Terahertz Magnetic and Lattice Excitations in van der Waals Ferromagnet VI3

TL;DR

This study combines spectroscopic techniques and DFT calculations to explore the magnetic and lattice dynamics of VI3, revealing structural transitions, phonon behavior, and a THz magnon, highlighting its potential in ultrafast spintronics.

Contribution

It provides new insights into the magnetoelastic coupling and THz magnon excitations in VI3, a 2D van der Waals ferromagnet, with implications for spintronic applications.

Findings

Structural transition at 79 K causes phonon mode splitting.

Detection of a THz-range magnon below 50 K.

Magnetoelastic effects linked to spin-orbit interaction.

Abstract

We use the synergy of infrared, terahertz, and Raman spectroscopies with DFT calculations to shed light on the magnetic and lattice properties of VI3. The structural transition at TS1 = 79 K is accompanied by a large splitting of polar phonon modes. Below TS1, strong ferromagnetic fluctuations are observed. The variations of phonon frequencies at 55 K induced by magnetoelastic coupling enhanced by spin-orbit interaction indicate the proximity of long-range ferromagnetic order. Below TC = 50 K, two Raman modes simultaneously appear and show dramatic softening in the narrow interval around the temperature TS2 of the second structural transition associated with the order-order magnetic phase transition. Below TS2, a magnon in the THz range appears in Raman spectra. The THz magnon observed in VI3 indicates the application potential of 2D van der Waals ferromagnets in ultrafast THz spintronics, which has previously been considered an exclusive domain of antiferromagnets.