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In order to find a microscopic origin of a strong anisotropy, shown by the magnetoresistance in Ca: doped YIG, we investigate a simple system of two hybridizing iron–oxygen clusters with tetrahedral and octahedral symmetries, respectively. By applying a group-theoretical approach to the diagonalization of the Hubbard model with the Zeeman term included, we obtain energy levels and the orbital eigen-states for both the clusters. This is the point of departure for calculating the total probability of the charge transfer between the clusters. And, finally, the magnetoresistance, as a function of the external field, is found at room temperatures. As an origin of the anisotropy in the magnetoresistance, we suggest the symmetry of the orbital eigen-states of the clusters, which finds its reflection in a form of the orbital contribution to the magnetic moments of the clusters.

The effect of oblique co-deposition on magnetic properties of cermet films is studied on a series of (Fe50Co50)x–(Al2O3)1–x granular films with nominal FeCo content x varied at 0.07 < x < 0.49, using FMR. Three observed signals are attributed to local regions differing of compositions, each varying from the nominal x. A microstructure-induced oblique anisotropy has been found above percolation. Its origin may be due to some elongation of grains along a growth direction tilted from the film normal.

The temperature dependence of the spinwave resonance linewidth in thin ferromagnetic metal films has been observed at 35 GHz in the temperature range 4 °K to 300 °K. The data are analyzed in terms of a two-magnon relaxation process induced by a planar inhomogeneity in the internal field of the film. The inhomogeneity is due to imperfections in the film structure introduced during deposition. The linewidth is found to decrease with increasing temperature in a manner similar to the temperature dependence of the magnetization with a mode dependence that is in reasonable agreement with the model proposed.

The behavior of iron in valence states of Fe4 + and Fe2 + has been investigated by measurements of the angular and temperature dependence of the FMR resonance field and linewidth at 9.2 GHz from 4.2 to 295 K on (111) oriented Ca0.142+Fe4+:YIG and Ge0.104 + Fe2 + :YIG epitaxial garnet films. At low temperatures a substantial increase of the first- and second order cubic anisotropy energy has been observed, with K1>0and K2<0 for Fe2 + and K12>0 for Fe4+ containing garnets. However, the magnitude of K1 and K2 is much smaller than predicted. In Ca:YIG a change in sign of dK/dT is observed at T<30 K. Anisotropic FMR linewidth maxima below 50 K for Ca:YIG and Ge:YIG and at 180 K for Ca:YIG have been measured and identified with level splitting and charge transfer processes.

Computer simulations of parametric excitations of spin waves are done in the frame work of the original two modes model (without adding the finite medium correction term). It is shown that hc′, the threshold for auto-oscillations can be less than 0.2 db above hc, the Suhl instability threshold. Moreover, the auto-oscillation is onset with a finite frequency that is smaller than 0.2γ where γ is the spin wave relaxation rate. This result reconciles two of the discrepancies between theory and experiment. The dependence of τd, the time delay in the excitation buildup on the pumping field h exhibits a “critical slowing down” power law: τd=A(h/hc-1)-0.80 over a wide range of h values hc ≪ h ≪ 2.2 hc.

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