Disentangling electronic, lattice, and spin dynamics in the chiral helimagnet Cr1/3Nb S2

We investigate the static and ultrafast magneto-optical response of the hexagonal chiral helimagnet Cr1/3NbS2 above and below the helimagnetic ordering temperature. The presence of a magnetic easy plane contained within the crystallographic ab plane is confirmed, while degenerate optical pump-probe experiments reveal significant differences in the dynamic between the parent, NbS2, and Cr-intercalated compounds. Time-resolved magneto-optical Kerr effect measurements show a two-step demagnetization process, where an initial, subpicosecond relaxation and subsequent buildup (τ>50ps) in the demagnetization dynamic scale similarly with increasing pump fluence. Despite theoretical evidence for partial gapping of the minority spin channel, suggestive of possible half-metallicity in Cr1/3NbS2, such a long demagnetization dynamic likely results from spin-lattice relaxation as opposed to minority state blocking. However, comparison of the two-step demagnetization process in Cr1/3NbS2 with other 3d intercalated transition metal dichalcogenides reveals a behavior that is unexpected from conventional spin-lattice relaxation, and may be attributed to the complicated interaction of local moments with itinerant electrons in this material system.