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Ferromagnetic Resonance and Spin Hall Torque for Nanometric Thick Magnetic Insulator |Normal Metal Bilayers System


In bilayer system, consists of ferromagnetic insulator, high spin orbit coupling normal metal (FM|NM), a new ferromagnetic resonance (FMR) damping that depends on varying the thickness of the normal metal observed. This new enhancement in the damping attributed to magnetic proximity effect (MPE) at the interface, which is verified by the increases in the real part of spin mixing conductance.

Spin pumping phenomena occurs when pure spin current can flow into the normal metal when the ferromagnetic film is at precession in bilayer system. The Onsager reciprocity implies that there must be a transfer of spin angular momentum from the normal metal to the magnetization of the magnetic layer. This effect is called; spin Hall torque ferromagnetic resonance (SHT-FMR). The combination of spin Hall effect and spin transfer torque allows the manipulations of spin wave damping and anti-damping by applying DC current at specific orientation to the DC field. In epitaxial nanometric thick yttrium iron garnet films (YIG) grown on gadolinium gallium garnet (GGG) substrates via pulsed laser deposition the SHT-FMR is extremely very low Js &sim 1066 A/m^2 . This value can not be explained by existence theory. The joule heating effect on the current induced SHT-FMR verified by temperature dependence FMR. The DC generated Oersted field evaluated by VSM. Power dependence on the FMR under varying the thickness might exhibit different critical thickness compare to the thickness where the enhancement of damping do saturate. Out of plane, FMR angular dependence was carried out to study extrinsic and intrinsic damping.

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