Theoretical study of multiferroic thin films based on a microscopic model

The influence of the surface, film thickness, temperature and ion doping effects on the magnetic and electric properties in multiferroic thin films is studied by a combination of modified Heisenberg and transverse Ising models using a Green's function technique. It is demonstrated that the magnetization M, the polarization P, the critical temperatures T(N) and T(C), the spin-wave energies E(m) and E(e), and their damping are very sensitive to the exchange interaction constants on the surface (A(1s) and J(s)) and in the defect layers (A(1d) and J(d)). It has been found that the damping is enhanced compared to the case with no defect layers. We have obtained that M, P, T(N), T(C) and the spin-wave energies could be increased or decreased by using different kinds of doping ions. The concurrent interaction mechanisms of the magnetic and electric subsystems are shown. The results are in qualitative accordance with the experimental data.