Direct measurement of nonlinear ferromagnetic damping via the intrinsic foldover effect

An approach to measure precisely nonlinear ferromagnetic damping is demonstrated by using spin dynamos in combination with sensitive electrical probing techniques. The directly measured intrinsic foldover effect unravels a 50-year-old mystery of ferromagnetic metals. Pivotal importance of nonlinear ferromagnetic damping is uncovered via its distinct dependence on the frequency, amplitude, and initial conditions. The experimental results are in excellent agreement with a nonlinear oscillator model, which revises the pioneer work of Anderson and Suhl for nonlinear magnetization dynamics.