The spin-fluctuation theory of magnetism is generalized for magnets of a complex crystal and magnetic structure. An expression for free energy itinerant p, d-electrons described by the Hubbard Hamiltonian is obtained with allowance for static displacements of ionic cores which result in changes of the lattice symmetry. The approximation of uniform local fields is used to calculate free energy. The developed approach is applied to study the competition of magnetic and structural order parameters in ferromagnetic MnAs at T = 0. It is shown that the original structural distortions of the initial nickel-arsenide lattice (the nonzero structural-order parameter) cause the average energy of itinerant electrons to decrease. The distortions can be stabilized due to the competition between electronic energy and energy of ion-ion interaction of the crystal. The interaction of structural and magnetic order parameters is responsible for the suppression of structure distortions. It is shown that the magnetization (spontaneous or magnetic field induced) occurred in the system may result in the restoration of the initial nickel-arsenide structure. A similar magnetostructural transition is observed experimentally.

Індекс рубрикатора НБУВ: В379.251

Рубрики:

Фазові рівноваги. Фазові перетворення

Шифр НБУВ: Ж14063 Пошук видання у каталогах НБУВ 

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