Spin-orbit torque in a three-fold-symmetric bilayer and its effect on magnetization dynamics

Area of Science:

• Condensed Matter Physics
• Materials Science
• Spintronics

Background:

• Perpendicular magnetization switching has been observed in CoPt/CuPt bilayers, attributed to spin-orbit torque (SOT) from the interface's 3m crystallographic symmetry.
• Understanding the nature and contribution of this 3m SOT is crucial for advancing spintronic device applications.

Purpose of the Study:

• To theoretically calculate the angular dependence of the 3m SOT in CoPt/CuPt bilayers.
• To investigate magnetization dynamics under the influence of 3m SOT and Dzyaloshinskii-Moriya interaction (DMI).
• To determine conditions for deterministic magnetization switching.

Main Methods:

• First-principles nonequilibrium Green's function formalism combined with the Anderson disorder model.
• Calculation of the angular dependence of SOT.
• Equations of motion for domain wall dynamics and micromagnetic simulations.

Main Results:

• The calculated 3m SOT magnitude is approximately 20% of the conventional dampinglike SOT in CoPt/CuPt bilayers.
• Deterministic switching requires very high current densities in systems with strong interfacial DMI and Néel domain walls.
• Deterministic switching is achievable at much lower current densities in thicker films with weak interfacial DMI and Bloch domain walls.

Conclusions:

• The 3m SOT plays a role in field-free magnetization switching, though it is less dominant than conventional SOT.
• Film characteristics, specifically DMI strength and domain wall type, significantly influence the current density required for deterministic switching.
• The findings may explain recent experimental observations of efficient switching in certain CoPt/CuPt systems.