Electrostatic Control of Magnetism in Van Der Waals Ferromagnets

Ivan Verzhbitskiy

Control of magnetism via electric fields is a long-standing exciting challenge of fundamental significance for future spintronic devices. Recent discovery of two-dimensional magnetism in van der Waals systems such as CrI3, Fe3GeTe2, and Cr2Ge2Te6 (CGT) highlights their unique potential as a platform to probe the interplay between charge and magnetic ordering [1]. Here, we report the first observation of carrier-induced ferromagnetic order in heavily doped thin crystals of CGT [2]. Upon degenerate electron doping, the CGT transistor exhibits clear hysteresis in the magnetoresistance (MR), which is a distinctive signature of ferromagnetism. Surprisingly, the hysteresis persists up to 200 K, which is in contrast to undoped CGT whose Curie temperature is only 61 K. We demonstrate that the Curie temperature can be modulated over 140 K by altering the electron density. Further, we find the magnetic easy-axis of doped CGT to lie within the plane of the crystal. This is in stark contrast to the out-of-plane magnetic easy-axis of the pristine CGT. We attribute these changes to emergence of the double-exchange interaction mediated by free carriers. This mechanism dominates over superexchange interaction, which is responsible for the ferromagnetic order in undoped CGT. Our calculations show that the magnetic anisotropy energy changes sign in degenerate doping limit, in agreement with our experimental observations. Our findings reveal a unique role of the electric field in tailoring the magnetic anisotropy and leading exchange interaction in semiconducting 2D ferromagnets.

[1] Gibertini, M.; Koperski, M.; Morpurgo, A. F. & Novoselov, K. S. Magnetic 2D materials and heterostructures. Nat. Nanotechnol. 14, 408–419 (2019).

[2] Verzhbitskiy, I.; Kurebayashi, H.; Cheng, H.; Zhou, J.; Khan, S.; Feng, Y. P. & Eda, G. Controlling the magnetic anisotropy in Cr2Ge2Te6 by electrostatic gating. Nat. Electron. (2020), DOI:https://doi.org/10.1038/s41928-020-0427-7