A comparative study has been carried out on the magnetic properties of the Heisenberg-like models with and without internal spin fluctuations. A two-spins-per-site Heisenberg-like model is used to mimic the internal spin fluctuations inside atoms. Using the double-time Green's function decoupling method, we have calculated the magnetization and paramagnetic susceptibility of the model Hamiltonians for different atomic spins as functions of the temperature and exchange energies. Our study suggests that the internal spin fluctuations generally reduce the transition temperature, and modify the magnetic behaviours. Unlike the results obtained by using the usual Heisenberg model, our results show that the Curie constant of the two-spins-per-site Heisenberg model depends on the individual moments, rather than on the resultant saturated magnetic moment. The possible physical implication of our result is also discussed.
Based on the extended s-d exchange model, which includes both isotropic and anisotropic spin interactions between conduction electrons and local states, we have derived analytically the interlayer coupling across a semiconductor spacer with a general band structure. Both Heisenberg-type and Dzyaloshinski-Moriya ͑DM͒ -type Ruderman-Kittel-Kasuya-Yosida-like interlayer coupling are obtained as a result of spin-orbit interaction. The interlayer coupling decreases exponentially with spacer thickness and the oscillation period depends on the band structure and orientation of spacers. Our result is different from previous theory; in particular, the DM-type interlayer exchange coupling offers a natural explanation to the noncollinear alignment of neighboring ferromagnetic layers as were observed in recent experiments on magnetic-semiconductor multilayer structures.
The magneto-optical polar Kerr rotation spectra and reflectivity spectra in the wavelength region 400–700 nm are studied for Fe/PbTe and Fe/Pb bilayer films. Large Kerr rotation enhancement with high reflectivity was observed. The experimental data of reflectivity are nearly consistent with theoretical calculation using Fresnel’s equations. However, the observed Kerr rotation spectra behavior is quite different from that expected by macroscopic optical theory.
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