Tunable magnetic properties of transition metal doped ${\mathrm{MoS}}_2$

We report a detailed investigation of the electronic and magnetic properties of the transition metal (TM) doped two-dimensional (2D) ${\mathrm{MoS}}_2$ using ab initio calculations. The doping is achieved by substituting two or more Mo atoms by TM atoms of the $3d$ series. Additionally, the effect of codoping on the 2D ${\mathrm{MoS}}_2$ by cation-cation and cation-anion pairs is also investigated. Our results demonstrate that the TM doping of 2D ${\mathrm{MoS}}_2$ leads to a significant reduction of the energy gap and the appearance of magnetic features whose major characteristic is the ferromagnetic coupling of the TM dopants. The latter is found to be significantly enhanced by codoping as demonstrated by codoping with (Co,Cu), (Ni,Cu), (Mn,Cu), and (Mn,Sb) codopant pairs.

Figure 1

Energy gaps (left panel) and magnetic moments (middle and right panels) of single layer ${\mathrm{Mo}}_{62}{\mathrm{TM}}_2{\mathrm{S}}_{128}$ with the TM taken from the $3d$ series. The middle (right) panel includes results for the monodoped (codoped) systems, respectively. In the left panel results for ${\mathrm{Mo}}_{64}{\mathrm{S}}_{128}$ and the defected systems: ${\mathrm{Mo}}_{63}{\mathrm{S}}_{128}$ and ${\mathrm{Mo}}_{64}{\mathrm{S}}_{127}$ are also presented. Defect-free and defected ${\mathrm{MoS}}_2$ structures do not exhibit magnetic moments. In the middle panel, solid (red) squares denote the magnetic moment per unit cell (${\mu }_{\mathrm{u}\text{−}\mathrm{cell}}$) while (green) pluses denote the sum of the magnetic moments of the impurity TM atoms ($2{\mu }_{TM}$). In the right panel blue (solid square and plus symbols) indicates corresponding results for the ${\mathrm{MoS}}_2$ systems codoped with (${\mathrm{Mn}}_2\mathrm{Cu}$), (${\mathrm{Co}}_2\mathrm{Cu}$), and (${\mathrm{Ni}}_2\mathrm{Cu}$). The cationic-anionic codoping (${\mathrm{Mn}}_2{\mathrm{Sb}}_2$) is shown in orange (solid square and plus symbols).

Figure 2

Variation with $U_d$ of the total (per cell) magnetic moment ${\mu }_{\mathrm{cell}}\left(U_d\right)$ and that of the magnetic moments ${\mu }_{TM}\left(U_d\right)$ of the TM-substitutional impurities in ${\mathrm{MoS}}_2$ for $U_d=0.0,2.5$, and $5.5$ eV.

Figure 3

Variation with $U_d$ of the range of the bond lengths of the bonds formed between the TM-substitutional impurity and its 1 nn S anions in ${\mathrm{MoS}}_2$. Maximum (correspondingly minimum) bond lengths are indicated by filled (correspondingly unfilled) symbols for $U_d=0.0,2.5$, and $5.5$ eV. The straight line indicates the unrelaxed TM-S bond lengths.

Figure 4

Band structure and DOS for ${\mathrm{Mo}}_{62}{\mathrm{Ti}}_2{\mathrm{S}}_{128}$ (top) and ${\mathrm{Mo}}_{62}{\mathrm{Cr}}_2{\mathrm{S}}_{128}$ (bottom) obtained using $U_d=5.5$ eV. Spin-up and spin-down lines are indicated in red and blue, respectively, in band structure and DOS plots. In the DOS plots, the total DOS are shown in black. The Fermi level ${\mathrm{E}}_F$ is at zero.

Figure 5

Electron spin densities in codoped ${\mathrm{Mo}}_{61}{\mathrm{Co}}_2{\mathrm{CuS}}_{128}$ system. The left panel shows the positive spin density in the codoped system. The right panel shows the induced negative spin density. As seen in the figure, the majority of the positive spin density is localized on the Co atoms. In the left panel we used an isosurface of 0.05 ${\mathrm{e}/\AA }^3$, while for the right panel we used an isosurface of 0.02 ${\mathrm{e}/\AA }^3$ for clarity. The Co and Cu atoms are indicated by green and brown color, respectively.

Figure 6

Relaxed structure of ${\mathrm{Mo}}_{62}{\mathrm{Mn}}_2{\mathrm{Sb}}_2{\mathrm{S}}_{126}$. Mo, S, Mn, and Sb atoms are denoted by cyan, blue, black, and orange color, respectively.