Nonreciprocal Parametric Magnon Excitation by Surface Mode

Microwave parametric pumping can generate magnons, quanta of magnetization precession dynamics. Here, we show nonreciprocal parametric excitation of magnons, where the magnon oscillation threshold depends on the field direction dependence, in a magnetic thin disk excited by nonuniform microwaves. It is attributed to the excitation of surface mode spin waves, leading to the field switching of magnon excitation.