Magnetoelectric properties of LiCoPO4: microscopic theory

The microscopic description of the magnetoelectric effect in LiCoPO4 is giv en. The "one-ion" approximation in which the magnetic order is presented by a Weiss molecular field approximation is taken as the basis of the model. Using the lowest possible order of perturbation theory the mechanism analog ous to that of the changes due to an electric field of g-factor rather than a mechanism which involves changes of the quadratic axial term ("D term") in the spin-Hamiltonian is considered. Within the framework of the model it is shown that the odd part of the crystalline electric field and operator of the electric dipole transition can be represented by an effective operat or with even parity that allows us a priori to take into account a parity s election rule. The expressions for the magnetoelectric tensor have been obt ained, The theory may be applicable not only to the description of the stat ic ME response but also to the description of the response of the system at optical frequencies. (C) 1999 Elsevier Science B.V. All rights reserved.