Anomalous Spin-Current Generation Induced by Low Crystalline Symmetry

Area of Science:

• Spintronics
• Materials Science
• Condensed Matter Physics

Background:

• Field-free switching of perpendicular magnetization using spin-orbit torque (SOT) is crucial for advanced semiconductor and logic devices.
• Existing methods to break mirror symmetry for SOT often involve complex techniques.
• Low-symmetry materials offer a potential route to simplify symmetry breaking for spin current generation.

Purpose of the Study:

• To investigate the potential of low-symmetry monoclinic materials for generating unconventional spin currents.
• To demonstrate field-free SOT switching using spin currents derived from monoclinic materials.
• To explore the role of crystallographic direction in spin current polarization and SOT efficiency.

Main Methods:

• Symmetry analysis of low-symmetry monoclinic crystal structures.
• Spin-torque ferromagnetic resonance (ST-FMR) experiments.
• Investigation of spin current generation and magnetization switching in monoclinic WO2.

Main Results:

• Monoclinic WO2 was identified as a material capable of breaking symmetry protection for spin-current polarization.
• Out-of-plane polarized spin currents were generated in WO2, dependent on the crystallographic direction of current flow.
• Efficient field-free SOT switching of perpendicular magnetization was achieved at room temperature in monoclinic WO2.

Conclusions:

• Low-symmetry materials, such as monoclinic WO2, can act as efficient spin sources for spintronic applications.
• Unconventional spin currents with specific polarization can be generated by exploiting crystallographic symmetries.
• This approach offers a simplified pathway for achieving field-free SOT switching, with broad prospects for future spintronic devices.