Long spin coherence length and bulk-like spin-orbit torque in ferrimagnetic multilayers

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Spintronics utilizes current-induced spin torques for magnetization switching.
• Ferromagnetic materials require high switching currents due to surface-limited spin transfer torque, hindering high-density applications.
• Developing energy-efficient spintronic devices necessitates overcoming current limitations in ferromagnetic materials.

Purpose of the Study:

• To investigate spin coherence length and torque characteristics in antiferromagnetically coupled ferrimagnetic multilayers.
• To explore the potential of ferrimagnetic multilayers for efficient magnetization switching.
• To contrast spin torque behavior in ferrimagnetic versus ferromagnetic multilayers.

Main Methods:

• Fabrication and characterization of ferrimagnetic Co/Tb and ferromagnetic Co/Ni multilayers.
• Measurement of transverse spin current propagation through varying layer thicknesses.
• Analysis of magnetization switching efficiency as a function of ferrimagnet thickness.

Main Results:

• A long spin coherence length was observed in ferrimagnetic Co/Tb multilayers, allowing spin current to penetrate >10 nm.
• In contrast, spin current was fully absorbed by a 1-nm-thick ferromagnetic Co/Ni multilayer.
• Ferrimagnetic multilayers exhibited bulk-like torque characteristics, with switching efficiency peaking at 8 nm thickness, unlike the 1/thickness dependence in ferromagnets.

Conclusions:

• Antiferromagnetically coupled ferrimagnetic multilayers offer a promising avenue for efficient spintronics.
• The observed bulk-like torque characteristics in ferrimagnets can significantly reduce switching currents.
• These findings are crucial for advancing the development of energy-efficient, high-density non-volatile spintronic applications.