Dynamics and relaxation of large Barkhausen discontinuity in amorphous wires

Domain wall processes (domain wall configuration, propagation, and collapse) in magnetostrictive amorphous wires of the composition Fe_77.5Si_7.5B₁₅ were investigated. The wires were held under tensile stress (up to 1700 MPa in the case of as-quenched). The domain wall length and normal mobility (or damping) as functions of applied stress were found experimentally and from an ellipsoidal domain model. This allows the losses to be separated into eddy current and spin relaxation contributions. It was demonstrated that the spin relaxation contribution to the total damping parameter becomes dominant with increase of tension and leads to a dramatic decrease of the wall mobility. This is the reason cold-drawn and then tension-heated wires with high residual stress exhibit a much lower mobility in spite of the smaller diameter. The process of domain collapse at a collision of two domain walls is accompanied by a very sharp voltage pulse. It is shown that during the collapse the domain is affected by a growing internal magnetic field connected with an excess of domain surface energy in comparison with magnetostatic energy