Very large magnetoresistance in ${\mathrm{Fe}}_{0.28}{\mathrm{TaS}}_2$ single crystals

Magnetic moments intercalated into layered transition metal dichalcogenides are an excellent system for investigating the rich physics associated with magnetic ordering in a strongly anisotropic, strong spin-orbit coupling environment. We examine electronic transport and magnetization in ${\mathrm{Fe}}_{0.28}{\mathrm{TaS}}_2$, a highly anisotropic ferromagnet with a Curie temperature $T_{\mathrm{C}}\sim 68.8$ K. We find anomalous Hall data confirming a dominance of spin-orbit coupling in the magnetotransport properties of this material, and a remarkably large field-perpendicular-to-plane magnetoresistance (MR) exceeding 60% at 2 K, much larger than the typical MR for bulk metals, and comparable to state-of-the-art giant MR in thin film heterostructures, and smaller only than colossal MR in Mn perovskites or high mobility semiconductors. Even within the ${\mathrm{Fe}}_x{\mathrm{TaS}}_2$ series, for the current $x=0.28$ single crystals the MR is nearly $100\times$ higher than that found previously in the commensurate compound ${\mathrm{Fe}}_{0.25}{\mathrm{TaS}}_2$. After considering alternatives, we argue that the large MR arises from spin-disorder scattering in the strong spin-orbit coupling environment, and suggest that this can be a design principle for materials with large MR.

Figure 1

(a) ZFC (solid symbols) and FC (open symbols) temperature-dependent magnetic susceptibility of a bulk sample measure in an applied field $H=0.1$ T, $H\parallel c$. Inset: The Curie temperature $T_{\mathrm{C}}$ is determined from the minimum in $dM/dT$ (solid symbols) and an inflection point in $d\rho /dT$ (line). (b) Temperature-dependent resistivity of both bulk (open symbols) and exfoliated (solid line) samples.

Figure 2

$H\parallel c$ (solid symbols) field-dependent magnetization $M\left(H\right)$ data at various temperatures, together with the $T=1.8$ K, $H\parallel ab$ (open symbols) isotherm. For clarity, the two close isotherms ($H\parallel c$ for $T=200$ K and $H\parallel ab$ for $T=1.8$ K) are only shown for $H<0$ and $H>0$, respectively.

Figure 3

MR of (a) bulk and (b) exfoliated samples at selected temperatures for $H\parallel c$, and the current $i \parallel ab$.

Figure 4

Anomalous Hall resistivity for (a) bulk and (b) exfoliated samples at selected temperatures for $H \parallel c$, and the current $i \parallel ab$.

Figure 5

Angle-dependent measurements on an exfoliated sample of the longitudinal MR (left) and Hall resistivity (right) as a function of magnetic field $H$, for $H\parallel c$, and the current $i \parallel ab$. (a) Data at $T=30$ K for various field orientations relative to the $c$ axis. (b) Comparison of $H\parallel c$ and $H\parallel ab$ data for $T=10$ and 30 K.

Figure 6

SAED pattern of ${\mathrm{Fe}}_{0.28}{\mathrm{TaS}}_2$ crystal showing two concentric hexagonal sets of spots: the main structure (bright, large circles) and superlattice reflections (faint, small circles). The superstructure unit cell (small hexagonal cell) appears rotated by ${90}^{\circ }$ from the main structure unit cell (large hexagonal cell).

Figure 7

Determination of the switching field $H_S$ for (a) bulk and (b) exfoliated samples from $M\left(H\right)$ (blue), MR (black), and anomalous Hall resistivity (red). The vertical dashed line marks the switching field $H_S$, as determined from the field values where $M\left(H\right)$ and ${\rho }_{xy}$ cross $H=0$, and where the fastest drop in $\Delta \rho /{\rho }_0$ occurred.

Figure 8

Comparison of $H_S$ and magnetoresistivity peak height values as a function of temperature for bulk (solid symbols) and exfoliated (open symbols) samples. $H_S$ increased monotonically with decreasing temperature, while the magnetoresistivity peak height increased with decreasing temperature until 4 K, and then decreased at lower temperatures. Inset: Image of a typical bulk sample (left), and false-color SEM image of a typical exfoliated sample with metal contacts (right).