engleski

Magnetization processes in metallic glasses

The measurements on amorphous ferromagnetic ribbons have shown that direct (JD) and alternating (JA) core-current can affect the M-H loop and cause effects like decrease the coercive field Hc (hence decrease hysteresis loss E), shift the center of the M-H loop (C) along the H-axis, and change the permeability, maximum (Mm) and remanent (Mr) magnetization of the sample. These effects are associated with transverse field Hp generated by JD (static Hp). The magnitude of Hp increases linearly with the distance from the center of the ribbon and reaches the maximum at its surface, hence the term “surface field”. In order to explain the observed effects and to better understand the magnetization processes in these samples, a simple phenomenological model for the influence of surface fields Hp on the magnetization of the sample has been developed. For the coercive field, the model predicts linearly decreasing Hc with Hp (at not too small Hp). The measurements of Hc vs. Hp for a number of amorphous ferromagnetic ribbons (both magnetostrictive and nonmagnetostrictive) agree well with the model prediction for moderate values of static Hp, whereas, at elevated Hps, Hc tends to saturation. Furthermore, in very soft amorphous ferromagnetic ribbons surface pinning of domain walls leads to deviation in behavior of Hc from that predicted by simple model on all values of Hc and for all Hp (static and dynamic). The observed deviations from the model predictions motivated us to revise the model taking into account the complex domain structure of a real sample and the influence of the high surface field on this structure. In addition to the description of the 'unusual' influence of Hp (both static and dynamic) on the M- H loops and their parameters for nanocrystalline FeCuNbSiB ribbon we also present here an improved model, which fully accounts for the observed phenomena.

metallic glasses ; magnetization ; ferromagnetic ribbons

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