Magnetic Anisotropy and Magnetic Ordering of Transition-Metal Phosphorus Trisulfides

A magnetic model with an unprecedentedly large number of parameters was determined from first-principles calculations for transition-metal phosphorus trisulfides (TMPS₃'s), reproducing the measured magnetic ground states of bulk TMPS₃'s. Our Monte Carlo simulations for the critical temperature, magnetic susceptibility, and specific heat of bulk and few-layer TMPS₃'s agree well with available experimental data and show that the antiferromagnetic order of TMPS₃'s persists down to monolayers. Remarkably, the orbital polarization, neglected in recent first-principles studies, dramatically enhances the magnetic anisotropy of FePS₃ by almost 2 orders of magnitude. A recent Raman study [Kim, K., Nat. Commun. 2019, 10, 345] claimed that magnetic ordering is absent in monolayer NiPS₃ but simultaneously reported a strong two-magnon continuum; we show that the criterion used to judge magnetic ordering therein is invalid for monolayer NiPS₃, providing an understanding of the two seemingly contradictory experimental results. The rich predictions on the magnetic susceptibility and specific heat of few-layer TMPS₃'s await experimental verifications.