Stabilization of antiferromagnetism in 1T-${\mathrm{Fe}}_{0.05}{\mathrm{TaS}}_2$

1T-${\mathrm{TaS}}_2$ is a prototypical charge-density-wave system with a Mott insulating ground state. Usually, a Mott insulator is accompanied by an antiferromagnetic state. However, the antiferromagnetic order had never been observed in 1T-${\mathrm{TaS}}_2$. Here, we report the stabilization of the antiferromagnetic order by the intercalation of a small amount of Fe into the van der Waals gap of 1T-${\mathrm{TaS}}_2$, i.e., forming 1T-${\mathrm{Fe}}_{0.05}{\mathrm{TaS}}_2$. Upon cooling from 300 K, the electrical resistivity increases with a decreasing temperature before reaching a maximum value at around 15 K, which is close to the Néel temperature determined from our magnetic susceptibility measurement. The antiferromagnetic state can be fully suppressed when the sample thickness is reduced, indicating that the antiferromagnetic order in ${\mathrm{Fe}}_{0.05}{\mathrm{TaS}}_2$ has a non-negligible three-dimensional character. For the bulk ${\mathrm{Fe}}_{0.05}{\mathrm{TaS}}_2$, a comparison of our high pressure electrical transport data with that of 1T-${\mathrm{TaS}}_2$ indicates that, at ambient pressure, ${\mathrm{Fe}}_{0.05}{\mathrm{TaS}}_2$ is in the nearly commensurate charge-density-wave phase near the border of the Mott insulating state. The temperature-pressure phase diagram thus reveals an interesting decoupling of the antiferromagnetism from the Mott insulating state.

Figure 1

(a) Temperature dependence of the electrical resistivity in ${\mathrm{Fe}}_{0.05}{\mathrm{TaS}}_2$ at ambient pressure and zero field. The vertical arrow denotes the peak temperature of 15.7 K. (b) Temperature dependence of the magnetic susceptibility in ${\mathrm{Fe}}_{0.05}{\mathrm{TaS}}_2$. The data were collected with 50 Oe applied along the $c$ axis. The inset shows the same data set plotted as the inverse of the magnetic susceptibility against the temperature. The dotted line is the linear fit of the data from 9.2 K to 50 K. (c) Temperature dependence of the electrical resistivity in ${\mathrm{Fe}}_{0.05}{\mathrm{TaS}}_2$ under pressure. The data were collected on cooling. The vertical arrow indicates $T_{\mathrm{NCCDW}}$ at 13.9 kbar, defined as the temperature at which $d\rho /dT$ is a local minimum. The inset shows the low temperature region of $\rho \left(T\right)$ at 17.3 kbar, collected at 0 T, 1 T, and 2 T. The field is along the $c$ axis. $T_{c,\mathrm{onset}}$ is defined as the temperature below which $\rho \left(T\right)$ drops substantially (see the dashed vertical arrow).

Figure 2

Calculated Band 20 Fermi surface of the undistorted 1T-${\mathrm{TaS}}_2$ (a) at ambient pressure, (c) at 20 kbar, and (d) when the Fermi energy is shifted upward by 0.01 Ry relative to the band structure at ambient pressure, i.e., $E_F=E_F(p=0)+0.01$ Ry. The first Brillouin zone and the high symmetry points of 1T-${\mathrm{TaS}}_2$ are shown in (b), and $a^{*}$, $b^{*}$ and $c^{*}$ are the basis vectors of the reciprocal lattice. $c^{*}$ is parallel to the $k_z$ axis.

Figure 3

Temperature dependence of the electrical resistivity in ${\mathrm{Fe}}_{0.05}{\mathrm{TaS}}_2$ flakes with different thicknesses ranging from 9 nm to 131 nm. Note the logarithmic scale for the temperature axis. Inset: the low temperature part of the resistivity in the ${\mathrm{Fe}}_{0.05}{\mathrm{TaS}}_2$ flake with the thickness of 131 nm, where a peak similar to the data on the bulk sample is observed, as indicated by the arrow.

Figure 4

Temperature-pressure phase diagram for 1T-${\mathrm{TaS}}_2$ (bottom axis) and 1T-${\mathrm{Fe}}_{0.05}{\mathrm{TaS}}_2$ (top axis). The top axis is offset by 13 kbar relative to the bottom axis. The open symbols are from Ref. [3], and the closed symbols are data from this work. “I” denotes the CCDW and the Mott state; “II” denotes the NCCDW state.

Figure 5

(a) Scanning electron microscope image of Crystal 1. The white rectangles are the spots we chose to perform the measurements. (b) Energy-dispersive x-ray spectroscopy result of “Spectrum 1” for ${\mathrm{Fe}}_{0.05}{\mathrm{TaS}}_2$ (Crystal 1).