Effective temperature, thermodynamical functions, and equilibrium properties of excited domain structure

The theory of the equilibrium properties of stripe domain structure (DS) of nonhomogeneous magnets, induced by a variable magnetic field, is developed. It is shown that an induced DS is a thermodynamic system characterized by an effective temperature which may be many orders of magnitude higher than the room temperature. For a DS of this kind, the thermodynamic functions are derived and the equilibrium conditions are determined. It is found that the entropy term in the free energy function is responsible for DS fragmentation under the variable field action, for the hysteretic dependence of the DS period on the frequency and the amplitude of the variable field, and for phase transitions attended with a jump in the number of domains. (C) 2000 MAIK "Nauka/Interperiodica".