Investigation of alpha -ErHxsingle crystals in the magnetically ordered range by resistivity measurements: observation of gap-like behaviour in the spin-wave spectrum

Abstract

The temperature dependence of the electrical resistivity of monocrystalline alpha -ErHx has been measured for x=0, 0.01, 0.02, 0.04, 0.06, 0.08 and 0.11 at. H/at. Er parallel to the c axis and for x=0 and 0.06 parallel to the b axis, between 1.6 K and room temperature. The maximum solubility of H in the low-temperature alpha phase was determined to Xmax=0.065+or-0.01 at. H/at. Er. The absorbed hydrogen leads to an increase of the Curie temperatures TC and TC1 and to a decrease of the antiferromagnetic transition temperatures TH and TN, increasing strongly the resistivity jump at TC, Delta rho (TC), as well as the difference Delta rho HN= rho (TH)- rho (TN) in the c axis crystals. It also modifies the superzone effects associated with the sinusoidal and helicoidal spin structures. A quench from room temperature leads to a further increase of TC and TC1, but also to an increase of TH and TN in the hydrogenated crystals. The results are explained by magnetoelastic and electronic interactions of hydrogen in various (ordered and disordered) configurations with the magnetic structures. The thermal variation of rho in the cone-structure region gives evidence for the existence of gap-like behaviour in the spin-wave spectrum; this behaviour can be understood through the overall softness of the whole spectrum and the presence of relatively flat portions in the latter.