Antisymmetric contribution to the planar Hall effect ofFe3Sifilms grown onGaAs(113)Asubstrates

Abstract

The planar Hall effect (PHE) in ferromagnets is believed to result from the anisotropic magnetoresistance (AMR) and hence does not change the sign by reversing the direction of the applied in-plane magnetic field. Our studies of the ferromagnetic Heusler alloy ${\mathrm{Fe}}_{3}\mathrm{Si}$ films grown on low-symmetric GaAs(113)A substrates however show a change in the sign of the PHE by reversing the direction of the applied field, indicating the existence of an additional antisymmetric component superimposed with the usual symmetric AMR term. This antisymmetric component shows a maximum along the major in-plane $⟨33\overline{2}⟩$ axes and vanishes along the other major in-plane $⟨\overline{1}10⟩$ axes. A phenomenological model based on the symmetry of the crystal provides a good explanation of the observed antisymmetric contribution to the PHE. The model shows that this component arises from the antisymmetric part of the magnetoresistivity tensor and is basically a second order Hall effect. It is shown that the observed effect can be ascribed to the Umkehr effect, which refers to the coexistence of even and odd terms in the component of magnetoresistivity tensor. A sign reversal of this antisymmetric component is also found for a Si content above 21 at. % and at temperatures below a certain critical temperature which increases with increasing Si content.