Rare-earth-rich metallic glasses. II. Magnetic viscosity

Magnetic viscosity measurements on amorphous ${\mathrm{Tb}}_{75}$ ${\mathrm{Au}}_{25}$ and ${\left({\mathrm{Er}}_{65}{\mathrm{Fe}}_{35}\right)}_{90}$ ${\mathrm{B}}_{10}$ alloys are presented in the temperature range of 1.3 to 30 K. The magnetization in a steady magnetic field is found to follow a logarithmic time dependence for times up to 400 s suggesting a spectrum of activation energies. The magnetic viscosity parameters were used to investigate the temperature dependence of the observed large coercive fields and to study intrinsic temperature and thermal activation effects. It is found that the large change of the coercive field at very low temperatures is mainly due to thermal activation of domains over the energy barriers.