Large Spin-Orbit Torque with Multi-Directional Spin Components in Ni₄W

Area of Science:

• Spintronics
• Materials Science
• Condensed Matter Physics

Background:

• Spin-orbit torque (SOT) is crucial for spintronic devices, but conventional materials have limitations.
• High crystal symmetry restricts SOT to in-plane spin generation, hindering efficient magnetization manipulation.
• Low-symmetry materials offer potential for unconventional spin currents and field-free switching, but often with low efficiency.

Purpose of the Study:

• To investigate the SOT properties of the low-symmetry material Ni₄W.
• To evaluate the SOT efficiency and spin polarization characteristics of bulk and W/Ni₄W structures.
• To demonstrate the potential of Ni₄W for field-free switching in spintronic applications.

Main Methods:

• Second harmonic Hall measurements were used to evaluate SOT efficiency.
• Characterization of bulk Ni₄W and W/Ni₄W (5 nm) heterostructures.
• Demonstration of field-free switching of perpendicular magnetization.

Main Results:

• A significant SOT efficiency of 0.3 was achieved in bulk Ni₄W at room temperature.
• Unconventional SOT with out-of-plane and Dresselhaus-like spin components were observed due to Ni₄W's low crystal symmetry.
• An enhanced SOT efficiency of 0.73 was recorded in W/Ni₄W (5 nm), suggesting interfacial or extrinsic contributions.

Conclusions:

• Ni₄W demonstrates high SOT efficiency and unconventional spin generation capabilities.
• The material shows promise for developing energy-efficient spintronic memory and logic devices.
• Ni₄W's low-symmetry nature enables multi-directional SOT for field-free magnetic switching.