Distinct spin–lattice and spin–phonon interactions in monolayer magnetic CrI₃

Abstract

We apply the density-functional theory to study various phases (including non-magnetic (NM), anti-ferromagnetic (AFM), and ferromagnetic (FM)) in monolayer magnetic chromium triiodide (CrI3), a recently fabricated 2D magnetic material. It is found that: (1) the introduction of magnetism in monolayer CrI3 gives rise to metal-to-semiconductor transition; (2) the electronic band topologies as well as the nature of direct and indirect band gaps in either AFM or FM phases exhibit delicate dependence on the magnetic ordering and spin-orbit coupling; and (3) the phonon modes involving Cr atoms are particularly sensitive to the magnetic ordering, highlighting distinct spin-lattice and spin-phonon coupling in this magnet. First-principles simulations of the Raman spectra demonstrate that both frequencies and intensities of the Raman peaks strongly depend on the magnetic ordering. The polarization dependent A1g modes at 77 cm-1 and 130 cm-1 along with the Eg mode at about 50 cm-1 in the FM phase may offer a useful fingerprint to characterize this material. Our results not only provide a detailed guiding map for experimental characterization of CrI3, but also reveal how the evolution of magnetism can be tracked by its lattice dynamics and Raman response.

Nonvolatile Electrical Control and Heterointerface‐Induced Half‐Metallicity of 2D Ferromagnets

“…Theoretically predicted in 2015 and experimentally realized by Xu's group in 2017, the single‐layer CrI 3 exhibits the intrinsic ferromagnetism with the magnetic moment of about 3.0 µ B per Cr atom and Curie temperature of 45 K. The discovery of CrI 3 monolayer, the first single‐layer vdW ferromagnets demonstrated in experiments, opened the door for low‐temperature nanospintronics. Due to its potential applications and being an excellent model of 2D vdW ferromagnets for proof‐of‐principle demonstrations, CrI 3 monolayer is among the most studied atomically thin vdW ferromagnets in both theory and experiments …”

Magnetic-Field-Induced Quantum Phase Transitions in a van der Waals Magnet

“…The second group consists of two modes M 1 and M 2 that were previously shown to be antisymmetric and attributed to surface magnetic excitations [15], showing up in the LL channel here. The third kind is exclusively very lowfrequency modes M 0 that, however, have neither been detected experimentally [15,24,25] nor predicted theoretically [26,27] before in Raman studies and are present in both LL and LR channels. Symmetrywise, these M 0 -type modes violate the selection rules for the rhombohedral crystal structure and the FM order.…”

Relativistic exchange interactions in CrX3 ( X=Cl , Br, I) monolayers

“…Strong spin-phonon coupling has been reported for CrX 3 systems [89,90]. Since phonons and magnons in this class of materials have similar energies [81,89], even a small coupling can produce a substantial hybridization between the two types of excitations. One can expect the exchange interactions will be sensitive to any structural distortions, due to the NN bond angle being close to 90 • and the internal competition between FM and AFM contributions.…”