Stress-induced martensitic transformation in epitaxial Ni-Mn-Ga thin films and its correlation to optical and magneto-optical properties
Phys. Rev. B 113, 104420 – Published 12 March, 2026
DOI: https://doi.org/10.1103/b3yr-1yt8
Abstract
The optical and magneto-optical properties of thin epitaxial Ni-Mn-Ga films, with thicknesses ranging from 8 to 160 nm, were investigated across the spectral range of 0.7–6.4 eV. The films were deposited by dc magnetron sputtering on MgO (100) substrates with a stress-mediating Cr buffer layer. Structural and magnetic characterization revealed a stress-induced martensitic transformation for the films thicker than 80 nm, while thinner films remained in an austenite structure due to the substrate constraint. In martensitic samples, a mixture of 14M and NM phases was observed with both X-type and Y-type twin domains. Magneto-optical polar Kerr effect spectra showed a notable evolution with film thicknesses, demonstrating changes in the electronic structure of Ni-Mn-Ga. A combination of spectroscopic ellipsometry and magneto-optical Kerr spectroscopy allowed for the deduction of the spectral dependence of the full permittivity tensor of the investigated samples. Three magneto-optical transitions were fitted to the spectra of nondiagonal permittivity using semiclassical theory, showing strong correlations with in-plane coercivity. Observed correlations highlight the impact of substrate-induced stress on Ni-Mn-Ga films and provide insights into the electronic structure changes associated with the martensitic transformation.
