Controlling Ferromagnetic Easy Axis in a Layered ${\mathrm{MoS}}_2$ Single Crystal

We report the effective methods to induce weak ferromagnetism in pristine ${\mathrm{MoS}}_2$ persisting up to room temperature with the improved transport property, which would lead to new spintronics devices. The hydrogenation of ${\mathrm{MoS}}_2$ by heating at $300°\mathrm{C}$ for 1 h leads to the easy axis out of plane, while the irradiation of proton with a dose of $1\times {10}^{13}\mathrm{P}/{\mathrm{cm}}^2$ leads to the easy axis in plane. The theoretical modeling supports such magnetic easy axes.

Figure 1

dc magnetization (in units of $1\mathrm{emu}={10}^{-3}{\mathrm{Am}}^2$) between 2 and 300 K with the application of an external magnetic field (H) of 10 kOe ($1\mathrm{Oe}={10}^3/4\pi {\mathrm{Am}}^{-1}$) parallel (a), (c) and perpendicular (b), (d) to the basal plane ($ab$ direction) of samples. ZFC (solid symbols) and FC (open symbols) indicate the zero-field-cooled and field-cooled modes, respectively. (Hydrogenation $Ha$: $200°\mathrm{C}$, $Hb$: $300°\mathrm{C}$, $Hc$: $400°\mathrm{C}$, Proton irradiation $Pa$: ${10}^{13}\mathrm{P}/{\mathrm{cm}}^2$, $Pb$: ${10}^{14}\mathrm{P}/{\mathrm{cm}}^2$).

Figure 2

Magnetic hysteresis loops at room temperature (300 K) in the presence of applied magnetic field H parallel (a), (c) and perpendicular (b), (d) to the hydrogenated (a), (b) and proton irradiated (c), (d) samples, respectively. Note that the diamagnetic background of the pristine ${\mathrm{MoS}}_2$ was not subtracted.

Figure 3

Images of AFM and MFM. Top panels correspond to the images of atomic force microscopy for (a) the pristine ${\mathrm{MoS}}_2$, hydrogenated at (b) $200°\mathrm{C}$ and (c) $300°\mathrm{C}$, and (d) proton irradiated at the dose of Pa ($1\times {10}^{13}\mathrm{P}/{\mathrm{cm}}^2$). The scan areas are $20\times 20\mu {\mathrm{m}}^2$. Center and bottom panels are the corresponding images of the magnetic force microscope at the distances of 30 (center) and 80 nm (bottom) between the tip and sample surface, respectively.

Figure 4

(a), (b) Resistivity ($\rho$, left axis) and carrier concentration ($n_e$, right axis) as a function of temperature (75–350 K). (c) The relation of the saturated magnetization $M_{\mathrm{S}}$ in the direction of both in plane and out of plane with $n_e$ derived from the Hall measurements at RT. Closed (open) symbols correspond to left (right) axis.

Figure 5

Top views of the isosurface plot of the spin density for ${\mathrm{MoS}}_2$ vacancy (a) and H-adsorption (b). The calculated hexagonal $4\times 4$ supercell of $1\mathrm{L}\mathrm{\text{−}}{\mathrm{MoS}}_2$ is denoted with the black line, and the blue isosurface ($\mathrm{\text{isosurface value}}=0.005e/\mathrm{a}.\mathrm{u}{.}^3$) represents the spin density. The red, yellow, and black balls represent Mo, S, and H atoms, respectively.