Lattice vibrations boost demagnetization entropy in a shape-memory alloy
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2015 American Physical Society. 2015 American Physical Society. 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 material Ni45Co5Mn36.6In13.4. Upon heating across the Curie temperature (TC), the material exhibits an anomalous increase in phonon entropy of 0.220.04kB/atom, which is ten times larger than expected from conventional thermal expansion. This transition is accompanied by an abrupt softening of the transverse optic phonon. We present first-principles calculations showing a strong coupling between lattice distortions and magnetic excitations.