Ta thickness effect on field-free switching and spin-orbit torque efficiency in a ferromagnetically coupled Co/Ta/CoFeB trilayer

Current induced spin-orbit torque(SOT)switching of magnetization is a promising technology for nonvolatile spintronic memory and logic applications.In this work,we systematically investigated the effect of Ta thickness on the magnetic properties,field-free switching and SOT efficiency in a ferromagnetically coupled Co/Ta/Co Fe B trilayer with perpendicular magnetic anisotropy.We found that both the anisotropy field and coercivity increase with increasing Ta thickness from0.15 nm to 0.4 nm.With further increase of Ta thickness to 0.5 nm,two-step switching is observed,indicating that the two magnetic layers are magnetically decoupled.Measurements of pulse-current induced magnetization switching and harmonic Hall voltages show that the critical switching current density increases while the field-free switching ratio and SOT efficiency decrease with increasing Ta thickness.Both the enhanced spin memory loss and reduced interlayer exchange coupling might be responsible for theβ_(DL)decrease as the Ta spacer thickness increases.The studied structure with the incorporation of a Co Fe B layer is able to realize field-free switching in the strong ferromagnetic coupling region,which may contribute to the further development of magnetic tunnel junctions for better memory applications.

脑血管狭窄行神经血管介入术后不良事件与抗血小板药物抵抗的相关性研究

目的探讨脑血管狭窄行神经血管介入术后不良事件与抗血小板药物抵抗的相关性。方法选取温州市中西结合医院2020年1-12月行神经血管介入治疗的脑血管狭窄患者148例为研究对象,记录患者抗血小板药物治疗前及治疗后24 h血小板功能,分析抗血小板药物抵抗情况;于神经血管介入术后3个月、6个月、1年通过随访的方式记录患者不良事件,采用病例对照研究方法,根据患者是否发生不良事件分为发生组和未发生组,采用Spearman相关系数分析神经血管介入术后不良事件与抗血小板药物抵抗的相关性。结果148例患者随访1年,29例失访,最终纳入119例患者,其中41例发生不良事件,未发生不良事件78例。发生组用药前血小板膜糖蛋白P-选择素、血小板活化复合物表达水平分别为(20.22±6.33)%、(68.80±11.52)%,用药后分别为(15.77±4.12)%、(43.19±5.90)%,均高于未发生组[用药前:(16.85±3.24)%、(62.34±10.77)%,用药后:(8.31±2.97)%、(35.85±5.14)%](用药前:t=3.20、2.97,均P<0.05;用药后:t=10.28、6.74,均P<0.05)。发生组阿司匹林抵抗、氯吡格雷抵抗发生率分别为51.2%(21/41)、43.9%(20/41),均高于未发生组的26.9%(8/78)、19.2%(9/78)(χ^(2)=24.47、20.23,均P<0.001)。Spearman相关性分析显示,阿司匹林抵抗、氯吡格雷抵抗均与神经血管介入术后不良事件发生呈中等强度正相关(r=0.45、0.41,均P<0.05)。结论脑血管狭窄神经血管介入术后不良事件与抗血小板药物阿司匹林、氯吡格雷抵抗均呈中等强度正相关。

Field-free switching through bulk spin−orbit torque in L10-FePt films deposited on vicinal substrates

L1_(0)-FePt distinguishes itself for its ultrahigh perpendicular magnetic anisotropy(PMA),enabling thermally stabile memory cells to scale down to 3 nm.The recently discovered“bulk”spin−orbit torques in L1_(0)-FePt provide an efficient and scalable way to manipulate the L1_(0)-FePt magnetization.However,the existence of an external field during the switching limits its practical application,and therefore field-free switching of L1_(0)-FePt is highly demanded.In this manuscript,by growing the L1_(0)-FePt film on vicinal MgO(001)substrates,we realize the field-free switching of L1_(0)-FePt.This method is different from previously established strategies as it does not need to add other functional layers or create asymmetry in the film structure.The dependence on the vicinal angle,film thickness,and growth temperature demonstrates a wide operation window for the fieldfree switching of L1_(0)-FePt.We confirm the physical origin of the field-free switching is due to the tilted anisotropy of L1_(0)-FePt induced by the vicinal surface.We also quantitatively characterize the spin-orbit torques in the L1_(0)-FePt films.Our results extend beyond the established strategies to realize field-free switching,and potentially could be applied to mass production.