Cui Baoshan, Zhu Zengtai, Wu Chuangwen, Guo Xiaobin, Nie Zhuyang, Wu Hao, Guo Tengyu, Chen Peng, Zheng Dongfeng, Yu Tian, Xi Li, Zeng Zhongming, Liang Shiheng, Zhang Guangyu, Yu Guoqiang, Wang Kang L
Songshan Lake Materials Laboratory, Dongguan 523808, China.
Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
Nanomaterials (Basel). 2022 May 31;12(11):1887. doi: 10.3390/nano12111887.
The spin-orbit torques (SOTs) in the heavy metal (HM)/ferromagnetic metal (FM) structure hold promise for next-generation low-power and high-density spintronic memory and logic applications. For the SOT switching of a perpendicular magnetization, an external magnetic field is inevitable for breaking the mirror symmetry, which is not practical for high-density nanoelectronics applications. In this work, we study the current-induced field-free SOT switching and SOT perpendicular effective field (Hzeff) in a variety of laterally asymmetric multilayers, where the asymmetry is introduced by growing the FM layer in a wedge shape. We show that the design of structural asymmetry by wedging the FM layer is a universal scheme for realizing field-free SOT switching. Moreover, by comparing the FM layer thickness dependence of (Hzeff) in different samples, we show that the efficiency (Hzeff/, is the current density) is sensitive to the HM/FM interface and the FM layer thickness. The sign of for thin FM thicknesses is related to the spin Hall angle () of the HM layer attached to the FM layer. changes its sign with the thickness of the FM layer increasing, which may be caused by the thickness dependence of the work function of FM. These results show the possibility of engineering the deterministic field-free switching by combining the symmetry breaking and the materials design of the HM/FM interface.
重金属（HM）/铁磁金属（FM）结构中的自旋轨道转矩（SOT）在下一代低功耗和高密度自旋电子存储器及逻辑应用方面具有潜力。对于垂直磁化的SOT切换，外部磁场对于打破镜面对称性是不可避免的，这对于高密度纳米电子应用来说并不实用。在这项工作中，我们研究了各种横向不对称多层膜中的电流诱导无场SOT切换和SOT垂直有效场（Hzeff），其中不对称性是通过以楔形生长FM层引入的。我们表明，通过楔入FM层来设计结构不对称性是实现无场SOT切换的通用方案。此外，通过比较不同样品中（Hzeff）对FM层厚度的依赖性，我们表明效率（Hzeff / ， 是电流密度）对HM/FM界面和FM层厚度敏感。对于薄FM厚度， 的符号与附着在FM层上的HM层的自旋霍尔角（ ）有关。 随着FM层厚度的增加而改变其符号，这可能是由FM功函数的厚度依赖性引起的。这些结果表明，通过结合HM/FM界面的对称性破坏和材料设计来实现确定性无场切换的可能性。
