Ferromagnetic resonance imbalance at high microwave power: Effect on the Gilbert damping parameter.

Nowadays, electron spin resonance (ESR) systems are routinely used to measure the ferromagnetic resonance (FMR) in a wide range of experiments. However, the number of spins in ferromagnets far exceeds the small number of spins in paramagnetic systems that ESR systems were originally designed for. In this study, we show that high spin concentration and microwave input power—conditions routinely met in various FMR experiments—lead to the strong distortion of the FMR shape due to the sublinear operating regime of the microwave detector. We introduce the additional imbalance term in the FMR Lorentzian fitting function that allows extracting correct values of the Gilbert damping parameter under such conditions. Our results are crucial for the quantitative estimation of the Gilbert damping—the key parameter in many magnetic and spintronics measurements. [ABSTRACT FROM AUTHOR]