Switching field fluctuation measurement

A specially designed device was developed to measure the switching field fluctuations of bistable microwires with up 30mm in diameter and 17mm in length. It consists of two coaxial coils wounded around a tiny capilar inside which the microwire is inserted. A primary coil 30mm long generates the axial field (41Oe maximum amplitude and 30Hz triangular wave) to excite the magnetisation reversal, and a smaller pick-up 5mm long placed at the middle position of the exciting coil senses that reversal.

The switching field is determined from the induced voltage maximum, actually from the time ts when this occurs, at the ends of the secondary coil during the Barkhausen jump. The distribution of the switching field is obtained by evaluating 1000 consecutive switching processes. The whole set is placed inside a cryostat where temperature is ranged between 77 and 450K.


A similar set-up is used to measure the velocity of the magnetic domain wall propagation along biphase microwires.


The temperature dependence of the wall velocity and the effect of the transverse applied field in the wall velocity are observable in bistable microwires (e.g., Fe base microwire λs ~10-5)


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