The dynamical susceptibility and finite temperature collective excitations in monolayer spin film are calculated using the anisotropic exchange XZ-Heisenberg model for different spin magnitude and the functional integral method. Combining mean field and Gaussian approximation, it is shown that the internal transverse field induced by internal transverse exchange interaction, leads to a decrease (increase) of the spin wave energy in the temperature region below (above) the spin reorientation temperature. This temperature is of the same nature as the critical temperature of the transverse Ising model studied previously. Reduction of the external spin reorientation transverse field (the critical tuning parameter) by intrinsic transverse exchange is demonstrated.
The Ising spin model with random competing ferromagnetic, antiferromagnetic exchange interactions in the external field is used to investigate the First Order Magnetization Process at low temperature in doped polycrystalline magnetic perovskite Pr 0.5 Ca 0.5 Mn 1¹x M x O 3 (M = Co, Ga). Using Callen identity in the correlated effective field approximation, our calculation describes well the experimental behavior, which is explained by the reorientation of antiferromagnetic clusters and by the expansion of ferromagnetic clusters in the external field at low temperature. The origin of the number of critical fields at which the steps of magnetization occurred, the magnitude of these steps and the related jumps in the magnetic field dependent resistivity are also discussed.
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