Strain-tunable ferromagnetism and chiral spin textures in two-dimensional Janus chromium dichalcogenides

Using first-principles calculations and micromagnetic simulations, we systematically investigate the magnetic properties of two-dimensional Janus chromium dichalcogenides ($\mathrm{Cr}X\mathrm{Te}, X=\mathrm{S}$, Se) under strain. We find that the CrSTe monolayer has high Curie temperature ($T_c$) of 295 K and an out-of-plane magnetic anisotropy. The CrSeTe monolayer has large Dzyaloshinskii-Moriya interaction (DMI) which can host chiral Néel domain wall (DW), and under an external magnetic field, the skyrmion states can be induced. As tensile strain increases, ferromagnetic exchange coupling and perpendicular magnetic anisotropy of Janus $\mathrm{Cr}X\mathrm{Te}$ monolayers both increase significantly, and the magnitude of DMI is reduced, which results in the giant ferromagnetism enhancement. Interestingly, for CrSeTe monolayer, distinct spin textures from chiral DW to uniform ferromagnetic states are induced under tensile strain. Moreover, the diameter and density of skyrmions in CrSeTe can be tuned by the amplitude of external magnetic field and strain. These findings highlight that the Janus $\mathrm{Cr}X\mathrm{Te}$ monolayers as good candidates for spintronic nanodevices.

Figure 1

(a) Top view and side view of crystal structures and (b) Phonon dispersions of Janus $\mathrm{Cr}X\mathrm{Te}$ monolayers. (c) The nearest-neighboring exchange coupling $J$, (d) single-ion anisotropy $K$, and (e) in-plane DMI component $d_{\parallel }$ as functions of strain in Janus $\mathrm{Cr}X\mathrm{Te}$ monolayers.

Figure 2

(a) Schematic diagrams of Cr-Se/Te-Cr superexchange and Cr-Cr direct exchange couplings in Janus CrSeTe monolayer. (b) Bond lengths of Cr–Cr, Cr–Te, and Cr–Se as functions of the strain.

Figure 3

(a) Atom-resolved MAE of Janus CrSeTe monolayer as functions of the strain. (b), (c) MAE contributions from $5p$ orbitals hybridization, and (d), (e) the projected density of states of Te in Janus CrSeTe monolayer under 0 and 5% tensile strain.

Figure 4

Atom-resolved localization of the SOC energy difference $\mathrm{\Delta }{E}_{\mathrm{soc}}$ in Janus $\mathrm{Cr}X\mathrm{Te}$ monolayer. Black, red, and blue bars represent $\mathrm{\Delta }{E}_{\mathrm{soc}}$ of $\mathrm{Cr}X\mathrm{Te}$ monolayers under 0, 2, and 4% tensile strain, respectively.

Figure 5

(a) Distinct spin textures for CrSeTe monolayer under increased tensile strains and external fields in 10 K. The color map indicates the out-of-plane spin component of Cr atoms. The curie temperatures ($T_c$) of (b) CrSeTe and (c) CrSTe monolayers under tensile strains.