears as a resultof the structural change from antiferrodistortive to ferrodistortive order of theCuF6 octahedra in thebasal plane. For Cs2CuF4 it was revealed that the interlayer exchange interaction changes fromferromagnetic to antiferromagnetic at a certain pressure below 2.2 GPa. Motivatedby this unexpected result, we have carried out magnetic measurements onCs2CuF4 in a diamond-anvil cell at various pressures up to 26 GPa by using asuperconducting quantum interference device vibrating coil magnetometer.It was found that the Néel temperature increases with pressure at a rate of0.3 K GPa−1 up to 17 GPa, reaches a maximum of about 9 K at around 17 GPa and thendecreases rapidly to zero. At pressures above 21 GPa the magnetic susceptibilitydecreases to the background level, strongly suggesting that a structuralchange similar to those observed for the other two compounds occurs forCs2CuF4 at around this pressure.