Magnetic and electronic properties of Hf 2Fe hydrides

Abstract

The intermetallic compound Hf 2Fe forms several hydride phases of different stability up to the composition Hf 2FeH 5. We have studied the hydrogen induced variation of the magnetic and electronic properties of Hf 2Fe using static and dynamic susceptibility measurements and X-ray photoelectron spectroscopy (XPS). The photoelectron spectra revealed a very weak hydrogen induced band, a shift of the hafnium 4d and 4f core levels of 0.6 eV and hardly any shift of the iron core levels, in agreement with strong Hf- H bonding. The magnetic properties of Hf 2FeH x changed from Pauli paramagnetism for x = 0 to Langevin paramagnetism for x = 1.5 to ferromagnetism for x ⩾ 2.5. This behaviour can be explained by the evolution of the iron 2p core levels upon charging with hydrogen. In Hf 2Fe they are rather symmetric in contrast with elemental iron, indicating a weak partial density of iron states at the Fermi level E F owing to a lowering of the iron 3d conduction states below E F . In the hydride, the line asymmetry increases, in agreement with the reappearance of the magnetic moment. At low temperatures and weak magnetic fields we observed magnetic behaviour which characterizes spin glasses: temperature and field dependent irreversible effects in the static susceptibility, a cusp in the temperature dependence of the dynamic susceptibility and a very large typical relaxation time of the magnetization.