Discrimination of vibrational modes in Ni2MnGa thin films

Abstract

Vibrational properties in magnetic shape memory alloys are intrinsically connected to the topologies formed due to temperature-dependent breakdown of symmetry. In this sense, herein, we apply Raman spectroscopy in the study of Ni2MnGa films prepared by sputtering on glass and gallium arsenide substrates. Different laser wavelengths probe the Raman active vibrational modes. The non-equilibrium heating mechanisms of the electronic lattice induced by excitation laser power within the thermal penetration depth are used to explain the formation of higher order vibrational modes resulting from phonon-assisted intra-band electronic excitations. The discrimination of the Raman active modes is performed based on calculations carried out within the framework of the density functional theory considering the coexistence of austenite and martensite phases as a function of temperature in films with different crystalline textures and residual stresses. More importantly, this work presents a simple way to discriminate the vibrational modes of the austenite and martensite phases in Ni2MnGa thin films that can be easily applied in the nanodevice development process.