  The different contributions to the entropy change linked to the
austenite-martensitic transition in a Ni-Mn-Sn metamagnetic shape memory alloy
have been determined by combining different experimental techniques. The
vibrational contribution has been inferred from the vibrational density of
states of both the martensitic and austenite phases. This has been accomplished
by combining time-of-flight neutron scattering measurements and ab-initio
calculations. Further, the electronic part of the entropy change has also been
calculated. Since the martensitic transformation takes place between two
paramagnetic phases, the magnetic contribution can be neglected and the entropy
change can be reduced to the sum of two terms: vibrational and electronic. The
obtained value of the vibrational contribution (-36 \pm 5 J kg^(-1) K^(-1))
nearly provides the total entropy change measured by calorimetry (-41 \pm 3 J
kg^(-1) K^(-1)), the difference being the electronic contribution within the
experimental error.
