Lattice Dynamics and Magnetoelastic Coupling in a Frustrated Shape Memory Alloy

Magnetocaloric (MC) materials present an avenue for chemical-free, solid state refrigeration through cooling via adiabatic demagnetization. We have used inelastic neutron scattering to measure the lattice dynamics in the MC shape memory alloy Ni$_{\mathrm{45}}$Co$_{\mathrm{5}}$Mn$_{\mathrm{36.6}}$In$_{\mathrm{13.4}}$. In this presentation, we present the results of inelastic neutron scattering near the Curie temperature. We find that there is an unaccounted-for change in phonon entropy of 0.22 kB atom$^{\mathrm{-1}}$ (26 J kg$^{\mathrm{-1\thinspace }}$K$^{\mathrm{-1}})$, which we attribute to phonon-magnon coupling. We identify an anomalous softening of the TA[100] phonon mode. We also present the results of diffuse neutron and X-ray diffraction experiments and provide an interpretation on the implied local order.