用BiSePt合金提高自旋轨道转矩效率

Spin-orbit torque efficiency improved by BiSePt alloy

自旋轨道转矩器件实现快速高效的磁性操作,需要提供自旋流的强自旋轨道耦合层具有高的电荷-自旋密度转换效率,以及低的电阻率.本文采用磁控溅射方法生长具有面内磁性的BiSePt合金/Co异质结构,对比BiSePt合金采用共溅射及交替溅射两种生长方式,研究了不同配比下的自旋轨道转矩效率(SOT效率)与合金电阻率.Pt掺杂提高了合金层的金属性,但是逐渐破坏Bi_(2)Se_(3)非晶表面的拓扑序,随着Pt组分的增加,两种竞争的机制使得合金层的自旋霍尔电导率随浓度配比有非单调变化,并且在Bi_(2)Se_(3)组分为67%的配比处达到了优值.相比共溅射方式,交替溅射方式生长合金层的电导率及自旋霍尔角较小,这归因于界面散射的增强及Pt对自旋流的过滤效应.相比于传统的纯重金属Pt和Ta等,以及拓扑绝缘体Bi_(2)Se_(3)等材料,我们的BiSePt合金实现了与工业匹配的生长条件,较高的SOT效率,以及适中的电阻率,对于SOT器件的实际应用很有意义.

In order to achieve high-efficiency spin-orbit torque devices,higher charge-spin conversion efficiency,and lower resistivity are required in the strong spin-orbit coupling layer that provides the spin current.In this work we prepare BiSePt alloy/Co heterostructures with in-plane magnetic anisotropy by magnetron sputtering deposition.The alloy layer is deposited via one of two procedures,either co-sputtering or alternative-sputtering.We study the BiSePt alloy samples and find that the spin orbit torque(SOT)efficiency decreases with the increase of Pt component,which is attributed to the change of topological order of Bi_(2)Se_(3) amorphous surface,caused by Pt doping.And the resistivity decreases with the increase of Pt component,which depends on the increase of metallic property.Due to the balance of these two competing mechanisms,the spin Hall conductivity of the alloy layer varies non-monotonically with the concentration ratio,and reach an optimal value at a ratio of 67%of Bi_(2)Se_(3) component.With the increase of the Bi_(2)Se_(3) component,the SOT efficiency,electrical resistivity and spin Hall conductance of the alloy layer show different trends.At about 20%–70%,they increase/decrease tardily.At about 70%–100%,the resistivity ascends more prominently than the SOT efficiency,which leads the spin Hall conductance to decrease.Comparing with using the co-sputtering deposition,the electrical conductivity and spin Hall angle of the alloy layer obtained using alternating sputtering deposition are small,which is attributed to the enhancing of interfacial scattering and the filter effect of Pt on the spin flow.In contrast to traditional pure heavy metal materials(such as Pt,Ta)and topological insulator materials like Bi_(2)Se_(3),our BiSePt alloy devices obtained by co-sputtering deposition achieve industry-matched preparation conditions,greater SOT efficiency,and considerable electrical conductivity of the alloy layer,thus making further applications of SOT devices possible.