Electromagnetic Effects in Magnetic Insulators

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Abstract
Electromagnetic modes are capable of strong coupling to magnetostatic modes in magnetic insulators. For certain ranges of magnetic field bias (or, equivalently, sample dimension), the two modes interact and lose their identity. This composite mode has been investigated both experimentally and theoretically. The experiment centered on the modes found in a small YIG sample coupled to an electromagnetic resonator in the form of a rutile disk and on the modes in a large YIG sphere (which forms its own electromagnetic resonator). Coupled-mode theory was applied to the experimental results. The theory has been extended to include the effects of relaxation, nonlinearities, and mode segregation, i.e., the frequency separation of the coupled mode from the allowed frequencies in the low-frequency spinwave manifold (e.g., ferromagnetic or acoustic ferrimagnetic spinwaves). A careful study has been conducted on these segregated modes. Experimental results show that for sufficiently strong coupling the observed mode undergoes a reduction in magnetic loss and a sharp increase in nonlinear threshold, in accordance with the theoretical behavior of a segregated mode.

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