| Summary: | 碩士 === 國立臺灣大學 === 材料科學與工程學研究所 === 107 === Spin-orbit torque magnetoresistive random access memory (SOT-MRAM) is a promising memory device. Its basic structure is composed of two major parts, spin-Hall induced layer and magnetic layer. For spin-Hall materials, heavy transition metals with large atomic numbers are the most popular candidates due to their large spin-Hall ratios. As for magnetic layers, materials with perpendicular magnetic anisotropy (PMA) is our priority since this property can provide higher memory density and thermal stability for MRAM devices. Thus my investigation focuses on the comparative study on spin-orbit torque efficiencies from different magnetic heterostructures with PMA.
In my investigation, W is chosen for its largest spin-Hall ratio among all heavy transition metals, which makes it a good candidate for generating efficient damping-like spin-orbit torque (DL-SOT) acting upon adjacent ferromagnetic or ferrimagnetic layer. Here I provide a systematic study on the spin transport properties of W/FM magnetic heterostructures with the FM layer being ferromagnetic or ferrimagnetic with PMA. The DL-SOT efficiency , which is characterized by a current-induced hysteresis loop shift method, is found to be correlated to the microstructure of W buffer layer in both W/ and W/ systems. Maximum values of and are achieved when the W layer is amorphous in the W/ and W/ heterostructures, respectively. Our results suggest that the spin-Hall effect from resistive phase of W can be utilized to effectively control both ferromagnetic and ferrimagnetic layers through a DL-SOT mechanism.
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