Magnetic interface profiles in amorphous spin-orbit torque switching structures

Spin-orbit torque-induced (SOT) magnetization switching is an important effect in spintronic applications such as magnetic random access memories, and spin logic devices. It is a very active topic of research and a number of different materials systems have been studied. SOT switching devices are layered structures composed of a thin magnetic layer (M) such as TbCo adjacent to a polycrystalline heavy metal (HM) layer such as Pt, Ta or W. The heavy metal layer is used to supply a spin current which generates the torque to switch the magnetic layer. A figure of merit for SOT switching is the switching efficiency which depends on the properties of the HM and the spin transport across the interface. The interface between the two layers is therefore critical. At the interface between a magnetic and non-magnetic material it is known that a magnetization can be induced in the non-magnetic material and this is known as the magnetic proximity effect. Despite its importance the magnetic proximity effect is often not considered in SOT switching studies. The objective is to determine the magnetization profile of HM|M multilayers with PNR measurements, with WSi, TaSi, and Pt as the HM and CoAlZr as the magnetic layer. This will allow us to determine whether the magnetic interfaces are sharp or whether the magnetization varies smoothly across the interface into the HM layer due to the magnetic proximity effect.

自旋轨道力矩诱导（SOT）磁化翻转是自旋电子学应用中的重要效应，可应用于磁随机存取存储器、自旋逻辑器件等场景，当前为研究热点，已有诸多不同材料体系被相关研究探索。SOT翻转器件为层状结构，由紧邻多晶重金属（HM）层的磁性薄层（M）组成，其中重金属层可选用铂（Pt）、钽（Ta）或钨（W）等材料，磁性薄层则可采用铽钴（TbCo）这类材料。重金属层的功能是提供自旋流，进而产生力矩以实现磁性薄层的磁化翻转。评价SOT翻转性能的关键品质因数为翻转效率，其取决于重金属层的材料特性与界面处的自旋输运行为，因此两层之间的界面对翻转效率具有关键影响。已知在磁性与非磁性材料的界面处，非磁性材料中可感应出磁化强度，该现象被称为磁邻近效应。尽管磁邻近效应具有重要意义，但在当前的SOT翻转相关研究中，该效应往往未被纳入考量。本研究的目标为：针对以硅化钨（WSi）、硅化钽（TaSi）及铂（Pt）作为重金属层、钴铝锆（CoAlZr）作为磁性层的HM|M多层膜，通过极化中子反射（PNR）测量确定其磁化分布，以此判断界面是否为突变界面，或是因磁邻近效应导致磁化强度在跨界面进入重金属层的过程中呈现平滑变化。