Controlled Two-Dimensional Ferromagnetism in 1T-CrTe2: The Role of Charge Density Wave and Strain

Transition metal dichalcogenides are promising candidates to show long-range ferromagnetic order in the single-layer limit. Based on ab initio calculations, we report the emergence of a charge density wave (CDW) phase in monolayer 1T-CrTe2. We demonstrate that this phase is the ground state in the single-layer limit at any strain value. We obtain an optical phonon mode of 1.96 THz that connects the CDW phase with the undistorted 1T phase. Localization of the a1g orbital of CrTe2 produces an out-of-plane orientation of the magnetic moments, circumventing the restrictions of the Mermin-Wagner theorem and producing ferromagnetic long-range order in the two-dimensional limit. This orbital localization is enhanced by the CDW phase. Tensile strain also increases the localization of this orbital, driving the system to become ordered. CrTe2 becomes an example of a material where the CDW phase produces the stabilization of the long-range ferromagnetic order. Our results show that both strain and phase switching are mechanisms to control the 2D ferromagnetic order of CrTe2.