Field-Assisted Sub-Terahertz Spin Pumping and Auto-Oscillation in NiO

TL;DR

This paper demonstrates that applying a magnetic field to NiO, an easy-plane antiferromagnet, enables efficient sub-terahertz spin pumping and auto-oscillation, overcoming previous limitations due to polarization constraints.

Contribution

It reveals that magnetic field manipulation can enable coherent spin pumping and auto-oscillation in NiO, expanding the material options for sub-terahertz spintronic devices.

Findings

Magnetic field modifies resonance mode polarization in NiO.

Field reduces threshold for Néel vector auto-oscillation.

Achieves spin pumping strength comparable to easy-axis AFMs.

Abstract

Spin pumping converting sub-terahertz electromagnetic waves to DC spin currents has recently been demonstrated in antiferromagnets (AFMs) with easy-axis magnetic anisotropy. However, easy-plane AFMs such as NiO, which are easier to prepare experimentally, are considered to be bad candidates for spin pumping because the N\'{e}el vector oscillation is linearly polarized, placing a major restriction on the material choice for practical applications. Through a case study of NiO, we show that an applied magnetic field below the spin-flop transition can substantially modify the polarization of the resonance eigenmodes, which enables coherent sub-terahertz spin pumping as strong as that in easy-axis AFMs. In addition, we find that an applied magnetic field can significantly reduce the threshold of N\'{e}el vector auto-oscillation triggered by spin-transfer torques. These prominent field-assisted effects can greatly facilitate spintronic device engineering in the sub-terahertz frequency regime.