Fe and Cr co-intercalation in $2\text{H-Nb}{\mathrm{S}}_2$ single crystals for realization of perpendicular magnetic anisotropy and large anomalous Hall effect

Recently, many interesting magnetic and electrical properties have been demonstrated in transition-metal intercalated $2\text{H-Nb}{\mathrm{S}}_2/\mathrm{Ta}{\mathrm{S}}_2$ layered single crystals. In this work, single crystals of Cr and Fe co-intercalated $2\text{H-Nb}{\mathrm{S}}_2$, with the compositions of ${\left({\mathrm{Cr}}_{1–x}{\mathrm{Fe}}_x\right)}_{1/3}\mathrm{Nb}{\mathrm{S}}_2 \left(x=0.0–1.0\right)$, are successfully grown and their magnetic and transport properties are systematically studied. With increasing Fe content, the magnetic transition temperature continually decreases from 117 to 37 K, and the magnetic coupling transforms from ferromagnetic to antiferromagnetic. Importantly, a rotation of the magnetic easy axis occurs in this process, with perpendicular magnetocrystalline anisotropy and considerable coercive field achieved in the $x=0.13–0.66$ compounds. Both $x=0.33$ and $x=0.50$ exhibit relatively low carrier concentration, stable anomalous Hall effect, and butterfly-shape magnetoresistance. Notably, large anomalous Hall conductivity is identified in $x=0.50$, whose origin is discussed from the calculated electronic structures. The realization of perpendicular anisotropy and large anomalous Hall conductivity in this two-dimensional ferromagnetic system can facilitate their future application in spintronic devices.

Figure 1

(a) Crystal structure of bulk ${\mathrm{M}}_{1/3}\mathrm{Nb}{\mathrm{S}}_2$ (($M=\mathrm{Cr}$ or/and Fe). Blue, green, and yellow balls represent Cr or Fe, Nb, and S atoms, respectively. (b) XRD patterns of ${\left({\mathrm{Cr}}_{1–x}{\mathrm{Fe}}_x\right)}_{1/3}\mathrm{Nb}{\mathrm{S}}_2$ single-crystal thin plates, along with (008) enlarged diffraction peaks. (c) The morphology and elemental distribution of sample $x=0.50$ single crystal scanned by SEM. (d) The $c$-lattice parameters for ${\left({\mathrm{Cr}}_{1–x}{\mathrm{Fe}}_x\right)}_{1/3}\mathrm{Nb}{\mathrm{S}}_2$ plotted with Fe doping content. Inset: Optical image of ${\left({\mathrm{Cr}}_{1–x}{\mathrm{Fe}}_x\right)}_{1/3}\mathrm{Nb}{\mathrm{S}}_2$ single crystals.

Figure 2

[(a)–(e)] Temperature-dependent magnetization $M\text{−}T$ curves of ${\left({\mathrm{Cr}}_{1-x}{\mathrm{Fe}}_x\right)}_{1/3}\mathrm{Nb}{\mathrm{S}}_2 \left(0.0\le x\le 1.0\right)$ measured in field-cooling process with ${\mu }_{0}H=0.05$ T for $H\perp ab$ (solid symbols) and $H\parallel ab$ (open symbols), respectively. (f) Doping-temperature magnetic phase diagram of ${\left({\mathrm{Cr}}_{1-x}{\mathrm{Fe}}_x\right)}_{1/3}\mathrm{Nb}{\mathrm{S}}_2$.

Figure 3

(a) $M\text{−}H$ curves along $H\perp ab$ and $H\parallel ab$ for various compositions of $0.0\le x\le 0.66$ at $T=10$ K. (b) The extracted remanence $\left(M_r\right)$ and coercive field $\left(H_c\right)$ values of ${\left({\mathrm{Cr}}_{1-x}{\mathrm{Fe}}_x\right)}_{1/3}\mathrm{Nb}{\mathrm{S}}_2$. (c) $M\text{−}H$ curves at a dense magnetic field variation for three components, $x=0.0$ (at 10 K), 0.13 (at 100 K), and 0.50 (at 10 K). (d) $M\text{−}H$ curves of $x=0.13$ along $H\perp ab$ and $H\parallel ab$ at different temperatures (10, 30, 50, 100, and 150 K).

Figure 4

[(a), (b)] Hall resistivity of $x=0.33$ and 0.50 with $H\perp ab$ at different temperatures. (c) ${\sigma }_{xy}^A$ vs $T$ plot for samples in this work and other similar systems [25, 30, 47, 48, 49]. (d) $n$ vs $T$ plot for samples in this work and other systems [36, 48, 50, 51, 52, 53]. [(e), (f)] MR for samples of $x=0.33$ and 0.50 with $H\perp ab$ at different temperatures.

Figure 5

[(a)–(c)] Spin and atomic resolved density of states (DOS) for ferromagnetic ${\mathrm{Cr}}_{1/3}\mathrm{Nb}{\mathrm{S}}_2, {\left({\mathrm{Cr}}_{0.50}{\mathrm{Fe}}_{0.50}\right)}_{1/3}\mathrm{Nb}{\mathrm{S}}_2$, and antiferromagnetic ${\mathrm{Fe}}_{1/3}\mathrm{Nb}{\mathrm{S}}_2$, respectively. The red and blue areas correspond to total DOS in spin-up and spin-down directions, respectively; the gray and green areas correspond to the partial DOS of Cr and Fe atoms, respectively. [(d)–(f)] are their corresponding band structures. As ${\mathrm{Fe}}_{1/3}\mathrm{Nb}{\mathrm{S}}_2$ is antiferromagnetic, the spin-up band is superposed with that of spin down.