Pumping-field-induced dynamic effects in micron-sized permalloy lines and their influence on HF filter applications

We present a combined time- and frequency-domain study on the dynamic properties of 2-μm-wide Permalloy (Py) lines with different shape anisotropies placed on top of coplanar waveguides. The observed results are compared to numerical simulations of the magnetization dynamics using a macrospin model. For small-angle excitation, the inductive measurement of the resonance frequency in the frequency domain is equal to that in the time domain. However, if high pumping field amplitudes are used in the time-domain measurements, additional effects appear that shift the resonance frequency. They are caused by the large precession angle of the magnetization and the tilting of the equilibrium angle of the magnetization due to the presence of the pumping field. Depending on whether the shape anisotropy of the Py line is larger or smaller than the pumping field, the direction of this shift is either to low or to high frequencies. The simulations qualitatively confirm these experimental observations.