Barkhausen Volume Research Articles

Magnetic and magneto-optical properties of Tb/Fe multilayers

We report on magnetic and magneto-optical properties of [Tb/Fe] n multilayers. The dependence on Tb and Fe thicknesses and on the stacking parameter n have been studied. For a thick sample ( n=40), we confirm that the ferrimagnetic or compensation temperatures and the magneto-optical effects are close to those deduced previously for Tb x -Fe 1- x metallic alloys having the same nominal composition. Thinner samples ( n<40) exhibit slightly different magnetic properties. In particular, a transition from in-plane to out-of-plane anisotropy for low values of n is evidenced and discussed. Magnetization reversal dynamics are studied and analyzed from magnetic after-effect measurements and microscopic domain imaging. Typical values of Barkhausen volumes are deduced.

Temperature effects on domain wall dynamics in ultrathin ferromagnetic films

Thermally activated domain wall dynamics in ultrathin Au/Co/Au films with perpendicular anisotropy are studied at different temperatures. Barkhausen volumes and activation energies of the samples are derived. The origin of the coercive field is briefly discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Power losses in a conducting sheet with bar domains. I. Eddy currents due to Barkhausen regions

Energy loss in magnetic steels is generally taken to consist of two parts: static loss, associated with Barkhausen switching and assumed independent of drive frequency, and eddy current loss due to wall motion. Little effort has gone into analyzing the Barkhausen contribution. We consider a model of a magnetic sample in which the Barkhausen volumes are represented as a distribution of sites which reverse their moments at a uniform rate and only along a single axis. Using Green’s function the current distribution of symmetrically placed regions is determined subject to the boundary conditions of periodic bar domains in a thin sheet. In subsequent reports this is used to calculate losses.

Barkhausen noise of 3% Si-Fe strips after plastic deformation

Grain-oriented 3% Si-Fe strips were plastically strained up to \epsilon = 3 %. The frequency spectrum E(f) of the Barkhausen noise was measured. From E(O) a mean Barkhausen volume v eff is calculated. The noise and v eff are diminished after plastic deformation mainly already in the region \epsilon %, where the coercive field remains still constant, v eff is related to a mean irreversible susceptibility, which is mainly determined by the hysteresis loop. By measurements of the correlation of the flux changes along the specimen a mean length of the Barkhausen volumes was obtained. Its diminution mainly causes the diminution of v eff . The connection of the results with changes of the domain and dislocation structure is discussed.