Large magneto-optical effects and magnetic anisotropy energy in two-dimensional Cr2Ge2Te6 (original) (raw)

Atomically thin ferromagnetic (FM) films were recently prepared by mechanical exfoliation of bulk FM semiconductor Cr2Ge2Te6. They provide a platform to explore novel two-dimensional (2D) magnetic phenomena, and offer exciting prospects for new technologies. By performing systematic ab initio density functional calculations, here we study two relativity-induced properties of these 2D materials [monolayer (ML), bilayer (BL) and trilayer (TL) as well as bulk], namely, magnetic anisotropy energy (MAE) and magneto-optical (MO) effects. Competing contributions of both magneto-crystalline anisotropy energy (C-MAE) and magnetic dipolar anisotropy energy (D-MAE) to the MAE, are computed. Calculated MAEs of these materials are large, being in the order of ∼0.1 meV/Cr. Interestingly, we find that the out-of-plane magnetic anisotropy is preferred in all the systems except the ML where an in-plane magnetization is favored because here the D-MAE is larger than the C-MAE. Crucially, this explains why long-range FM order was observed in all the few-layer Cr2Ge2Te6 except the ML because the out-of-plane magnetic anisotropy would open a spin-wave gap and thus suppress magnetic fluctuations so that long-range FM order could be stabilized at finite temperature. In the visible frequency range, large Kerr rotations up to ∼1.0 • in these materials are predicted and they are comparable to that observed in famous MO materials such as PtMnSb and Y3Fe5O12. Moreover, they are ∼100 times larger than that of 3d transition metal MLs deposited on Au surfaces. Faraday rotation angles in these 2D materials are also large, being up to ∼120 deg/µm, and are thus comparable to the best-known MO semiconductor Bi3Fe5O12. These findings thus suggest that with large MAE and MO effects, atomically thin Cr2Ge2Te6 films would have potential applications in novel magnetic, MO and spintronic nanodevices.