Spin Hall Magnetoresistance in Metallic Bilayers

Area of Science:

• Condensed Matter Physics
• Materials Science
• Spintronics

Background:

• Spin Hall magnetoresistance (SMR) is a phenomenon observed in heavy metal (HM) and ferromagnetic metal (FM) bilayers.
• Previous studies focused on HM/ferromagnetic insulator systems, limiting understanding of metallic interfaces.

Purpose of the Study:

• Investigate SMR in metallic HM/FM bilayers, specifically W/CoFeB.
• Develop a model to explain the observed SMR behavior and material properties.
• Compare SMR in metallic systems to insulating ones.

Main Methods:

• Fabrication and characterization of W/CoFeB metallic bilayers.
• Experimental measurement of SMR across varying temperatures and layer thicknesses.
• Development of a theoretical model incorporating spin current absorption in the FM layer.

Main Results:

• Achieved a nearly tenfold increase in SMR in W/CoFeB compared to HM/ferromagnetic insulator systems.
• Observed SMR increase with decreasing temperature, independent of W layer resistivity.
• The developed model accurately predicts SMR dependence on HM layer thickness and temperature.

Conclusions:

• Metallic FM layers play a crucial role in spin transmission across HM/FM interfaces.
• The model allows for precise determination of HM layer spin Hall angle and spin diffusion length.
• Temperature-dependent spin polarization of the FM layer is key to understanding SMR variations.