On the theory of multicomponent disordered magnets

The topologically disordered many-component system of magnetic atoms with Heisenberg exchange interaction is investigated with the help of functional integral approach. The partition function for a fixed random configuration of atoms is presented in the form of functional integral over the magnetization fluctuations. Several first coefficients of functional series which represents the free energy functional are calculated. The magnetic part of the free energy for liquid and amorphous states is obtained in the random phase approximation (R.PA). The structure factor of liquid magnet is calculated and its dependence on the magnetic field is analysed for the case of a two-component system. Shift of thermodynamic instability point of liquid under the influence of magnetic field is studied. The Curie temperature of two-sort amorphous magnet is found taking into account the magnetic fluctuations and topological disorder. The explicit expression for the dependence of ferromagnetic ordering temperature on the concentration is calculated for the model with the liquid-type disorder described by the hard sphere structure factor.