Selective electronic excitations in nearly half-metallic Heusler alloy NiFeMnSn - A Raman spectroscopic study

Abstract

Half-metallic ferromagnetic full Heusler alloy NiFeMnSn is a promising material in spintronic device fabrication as it carries high spin polarization and high Curie temperature (Tc = 405 K). Understanding electronic excitations in a spin-polarized band structure is essential for the further use of this material in spin-based devices and to optimize the spin-dependent electronic structure in related compounds. In this Letter, we report electronic Raman scattering of NiFeMnSn with spectral signatures at a higher wavenumber than expected from the calculated phonon modes of the system. Temperature-dependent Raman spectroscopy demonstrates a non-monotonic behavior of the Raman shift with temperature across Tc. The orbital resolved electronic density of states and electronic band structure for both spin channels of the system, as obtained from the first principles density functional theory calculations, suggest that the observed Raman signatures originate from the Fe d orbital and its splitting due to the crystal field near the Fermi level. Furthermore, a strong magnetic field dependence of the spectral profile is observed. The study not only exhibits electronic Raman scattering in a Heusler alloy compound, which was unexplored to date, but also establishes Raman scattering as a promising probe to study the orbital-resolved partial density of states in the band structure near the Fermi level of a Heusler alloy.