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

Correction to “A Narrowband Spintronic Terahertz Emitter Based on Magnetoelastic Heterostructures”

“…To correctly calculate the magnetic dipole radiation, an in-house finite-difference time-domain (FDTD) solver of Maxwell’s equations was developed. Details of this FDTD solver and its validation are provided in our recent publication . In the original paper, we attributed the THz radiation to the THz standing spin wave that forms due to the interference between the incident and reflected THz exchange spin waves.…”

“…The J c then produces the THz electromagnetic pulse via electric dipole radiation. The validity and efficacy of this new design have also been demonstrated in our recent paper, where we utilized this approach to detect the high-order THz standing spin wave confined in a magnetic thin film. To obtain strong THz emission, a large spin Hall angle for the spin-charge conversion layer and large spin mixing conductance are preferred.…”

“…Here, we consider Pt as a typical example because the spin pumping and the spin-charge conversion via ISHE at the magnet/Pt interfaces have been well studied. − The calculation of spin pumping and spin-charge conversion was performed in a coupled fashion with our in-house FDTD solver for Maxwell’s equations. Details of the calculation are also provided in our recent publication . Based on the updated calculation and results, we conclude that the multicycle and narrowband feature of the THz pulse remains unchanged.…”

“…Details of this FDTD solver and its validation are provided in our recent publication. 1 In the original paper, we attributed the THz radiation to the THz standing spin wave that forms due to the interference between the incident and reflected THz exchange spin waves. However, using the FDTD solver, it is found that the magnetic dipole radiation from the THz standing spin wave is negligible (with a peak amplitude of 0.02 V/m).…”

“…Details of the calculation are also provided in our recent publication. 1 Based on the updated calculation and results, we conclude that the multicycle and narrowband feature of the THz pulse remains unchanged. m y (z,t) − m y (z,t = 0) is evaluated using the m y at t = 0 ps as the reference, where t = 0 ps is defined as the moment the strain pulse propagates into the Fe film from its bottom surface.…”