Figure 1: Illustration of the operation principle of the N-FMR device.
From: Adaptive microwave impedance memory effect in a ferromagnetic insulator
(a,b) Illustration of the experimental setup (a) and the magnetic microwave near field structure (H-MWNF; b) simulated at 1.0 GHz (COMSOL Multiphysics). The stepped impedance low pass filter (SILPF) consists of a cascade of low impedance lines (LIL) alternately connected with high impedance lines (HIL), where the H-MWNF distribution of the SILPF is localized around the HILs. The yttrium iron garnet (YIG) thin film grown on GGG (111) substrate is placed on the HIL of the SILPF, and thus, it interacts with the H-MWNF of the SILPF. Two axes are defined according to the magneto optical Kerr effects (MOKE): longitudinal and transverse MOKE effect for the LO-axis and the TR-axis, respectively, and the polarization direction of the H-MWNF is parallel to the LO-axis. (c) Equivalent circuit model for the ferromagnetic resonance (FMR) device, where the impedance change (Zs) of the device by the YIG is described by a variable inductor (ΔL) connected in series with the waveguide system (Z0). (d) Illustration of the FMR effect: the magnetic moment under a static magnetic field (Hstatic) precess by the microwave magnetic field (Hrf), where the polarization directions of the Hstatic and Hrf are perpendicular to each other. The change of inductance of the device is a function of magnetic susceptibility (χ) of the YIG for the Hrf, where the χ is determined by the FMR frequency (ωr) that depends on the Hstatic. (e,f) Illustrations for the change of microwave transmittance response by the FMR frequency shift. When the FMR frequency increases from f1 to f2, the imaginary part of the χ (χ′′) at f1 is decreased by the FMR frequency shift, and as a result, the transmitted microwave intensity at f1 is increased by a decrease of FMR absorption that is a function of χ′′. (g) Illustrations on the operation principle of the N-FMR device for the probing and the modulation process.
