Magnetic viscosity in a UPtAl single crystal

Abstract

UPtAl is a ferromagnet with the Curie temperature 43.5 K, the rectangular hysteresis loop and the coercive force H c=0.7 T at 1.7 K. Due to the strong magnetocrystalline anisotropy, the hysteresis properties are likely caused by the intrinsic coercitivity of narrow domain walls. The magnetic viscosity in UPtAl has been studied by magnetization measurements. In a field slightly lower than H c (by absolute value) the magnetization decreases with time, changes the sign, and tends to saturate in the negative direction. The magnetic relaxation curves measured at different temperatures and fields have been analyzed within the thermal activation mechanism of the movement of narrow domain walls. The thermally activated volume and the expected coercive force for UPtAl without taking into account the thermal fluctuation mechanism have been determined as functions of temperature. The linear size of thermally activated areas was determined to be 1.2 nm at 1.8 K, a value close to the estimated domain walls width.