Spin transport and proximity induced magnetism in thin film structures*

Critical physical mechanisms occur across the interfaces between magnetic (FM) and non-magnetic heavy metal (HM) thin-film layers. Key examples are the enhancement of magnetic damping, which occurs via interfacial effects and the pumping of spin-current into NM layers, and spin-orbit torque (SOT) switching from the propagation of spin-current from a HM into a FM layer. The linkage between different interfacial phenomena has been the subject of debate, including the role of proximity induced magnetisation (PIM) in spin transport across FM/HM interfaces [1]. Debate has also surrounded the spin-diffusion length from spin-pumping analysis [2] and spin-pumping through insulating layers [3]. The focus here is on spin-transport across the interface. PIM in Pt is discussed first in heavy metals layered with ferro and ferri-magnetic materials [4]. Spin transport across FM/NM interfaces is then introduced and the effects of interface structure and NM thickness and a new fuller physical description for the analysis of spin-transport from spin-pumping in FM/NM is presented [2]. This shows that both the NM and FM layer thicknesses should be systematically studied and also shows the need to incorporate a thickness dependence for the spin-diffusion length in the NM layer [2]. Finally, very recent work demonstrating the relationship between PIM and enhanced damping is described. Element specific x-ray magnetic circular dichroism and ferromagnetic resonance measurements in both CoFe/Au/Pt and NiFe/Au/Pt thin film samples with varying Au thickness show an approximately linear relationship between the magnitude of Pt PIM and the damping enhancement [1].