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(a) Setup for measuring the hysteresis curves with an applied rf-field. (b) Contour plot of the coercive field as functions of rf field and frequency. The coercive field is strongly reduced at microwave frequencies in the region around 2 GHz and decreases as the microwave field amplitude increases.
(a) Hysteresis curves with and without an applied microwave field of 0.4 mT and a frequency of 2.15 GHz. Application of the microwave field reduces the coercive field. The inset shows simulated hysteresis curves for a array with (open red circles) and without (full black squares) an applied microwave field of 0.4 mT and a frequency of 2.15 GHz. (b) FMR frequency vs applied magnetic field. The curve for increasing applied field (red triangles) was obtained by inverting the measured curve for decreasing applied field (black circles). The sample was saturated with a positive magnetic field prior to each measurement. The inset shows a resonance curve for an applied field of 4.7 mT. The vertical dashed lines in (a) and (b) indicate the fields at which reversal begins and ends for an rf field of 0.4 mT. (c) Dependence of the coercive (red squares) and the nucleation (black circles) field on the amplitude of the rf field for a frequency of 2.15 GHz.
The coercive field vs microwave frequency is shown for micromagnetic simulations for a single magnetic element (a) and for the dipole approximation of a nanodot array (b). The microwave amplitudes were, respectively, 0.3 and 0.35 mT.
The coercive field was determined by simulating the magnetic reversal of a nanodot array with an applied microwave field for varying frequency and amplitude.
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