Thermal relaxation of magnetic clusters in amorphous Hf(57)Fe(43) alloy.

The magnetization processes in binary magnetic/non-magnetic amorphous alloy Hf(57)Fe(43) are investigated by the detailed measurement of magnetic hysteresis loops, temperature dependence of magnetization, relaxation of magnetization and magnetic ac susceptibility, including a nonlinear term. Blocking of magnetic moments at lower temperatures is accompanied by the slow relaxation of magnetization and magnetic hysteresis loops. All of the observed properties are explained by the superparamagnetic behaviour of the single domain magnetic clusters inside the non-magnetic host, their blocking by the anisotropy barriers and thermal fluctuation over the barriers accompanied by relaxation of magnetization. From magnetic viscosity analysis based on thermal relaxation over the anisotropy barriers it is found that magnetic clusters occupy the characteristic volume from 25 up to 200 nm(3). The validity of the superparamagnetic model of Hf(57)Fe(43) is based on the concentration of iron in the Hf(100-x)Fe(x) system that is just below the threshold for long range magnetic ordering. This work also throws more light on the magnetic behaviour of other amorphous alloys.