Magnetic contribution to the Debye temperature and the lattice heat capacity of ferromagnetic rare-earth metals (using gadolinium as an example)

A thermodynamic approach that describes the spontaneous magnetic contributi on to the Debye temperature of a ferromagnetic metal has been developed usi ng the theory of second-order Landau phase transitions. It is shown that th e essential cause of the formation of the spontaneous magnetic contribution to the Debye temperature is the magnetostrictive variation of the volume. By using an expression for the spontaneous magnetic contribution to the Deb ye temperature, the magneto-phonon contribution to the lattice specific hea t is found. The resulting generalized expression for the Debye temperature is found to be in good agreement with experimental data concerning the elas tic constants of the ferromagnetic phase of gadolinium. The magneto-phonon heat capacity makes an appreciable contribution to the heat-capacity anomal y of gadolinium close to the Curie point. (C) 1999 American Institute of Ph ysics. [S1063-7834(99)02507-1].