Experimental confirmation of the magnetic ordering transition induced by an electronic structure change in the metallic triangular antiferromagnet Co${}_{1\mathrm{/}3}$TaS${}_2$

We report ARPES studies combined with DFT+DMFT calculations to confirm that the magnetic ordering vector transition from $\mathbf{\text{Q}}$=(1/2,0,0) to $\mathbf{\text{Q}}$=(1/3,0,0) in the metallic triangular antiferromagnets Co${}_{1\mathrm{/}3\pm \epsilon }$TaS${}_2$ ($\epsilon \approx$0.007) is induced by the electronic structure change in the system. The ARPES-measured Fermi surface (FS) maps of Co${}_{0.325}$TaS${}_2$ show two hexagonal and one circular hole-like FSs around $\mathrm{\Gamma }$, which matches well with the triple-$\mathbf{\text{Q}}$ state by taking into account the contribution of nesting vectors occurring between Co 3$d$ and Ta 5$d$ orbitals. In the case of Co${}_{0.340}$TaS${}_2$, a new electron pocket around K appears and the FS geometry changes as a result of the correlation effect of Co${}_4$S${}_{18}$ tripods forming in the system. The magnetic susceptibility calculations based on the charge-self-consistent DFT+DMFT band structures and the random phase approximation indicate that the most stable magnetic ordering vector (1/2,0,0) split into (1/6,0,0) and (1/2,0,0), which is consistent with the magnetic phase transition around $x$=1/3 in Co${}_x$TaS${}_2$.