Application of a Microfabricated Microwave Resonator in a Co - Pd –Based Magnetic Hydrogen-Gas Sensor

We investigate the ferromagnetic resonance (FMR) response of microfabricated microwave resonators loaded with small Co₁₆Pd₈₄ alloy rectangles. A major increase in the FMR signal-to-noise ratio is achieved by employing the microwave-resonator structure. A FMR peak shift similar to that of Co₁₆Pd₈₄ continuous films is measured in the presence of hydrogen gas in the sample environment. We show that the very high sensitivity of the FMR signal of the Co₁₆Pd₈₄ alloy rectangle to hydrogen exposure can be used to measure relatively small hydrogen-concentration steps near 100% H₂. Additionally, we also demonstrate that this structure can measure hydrogen over a concentration range from 3% to 100% H₂ in N₂. In time-dependent FMR measurements, we discover a temperature dependence of the FMR signal, which we relate to intrinsic temperature-dependent changes in saturation magnetization and the magnetic anisotropy of the Co-Pd alloy.