Fabrication and FMR studies of ferromagnetic iron-gallium arsenide waveguide structures and application to microwave bandstop filters

Epitaxial growth of magnetic ultrathin films on semiconductor substrate has been attempted for the integration of the magnetic/semiconductor material hybrid devices. Of all the Fe/III-VI semiconductor system, growth of iron film on GaAs (100) has received the most attention due to their smallest lattice mismatch of only 1.4%.; In this dissertation, we report on the growth of high-quality single crystal Fe/Ag multilayer structures on GaAs (100) substrate. The X-ray diffraction (XRD), Magneto-optic Kerr effect (MOKE) and ferromagnetic resonance (FMR) measurements were performed. High quality Ag/Fe multilayer crystalline structures have been grown, as confirmed by read-camera XRD results. We studied the coupling between the electromagnetic signal and the spin excitations in the ultrathin Fe films. In the microwave region this coupling arises when the film magnetization vector M is driven by the magnetic field component of the radiation field. For single crystal Fe films, the corresponding resonance occurs near 10 GHz when no magnetic field is applied. We have observed FMR linewidth broadening on Ag/Fe/Ag/Fe/GaAs samples due to intrinsic damping effect in a frequency range of 10 to 35 GHz. This is a very useful frequency regime for many microwave devices.; Tunable microwave bandstop filters were successfully fabricated using ferromagnetic Fe/Ag/Fe-GaAs and ferromagnetic/antiferromagnetic Cr/Fe/Cr/Fe-GaAs layer structures. The resonant absorption frequency can be tuned electronically by varying the magnitude of external bias magnetic field. This Fe film-based microwave devices possess an important advantage over their Yttrium-Iron-Garnet (YIG)-based counterparts in that for a given operating carrier frequency, it requires a much smaller bias magnetic field than that of YIG devices. This is so because the saturation magnetization of the Fe films is more than one order of magnitude larger than that of YIG. Accordingly, a significantly higher device operating carrier frequency with large electronic tunability could be achieved more readily using the Fe film structures, compared to the previous report on ferromagnetic YIG-based devices.