Effect of Electroplated Ni_1–xFe_xComposition on the Field-Induced Anisotropy

Abstract

Field-induced anisotropy has been proposed as an effective method to produce ferromagnetic rings to produce ferromagnetic rings with radial anisotropy for fluxgate cores.. Compared to stress-induced anisotropy this method easily allows generating a radial anisotropy in electroplated rings. However, it is still not clear what is the source of such anisotropy. It has been suggested that the observed anisotropy could be the effect of magnetocrystalline anisotropy present in the electroplated film because of non-ideal stoichiometry of the alloy. If true this would make impossible to electroplate films with field-induced anisotropy and simultaneously low magnetostriction because this condition occurs at Ni 81 Fe 19 composition where the magnetocrystalline anisotropy vanishes. In order to verify this hypothesis we electroplated several rings changing the composition of the alloy, with and without radial magnetic field applied. It turned out that the field-induced anisotropy was to a large extend independent on the composition of the film and it did not show any vanishing trend as we approach Ni 81 Fe 19 composition. This suggests it is in fact possible to obtain field-induced anisotropy and simultaneously low magnetostriction. Finally we show how such radial field-induced anisotropy reduced the noise of the fluxgate by almost one order of magnitude.