Exfoliating biocompatible ferromagnetic Cr-trihalide monolayers

Abstract

In addition to spintronics another motivation for exploring ferromagnetic two-dimensional materials is for biomedical applications such as magnetic labeling and hyperthermia treatment of tumors. Unfortunately, the widely studied Mn-containing monolayer is not biocompatible, although it is ferromagnetic. Here using first principles calculations combined with Monte Carlo simulations based on the Ising model, we systematically study a class of 2D ferromagnetic monolayers CrX3 (X = Cl, Br, I). The feasibility of exfoliation from their layered bulk phase is confirmed by the small cleavage energy and high in-plane stiffness. Spin-polarized calculations, combined with self-consistently determined Hubbard U that accounts for strong correlation energy, demonstrate that CrX3 (X = Cl, Br, I) monolayers are ferromagnetic and that Cr is trivalent and carries a magnetic moment of 3 μ(B); the resulting Cr(3+) ions are biocompatible. The corresponding Curie temperatures for CrCl3, CrBr3 and CrI3 are found to be 66, 86, and 107 K, respectively, which can be increased to 323, 314, and 293 K by hole doping. The biocompatibility and ferromagnetism render these Cr-containing trihalide monolayers unique for applications.

Magnetic behavior and spin-lattice coupling in cleavable van der Waals layered CrCl3 crystals

“…The inset shows a separate specimen determined to be one monolayer thick. It is expected that the single-layer CrCl 3 may display ferromagnetism at low temperature, as observed in CrI 3 [30] and as predicted by first principles calculations for all of the chromium trihalides [19,20].…”

“…Other recently discovered materials include Fe 3 GeTe 2 [14], a metal with itinerant ferromagnetism below T C =220-230 K [14][15][16]. Chromium triiodide, and transition metal halides in general [17], have also been put forth as candidates for cleavable magnetic materials [18][19][20][21]. Experimentally, CrI 3 is a ferromagnet with T C = 61 K [18,22,23], CrBr 3 is a ferromagnet with T C = 37 K [24], and CrCl 3 is an antiferromagnet with an ordering temperature near 17 K [25,26].…”

“…Other theoretical studies focus mainly on CrCl 3 monolayers. Liu et al observed ferromagnetic order below 66 K in Monte Carlo simulations of monolayers, and suggested that hole doping should increase the Curie temperature [20]. The cleavage energy in the bulk crystal was calculated using a van der Waals density functional (vdW-DF) method to account for the dispersion forces in the bulk crystal.…”

Electronic and magnetic properties of monolayer α-RuCl3: a first-principles and Monte Carlo study

“…22 For instance, Liu et al 23 investigate the ferromagnetism in monolayer Crtrihalides (CrX 3 (X=Cl, Br, I)) using density functional theory (DFT) combined with the self-consistently determined Hubbard U approach (DFT+U scf ) and Monte Carlo (MC) simulations that based on Ising model. CrBr 3 was obtained as the first ferromagnetic (FM) semiconductor in 1960.…”

Inhomogeneous strain-induced half-metallicity in bent zigzag graphene nanoribbons

“…[1][2][3][4] Since the first theoretical prediction, 5 great efforts have been devoted to identify or design materials with HM properties. [6][7][8][9][10][11][12][13][14] So far, HM has been experimentally demonstrated in bulk systems, e.g., ferromagnetic manganese perovskite. 6 However, despite great efforts, 7-14 the actual realization of HM in low dimensional materials, especially in two-dimensional (2D) single atomic/molecular layer, has not been realized.…”