Excitation and detection of coherent sub-terahertz magnons in ferromagnetic and antiferromagnetic heterostructures

TL;DR

This paper demonstrates the computational excitation and detection of coherent sub-terahertz magnons in ferromagnetic and antiferromagnetic heterostructures using ultrafast optical pulses, revealing potential for high-speed magnonic devices.

Contribution

It introduces a coupled dynamical phase-field model to simulate magnon excitation and electromagnetic emission in FM and AFM thin films, highlighting a new method for sub-THz magnon control.

Findings

Sub-THz magnons can be excited via photoinduced acoustic pulses.

Emitted EM waves carry spectral information of magnon modes.

Detection of sub-THz magnons is feasible with designed heterostructures.

Abstract

Excitation of coherent high-frequency magnons (quanta of spin waves) is critical to the development of high-speed magnonic devices. Here we computationally demonstrate the excitation of coherent sub-terahertz (THz) magnons in ferromagnetic (FM) and antiferromagnetic (AFM) thin films by a photoinduced picosecond acoustic pulse. Analytical calculations are also performed to reveal the magnon excitation mechanism. Through spin pumping and spin-charge conversion, these magnons can inject sub-THz charge current into an adjacent heavy-metal film which in turn emits electromagnetic (EM) waves. Using a dynamical phase-field model that considers the coupled dynamics of acoustic waves, spin waves, and EM waves, we show that the emitted EM wave retains the spectral information of all the sub-THz magnon modes and has a sufficiently large amplitude for near-field detection. These predictions indicate that the excitation and detection of sub-THz magnons can be realized in rationally designed FM or AFM thin-film heterostructures via ultrafast optical-pump THz-emission-probe spectroscopy.