Effect of thermal structural instabilities on initial permeability and critical magnetic fields in zeromagnetostrictive amorphous alloys

Abstract

In Metglas 2705MN zeromagnetostrictive amorphous alloy, time effects on the critical magnetic fields for the sudden jump of the ac permeability have been utilized together with the disaccomodation of the initial permeability to investigate structural and magnetic instabilities at different temperatures. Aftereflect phenomena at a given temperature T are reproducible after demagnetization. Time effects on the critical fields are detectable from 200 to 615 K, whilst disaccomodation of the permeability is already negligible at 540 K. Up to 500 K the potential theory for rigid domain wall motion is valid and time instabilities are attributed to local reorientation of mobile defects inside domain walls near free volumes. Beyond 500 K the characteristics of dc hysteresis loops show a drastic increase of local induced anisotropies with increasing T and in these conditions the increasing strength of the domain wall pinning centers seems to favor domain wall bowing.