FeS2 monolayer: a high valence and high-\(T_{\rm C}\) Ising ferromagnet

• Published in: arXiv.org
• Main Authors: Yang, Ke, Ma, Yaozhenghang, Liu, Lu, Yueyue Ning, Lu, Di, Zhou, Yuxuan, Li, Zhongyao, Wu, Hua
• Format: Paper
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 12.01.2024
• Subjects: Anisotropy; Charge transfer; Compressive properties; Ferromagnetism; First principles; High temperature; Ising model; Magnetic materials; Mathematical analysis; Monolayers; Orbitals; Pyrite; Spintronics; Two dimensional analysis
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.2401.06357

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 \(T_{\rm C}\) is 261 K for the pristine FeS\(_2\) monolayer and could be increased to 409 K under the compressive --5\% strain. The high \(T_{\rm C}\) is also reproduced by our Monte Carlo (MC) simulations. Therefore, it is worth exploring the high-\(T_{\rm C}\) Ising FMs in the high valent 2D magnetic materials with degenerate orbitals.