Magnon-TA phonon interaction and the specific heat during the premartensitic transformation in ferromagnetic Ni2MnGa

From the basic spin electron-phonon coupling, we deduced the magnon-TA phonon interaction in the Ni2MnGa alloy instead of the magnetoelastic coupling between the magnetization and the amplitude of the TA phonon and suggested that the premartensitic transformation (PT) can be driven by the one-magnon-one-TA phonon interaction. Based on the established interaction Hamiltonian, the specific heat varying with the temperature has been calculated and the specific heat anomaly at the PT temperature has been predicated to make a great contribution to the latent heat during the PT because of the strong magnon-phonon interaction. The PT latent heat has been evaluated to be about 5 J/mol which is in agreement with the experimental results measured [Planes et al. Phys. Rev. Lett. 79 (1997) 3926].