GENERATION OF SPIN CURRENT AND MANIPULATION OF MAGNETIC MOMENT IN MAGNETIC THIN FILM HETEROSTRUCTURES

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In this thesis, I summarize my research on the generation of spin current via the spin Hall effect (SHE) in various material systems, the behaviors of the spin-orbit torques (SOTs) which result from the injection of spin current into an adjacent ferromagnet (FM) in the thin film heterostructures under different interfacial and ambient conditions, the engineering of perpendicular magnetic anisotropy (PMA) at the FM/oxide interface, and how to use this effect together with the large SOTs to manipulate the magnetic moment in magnetic tunnel junctions (MTJs). Accordingly, the thesis consists of four sections for the experimental details regarding the above aspects. In the first study, I focused on the behavior of the SOTs generated in normal metal (NM)/FM/oxide heterostructures under different interfacial and ambient conditions. By varying the spin current sources and controlling the different interfaces, the strength of the SOTs can be efficiently modified, pointing out the physical origins and mechanism of the generation and transfer of these SOTs in the NM/FM/oxide heterostructures. In the second study, I explored the SHE in various material systems beyond conventional heavy metals. These material systems include antiferromagnetic alloys and ferromagnetic alloys near the magnetic transition temperatures. By employing spin torque ferromagnetic resonance and the harmonic response technique, I was able to quantify the strength of the SHE in those material systems under both room temperature and low temperature ambient conditions. In the third part, I explained the discovery and manipulation of the PMA at the FM/oxide interface by inserting an ultrathin metallic dusting layer. I demonstrated that with this dusting technique, the PMA can be greatly enhanced and efficiently modified by the types of the dusting material, the amount of that material, and the post-fabrication process involving the dusting layer. In the last part, I showed that by combing the strong SHE in the heavy metal tungsten (W) and the PMA effect from the dusting technique, MTJs with fast, reliable switching and low switching current can be realized in three-terminal nanoscale devices, demonstrating their great potential as a building block for the next generation memory storage elements.

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Date Issued
2018-08-30
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Keywords
spin current; spin-orbit interaction; thin film heterostructure; Applied physics; Spintronics; Physics; Condensed matter physics; Spin Hall Effect; magnetic tunnel junction
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Committee Chair
Buhrman, Robert A.
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Mueller, Erich
Ralph, Daniel C.
Degree Discipline
Physics
Degree Name
Ph. D., Physics
Degree Level
Doctor of Philosophy
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Government Document
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Attribution 4.0 International
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dissertation or thesis
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