FeS2 monolayer: a high valence and high-$T_{\mathrm{C}}$ Ising ferromagnet

Abstract

Two-dimensional (2D) magnetic materials are of current great interest for their promising applications in spintronics. Strong magnetic coupling and anisotropy are both highly desirable for the achievement of a high temperature magnetic order. Here we propose the unusual high valent FeS${}_2$ hexagonal monolayer as such a candidate for a strong Ising 2D ferromagnet (FM), by spin-orbital state analyses, first-principles calculations, and the renormalized spin-wave theory (RSWT). We find that very importantly, the high valent Fe${}^{4+}$ ion is in the low-spin state ($t_{2g}^4$, $S$=1) with degenerate $t_{2g}$ orbitals rather than the high-spin state ($t_{2g}^3{e}_g^1$, $S$=2). It is the low-spin state that allows to carry a large perpendicular orbital moment and then produces a huge single ion anisotropy (SIA) of 25 meV/Fe. Moreover, the negative charge transfer character associated with the unusual high valence, strong Fe $3d$-S $3p$ hybridization, wide bands, and a small band gap all help to establish a strong superexchange. Indeed, our first-principles calculations confirm the strong FM superexchange and the huge perpendicular SIA, both of which are further enhanced by a compressive strain. Then, our RSWT calculations predict that the FM $T_{\mathrm{C}}$ is 261 K for the pristine FeS${}_2$ monolayer and could be increased to 409 K under the compressive --5\% strain. The high $T_{\mathrm{C}}$ is also reproduced by our Monte Carlo (MC) simulations. Therefore, it is worth exploring the high-$T_{\mathrm{C}}$ Ising FMs in the high valent 2D magnetic materials with degenerate orbitals.

13 pages, 5 figures

References in corpus (8)

• Ground state oxygen holes and the metal-insulator transition in the negative charge transfer rare-earth nickelates
• VI3 - a new layered ferromagnetic semiconductor
• Triaxial magnetic anisotropy in the two-dimensional ferromagnetic semiconductor CrSBr
• The Jeff=1/2 antiferromagnet Sr2IrO4: A golden avenue toward new physics and functions
• Two-dimensional ferromagnetic semiconductor VBr3 with tunable anisotropy
• Fragile Symmetry-Protected Half Metallicity in Two-Dimensional van der Waals Magnets: A Case Study of Monolayer FeCl2
• Unique electronic state in ferromagnetic semiconductor FeCl${}_2$ monolayer
• Magnetic order and its interplay with structure phase transition in van der Waals ferromagnet VI${}_3$

Cited by in corpus (1)

• Measurement-induced transitions beyond Gaussianity: a single particle description