Martensitic phase transformation and thickness-dependent magnetization dynamics in off-stoichiometric Co–Fe–Ti–Si Heusler alloy thin films

We report a systematic investigation of the influence of film thickness (25–65 nm) on the martensitic phase transformation (MPT) and the associated magneto-transport and magnetization dynamics of off-stoichiometric Co–Fe–Ti–Si Heusler alloy thin films. Electrical resistivity data reveal a clear first-order martensitic phase transformation in all the films, characterized by thermal hysteresis and a significant drop in temperature-dependent resistivity. The characteristic martensitic transformation temperatures show only a weak dependence on thickness, indicating that MPT is intrinsic to the off-stoichiometric system. Detailed analysis of transport data establishes that the observed resistivity minima at low temperatures result from a competition between electron–phonon scattering and disorder-induced quantum corrections. In the vicinity of MPT, transverse magnetoresistance remains positive and increases sharply from its small magnitude in the martensite phase. Magnetization data confirm that all the films are soft ferromagnetic across the transformation, with very weak magnetic signatures of the transformation. Broadband ferromagnetic resonance reveals that the Gilbert damping constant goes through a minimum (α = 0.0076) for the highest B2-ordered 50 nm film.