Millimeter wave ferromagnetic resonance in gallium-substituted ε-iron oxide

摘要

In millimeter wave frequency range, hexagonal ferrites with high uniaxial anisotropic magnetic fields are used as absorbers. These ferrites include M-type barium ferrite (BaFe_(12)O_(19)) and strontium ferrite (SrFe_(12)O_(19)), which have natural ferromagnetic resonant frequency range from 40 GHz to 60 GHz. However, the higher frequency range lacks suitable materials that support the higher frequency ferromagnetic resonance. A new series of gallium-substituted e-iron oxides (ε-Ga_xFe_(2-x)O_3) are synthesized which have ferromagnetic resonant frequencies appearing over the frequency range 30 GHz-150 GHz. The ε-Ga_xFe_(2-x)O_3 is synthesized by the combination of reverse micelle and sol-gel techniques or the sol-gel method only. The particle sizes are observed to be smaller than 100 nm. In this paper, the free space magneto-optical approach has been employed to study these newly developed ε-Ga_xFe_(2-x)O_3 particles in millimeter waves. This technique enables to obtain precise transmission spectra to determine the dielectric and magnetic properties of both isotropic and anisotropic ferrites in the millimeter wave frequency range from a single set of direct measurements. The transmittance and absorbance spectra of ε-Ga_xFe_(2-x)O_3 are shown in this paper. Strong ferromagnetic resonances at different frequencies determined by the x parameter are found.