Instability of Magnetic Resonance in Single Crystal Spheres of Yttrium Iron Garnet

Abstract

Instabilities in YIG spheres that exist above certain threshold power values of cw microwave field are studied using samples of about 14−12 mm diam, that have low power line widths of 1 oe or less. Whereas the characteristic behavior such as asymmetrical line shape, “jump” effect etc. is somewhat similar to that reported for disks, the phenomenon is generally different. It has been determined that this instability, which can occur at cw power levels below the threshold for significant spin wave growth, is due entirely to the heating effect of resonance absorption upon the anisotropy energy of the crystal lattice. As a result, the instability is characterized by a threshold curve that follows both the extrema and symmetry of the anisotropy curve for a given orientation. A straightforward theoretical explanation based on familiar relationships is outlined which fits the instability threshold vsorientation curve. The temperature instability provides a technique for measuring the “g” factor that is believed to be more direct than previous methods.

Electrical detection of magnetization dynamics via spin rectification effects

“…The onset of the foldover and bistability effects also occur in magnetic systems when the resonance shift reaches a critical value which was initially investigated by Anderson and Suhl [322]. However in the experimental search for foldover effects in magnetic systems, large discrepancies from the Anderson-Suhl model have been found [324][325][326][327][328][329][330][331][332][333][334][335][336]. These discrepancies were partially due to the presence of spin wave instabilities and thermal effects, which made the interpretation of early experiments difficult, but the primary reason that the critical frequency shift could not be reached is due to the effect of nonlinear damping, which effectively pushes the power and frequency required to observe foldover effects beyond the range initially investigated.…”

Nonlinear ferromagnetic resonance and foldover in yttrium iron garnet thin films-inadequacy of the classical model

“…The frequency may be written as (6) where is a power response coefficient. In the limit of very low power, one may ignore the frequency shift term in (6). The main mode frequency then goes over to and (5) becomes a simple Lorentzian.…”

“…4 and 5. One may also use (5) and (6) to evaluate frequency jump points for up-sweep and down-sweep frequency traces at fixed power or power jump points for increasing and decreasing power traces at fixed frequency. Such calculated profiles and jump points provide a quantitative way to compare theory with experiment, since the jump points may be measured explicitly from data of the sort shown in Figs.…”

“…In terms of these new parameters, the nonlinear FMR response based on (5) and (6) takes the form of a cubic equation given by (11) For any given field and input power level, the roots for as a function of frequency define the resonance response. Formally, the transition from a single valued absorption to a foldover response is related to the change in the number of unequal real roots to (11) from one to three.…”

Ferrimagnetic Oscillator Magnetometer

“…Although calculating the value of this term for the general case of an arbitrary-direction magnetic field is somewhat involved [129], the calculation simplifies for external magnetic fields confined to lie in the {110} plane. Under these conditions, the uniform mode resonant frequency differs from ω y = γB and is instead given to good approximation by [130][131][132]…”