Controlling the nonequilibrium interlayer exchange coupling in asymmetric magnetic tunnel junctions

Area of Science:

• Condensed matter physics
• Spintronics
• Materials science

Background:

• Spin torque is crucial for magnetic tunnel junction (MTJ) device operation.
• Understanding bias-dependent spin torque behavior is essential for advanced spintronic applications.
• Existing experimental results on fieldlike spin torque (T⊥) show apparent contradictions.

Purpose of the Study:

• To predict and explain the oscillatory bias behavior of fieldlike spin torque (T⊥) in MTJs.
• To identify a mechanism for controlling T⊥ bias dependence.
• To reconcile conflicting experimental observations in the literature.

Main Methods:

• Theoretical prediction of T⊥ behavior.
• Analysis of band filling asymmetry in ferromagnetic leads.
• Investigation of interlayer exchange coupling (IEC) mechanisms.

Main Results:

• Predicted an oscillatory bias behavior for T⊥.
• Demonstrated selective control of T⊥ via band filling asymmetry.
• Showed that T⊥ can exhibit linear or quadratic low-bias behavior.
• Identified the underlying mechanism involving interplay of four independent IECs for majority- and minority-spin bands.

Conclusions:

• The interplay of spin-dependent IECs provides a unified mechanism for T⊥ bias behavior.
• Band filling asymmetry offers a route to tune and control T⊥.
• This work reconciles contradictory experimental findings on spin torque in MTJs.