Browsing by Author "Chen, Qi"

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    Giant Spin Hall Effect with Multi-Directional Spin Components in Ni4W
    (2024-11-08) Yang, Yifei; Lee, Seungjun; Chen, Yu-Chia; Chen, Qi; Sousa, Duarte; Odlyzko, Michael; Garcia-Barriocanal, Garcia; Yu, Guichuan; Haugstad, Greg; Fan, Yihong; Huang, Yu-Han; Lyu, Deyuan; Cresswell, Zach; Low, Tony; Wang, Jian-Ping
    Spin-orbit torque (SOT) can be used to efficiently manipulate the magnetic state of magnetic materials, which is an essential element for memory and logic applications. Due to symmetry constraints, only in-plane spins can be injected into the ferromagnet from the underlying SOT layer for conventional SOT materials such as heavy metals and topological materials. Through the use of materials with low symmetries, or other symmetry breaking approaches, unconventional spin currents with out-of-plane polarization has been demonstrated and enabled field-free deterministic switching of perpendicular magnetization. Despite this progress, the SOT efficiency of these materials has typically remained low. Here, we report a giant SOT efficiency of 0.85 in sputtered Ni4W/CoFeB heterostructure at room temperature, as evaluated by second harmonic Hall measurements. In addition, due to the low crystal symmetry of Ni4W, unconventional out-of-plane and Dresselhaus-like spin components were observed. Macro-spin simulation suggests our spin Hall tensor to provide about an order of magnitude improvement in the magnetization switching efficiency, thus broadening the path towards energy efficient spintronic devices using low-symmetry materials.
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    Ramen Spectroscope for Low Temperature Damage during Cell Freezing
    (2015-04-22) Chen, Qi
    The objective of this project is to obtain more details by using confocal Ramen spectroscopy to see the effect of cryoprotectants such as Trehalose, glycerol, ectoine and their mixture on the protection of the cell during freezing and compare with the result from 1XPBS and DMSO. The jurkat cell was used as the sample cell and the test was performed starting from the -6℃ to -50℃ at a moderate cooling rate of 10℃/min. The mixture solution of 5% glecerol, 300mM trehalose and 0.02% ectoine was used as the protection solution. The CRM images were collected at the ultimate temperature (-50℃). Compared with the results achieved from the previous work (1×PBS and 10% DMSO solution). The cryoprotectants mixture presents a better protection effect during the cell freezing. The effect of cryoprotectants mixture at different cooling rates still needs to be studied for the future work.