Antiferromagnetic THz-frequency Josephson-like Oscillator Driven by Spin Current

TL;DR

This paper proposes a theoretical design for a room-temperature, tunable THz-frequency oscillator using a bi-layer of heavy metal and antiferromagnetic material driven by spin current, offering a compact alternative to cryogenic devices.

Contribution

It introduces a novel antiferromagnetic THz oscillator driven by spin current, functioning at room temperature, and mimics Josephson junction behavior without cryogenic requirements.

Findings

Frequency range of 0.1-2.0 THz controlled by current density.

Achieves THz signals with amplitude exceeding 1 V/cm.

Operates similarly to cryogenic Josephson oscillators at room temperature.

Abstract

The development of compact and tunable room temperature sources of coherent THz-frequency signals would open a way for numerous new applications. The existing approaches to THz-frequency generation based on superconductor Josephson junctions (JJ), free electron lasers, and quantum cascades require cryogenic temperatures or/and complex setups, preventing the miniaturization and wide use of these devices. We demonstrate theoretically that a bi-layer of a heavy metal (Pt) and a bi-axial antiferromagnetic (AFM) dielectric (NiO) can be a source of a coherent THz signal. A spin-current flowing from a DC-current-driven Pt layer and polarized along the hard AFM anisotropy axis excites a non-uniform in time precession of magnetizations sublattices in the AFM, due to the presence of a weak easy-plane AFM anisotropy. The frequency of the AFM oscillations varies in the range of 0.1-2.0 THz with the driving current in the Pt layer from $10^8\text{A}/\text{cm}^2$ to $10^9\text{A}/\text{cm}^2$. The THz-frequency signal from the AFM with the amplitude exceeding 1 V/cm is picked up by the inverse spin-Hall effect in Pt. The operation of a room-temperature AFM THz-frequency oscillator is similar to that of a cryogenic JJ oscillator, with the energy of the easy-plane magnetic anisotropy playing the role of the Josephson energy.