Magneto-Optical Spectroscopy of Heusler Alloys: Bulk Samples, Thin Films and Microwires

Abstract

We report magneto-optical spectra of the Heusler bulk alloys Ni-Mn-In, thin films Ni-Mn-Ga, microwires Ni-Mn-In and Ni-Mn-Ga in martensitic and austenitic states. Transversal Kerr effect (TKE) was studied at an angle of light incidence of 68° with respect to the sample plane, in the energy range 0.5 eV < E < 4.0 eV, at 50 350 K temperatures, and in magnetic fields up to 3.5 kOe. The TKE spectra profile does not change too much at martensitic transformation in Ni2MnGa thin films, only magnitudes of characteristic maxima decrease. The magneto-optical response of Ni2MnGa microwires is very similar to that for Ni2MnGa thin films. For most of studied bulk samples, the TKE signal is very weak (about 10-5), about two orders of magnitude smaller than for thin films, and in many cases could not be detected at all. It indicates the strong dependence of the magneto-optical response of Heusler alloys on the quality of optically or electrochemically polished surfaces and their microstructure.