Nonlinear Microwave Effects on Iron Based Microstrip Filter

Nonlinear effects in magnetic films are a subject of growing interest. The onset of parametric instability translates into practical power limits for microwave devices. Nearly all high-power studies were done in ferrites; recently, An investigated Permalloy. However, no work has been performed on planar devices or on iron films. Here, we investigate the transmission of cw microwaves in a 6-mm-long, 13-mum-wide and 200-nm-thick iron-based microstrip notch filter in the frequency domain. At a particular field, there are three regions in the transmission response. Up to a threshold power of P_crit, the differential absorption of ferromagnetic resonance (FMR) is nearly constant as a function of input power. Above P_crit, the sample absorption decreases significantly as the power is increased. In addition, we observe a subsidiary absorption (SA) peak at a frequency above that of the FMR. We observed butterfly-like curves (P_crit versus applied static magnetic field H), similar to ferrites, for FMR as well as for the subsidiary absorption. We compare the strength of the critical rf field in Fe, YIG, and Permalloy. These numbers indicate that Fe in a microstrip geometry has a much higher power handling capability. Finally, our structures can also be used as a power limiter. The SA can be significantly increased at high powers, thus limiting the transmission in the frequency range where the SA occurs. The usual FMR peak can be used as a small-signal suppressor