Magnetic Properties of K2CuF4—a Transparent Two-Dimensional Ferromagnet—

Abstract

It has been found that K2CuF4is ferromagnetic below 6.25 K. The two-dimensionality of this compound as expected from its K2NiF4type structure is strongly supported by magnetic and specific heat measurements. The torque as well as zero field NMR measurements suggest that the c-plane is an easy plane, in which the spins are very weakly bounded to the direction of a-axis. On the assumption that this magnetic system to be purely two-dimensional, the exchange interaction J between the spins within the c-plane is found to be the Heisenberg type with about one percent XY-like anisotropy and j/k =10.0 K is obtained from the series expansion analysis of the high temperature susceptibility as well as linear dependence of the low temperature specific heat. The transition at 6.25 K may be caused by inter-layer exchange interaction. The exchange field between the adjacent layers is expected at least larger than 400 Oe. © 1972, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.