Optical fingerprints of the electronic band reconstruction in van der Waals magnetic materials

We report a broadband study of the charge dynamics in the van der Waals (vdW) magnetic materials 2H-$M_x$TaS$_2$ ($M$ = Mn and Co), which span the onset of both long-range antiferromagnetic (AFM) and ferromagnetic (FM) order, depending on the intercalation $M$ and its concentration $x$. We discover a spectral weight ($SW$) shift from high to low energy scales for FM compositions, while reversely $SW$ is removed from low towards high spectral energies for AFM compounds. This maps the related reconstruction of the electronic band structure along the crossover from the FM to AFM order, which restores an occupation balance in the density of states between spin majority and minority bands of the intercalated 3$d$ elements.