Antiferromagnetic s-d exchange coupling in GaMnAs

Area of Science:

• Condensed Matter Physics
• Materials Science
• Semiconductor Spintronics

Background:

• Diluted magnetic semiconductors like GaMnAs are key for spintronic applications.
• Understanding electron-impurity interactions is crucial for controlling spin dynamics.
• Previous models did not fully capture the complexity of exchange interactions in GaMnAs.

Purpose of the Study:

• To investigate the nature of the exchange interaction between conduction band electrons and Mn2+ impurities in GaMnAs/AlGaAs quantum wells.
• To determine the contribution of kinetic exchange to the s-d exchange parameter.
• To explore the influence of quantum confinement on spin dynamics and exchange interactions.

Main Methods:

• Measurements of coherent electron spin dynamics in Ga1-xMnxAs/Al0.4Ga0.6As quantum wells.
• Analysis of the s-d exchange parameter (N0alpha) as a function of quantum well width.
• Polarization-resolved photoluminescence spectroscopy to probe valence band exchange splitting.

Main Results:

• An antiferromagnetic (negative) exchange interaction was observed between s-like conduction band electrons and d-shell electrons of Mn2+ impurities.
• The s-d exchange parameter (N0alpha) showed dependence on well width, indicating a significant kinetic exchange contribution.
• Extrapolation to bulk GaMnAs yielded N0alpha = -0.09 ± 0.03 eV, confirming antiferromagnetic s-d exchange as a bulk property.
• Photoluminescence data revealed discrepancies with simple models, suggesting complex exchange splitting in the valence band.

Conclusions:

• Antiferromagnetic s-d exchange is an intrinsic bulk property of GaMnAs.
• Kinetic exchange plays a substantial role in the observed s-d interaction.
• The electronic structure and exchange interactions in the valence band of GaMnAs are more complex than previously understood.