Lattice dynamics across the magnetic transition in (Mn,Fe)1.95(P,Si)

The lattice dynamics in MnFe0.95Si0.50P0.50 were investigated experimentally using Fe57 nuclear inelastic scattering and inelastic x-ray scattering across the first-order magnetic transition which occurs close to room temperature. The lattice dynamics characterization was supported by a macroscopic magnetic characterization, an x-ray diffraction study, and a hyperfine interactions characterization using Mossbauer spectroscopy. The Fe specific and the x-ray generalized density of phonon states were obtained both in the ferromagnetic and in the paramagnetic state. A prominent shift, 2meV at 20meV, in the x-ray generalized density of phonon states across the first-order magnetic transition, that involves vibrations with essentially Fe character, is revealed corroborated by a change in the local environment quantified in the isomer shift and the quadrupole splitting. Above 35meV the vibrational modes are practically insensitive to the magnetic transition. The entropy change induced by a 1T magnetic field across the magnetic transition, ∼10J/K/kg, is only a fraction of the Fe vibrational entropy change, 62(21)J/K/kg.