Magnetic Properties of a UPtAl Single Crystal

Abstract

UPtAl is a ferromagnet with a spontaneous magnetic moment M s =1.38 µ B /f.u. directed along the hexagonal c axis and Curie temperature T C =43.5 K. The uniaxial magnetocrystalline anisotropy is very strong, the estimated anisotropy field B a exceeds 290 T. In a thermally-demagnetized sample the initial susceptibility along the c axis is very low for a wide field interval below a critical field B st . Then the magnetization increases abruptly and saturates in a rather narrow field interval. The low-temperature hysteresis loop is almost rectangular with a 100% remanent magnetization. The coercivity ( B c =0.7 T at 1.7 K) weakens rapidly with increasing temperature and vanishes at 20 K. A zero-field cooled sample exhibits a large thermal hysteresis. In the vicinity of B st and B c , a very pronounced magnetic viscosity is observed. As the main mechanism of the magnetic hysteresis we propose the pinning of domain walls which are very narrow due to the huge anisotropy and a relatively weak exchange interactio...