Anomalous magnetic viscosity in the bulk amorphous ferromagnets Nd60Fe30Al10 and Nd60Fe20Co10Al10

Abstract

The bulk amorphous ferromagnets Nd60Fe30Al10 and Nd60Fe20Co10Al10 exhibit hard magnetic properties, and time dependent magnetisation measurements have been performed to explore similarities and differences between them. Magnetic viscosity measurements on the major hysteresis loop of Nd60Fe30Al10 are reported, along with data for both alloys showing the behaviour of the irreversible magnetic susceptibility. The fluctuation field, Hf, for each alloy is determined. A focus of the study is investigation of the anomalous magnetic viscosity i.e. non-monotonic behaviour of the time dependent magnetisation (where a peak is observed in the magnetisation), on the recoil curve that leads to the dc demagnetised state. Data showing non-monotonic behaviour in both Nd60Fe30Al10 and Nd60Fe20Co10Al10 is presented. The non-monotonic behaviour is interpreted using the Preisach model, as it predicts a simple functional relationship between the time taken to reach a peak and the applied magnetic field. The experimental data is in good agreement with this simple relationship.