Evaluation of Spin-Current-Induced Permeability Variation toward Time-Varying Magnetic Metamaterials

Abstract

  The permeability (μ) variation of lithographically-prepared magnetic metamaterials consisting of Ta/Py/Pt trilayers is studied by means of spin-torque ferromagnetic resonance (ST-FMR) with a direct current up to ±20 mA. The substrate dependence of ST-FMR signals demonstrate that the non-doped Si substrate is the most stable and capable of carrying large direct currents. The μ analytically calculated on the basis of the experimentally obtained resonance field and Gilbert damping parameter are plotted on a complex plane, which shows the permeability variation visually and quantitatively. The present study enables us to design a microwave converter using time-varying magnetic metamaterials for millimeter wave or terahertz light sources toward the post-5th generation mobile communication system.