The metamagnetic and the weak ferromagnetic transitions of the Cu lattice of Ho2CuO4

Abstract

We have studied the magnetic properties of the Cu lattice of Ho2CuO4. This cuprate can only be synthesized at high pressure. It crystallizes in a structure derived from the Nd2CuO4-type structure (T′ phase), modified by local distortions in the CuO2 planes. We have measured dc magnetization versus temperature and isothermal dc magnetization versus magnetic field. These measurements were made in the range of temperature from 5 to 540 K applying magnetic fields up to ±50 kOe. ac susceptibility has also been measured in the range of temperatures from 80 to 320 K, using different frequencies between 33 and 1000 Hz and excitation fields between 1 and 10 Oe. We have found a three-dimensional antiferromagnetic (AF) ordering of the Cu lattice of Ho2CuO4 below TN=271(1) K. This AF order is accompanied by a weak ferromagnetic (WF) component, due to a small canting of the Cu spins away from perfect AF alignment. Below TN, at zero field, the interlayer AF coupling makes the WF components in neighboring CuO2 planes to be oriented antiferromagnetically and, thus, to remain almost compensated. Only above a field-induced metamagnetic transition is the weak ferromagnetism evidenced. The WF component persists above TN, in a large temperature interval, induced by the magnetic field. The magnetization of the paramagnetic (PM) Ho lattice, which follows a Curie–Weiss law with μeff=10.16(1)μB/Ho atom and θ=7.6(5) K, is superimposed to the magnetism of the Cu lattice. There exists an exchange coupling between both lattices and the PM Ho ions are polarized through an internal magnetic field due to the WF component of the Cu moments.