Power dependence of electron paramagnetic resonance: Analytical solution of Landau–Lifshitz–Gilbert equation

The solutions of the Landau–Lifshitz–Gilbert (LLG) equation reveal nonlinear effects in electron spin dynamics. Here, the nonmonotonic power dependence of the electron paramagnetic resonance (EPR) signal intensity is derived by solving the LLG equation. The analytical solutions of a spin moment are obtained for linearly polarized microwaves with any power. A tendency of susceptibility from linear to nonlinear is exhibited with increasing microwave power. Both low- and high-power dependences of EPR signal intensity of standard sample 1,3-bisdiphenylene-2-phenylallyl are well explained by the tendency. These findings provide valuable insights into nonlinear behavior of spin dynamics and the quantitative analysis of paramagnetic centers.