Large spin-orbit torque generated by amorphous iron silicide

Abstract Spin-orbit torque (SOT) shows great potential for next-generation memory technology. Conventionally, the underlying physics of SOT has been associated with heavy (high-Z) elements and/or intrinsic bandstructure. Here, we report large spin-orbit torques in amorphous iron silicides, a material that involves only light elements and for which an E-k relationship cannot be defined. We have achieved a spin-orbit torque efficiency as high as 2.0 (i.e. 200%), which is comparable to the highest known spin-orbit torque efficiency material system (topological insulator). We also found that the SOT efficiency shows a functional dependence on the relative position of the Fermi level with respect to the density of states, indicating an intrinsic origin. In addition, the SOT efficiency does not follow the decreasing trend with increasing conductivity as is typically found in conventional materials. The conventional trend makes it difficult to alter the product of SOT efficiency and conductivity, thereby limiting the overall efficiency of a SOT device. Our results demonstrate a new class of material system, amorphous silicides, where it is possible to generate strong spin currents and where the underlying physics of spin current generation is very different, allowing to circumvent some of the fundamental limitations of conventional materials.