Nucleation in first-order phase transitions in magnetic materials
Abstract
The problem of inhomogeneous states of magnets in the neighborhood of the temperature of a first-order phase transition is considered. Besides the magnetic parameters of the system, the interatomic spacings of the crystal lattice also vary at such a phase transition; hence, the magnetoelastic and elastic energies are taken into account in the thermodynamics of the system. The structure and energy of the interphase transition layer are found. It is shown that the paramagnet-antiferromagnet transitions are accompanied by the appearance of spherical nuclei; estimates are carried out of the nucleation parameters as a result of quantum tunneling. It is shown that the interdomain boundary of an uniaxial ferromagnet is converted into a paramagnetic nucleus at the equilibrium temperature for the ferromagnet-paramagnet transition and an intermediate domain structure of alternating ferromagnetic and paramagnetic phases can exist at this temperature. The paramagnet-ferromagnet and antiferromagnet- ferrimagnet transitions are accompanied by the appearance of nuclei of spherical or extended (along the magnetization) shape. The shape and size of the critical nuclei are determined.