Disentangling Electronic, Lattice and Spin Dynamics in the Chiral Helimagnet Cr1/3NbS2

TL;DR

This study explores the static and ultrafast magneto-optical responses of the chiral helimagnet Cr1/3NbS2, revealing complex spin, lattice, and electronic dynamics and challenging conventional understanding of demagnetization processes.

Contribution

It provides new insights into the ultrafast spin dynamics and demagnetization mechanisms in Cr1/3NbS2, highlighting the interplay of local moments and itinerant electrons.

Findings

Two-step demagnetization process observed with sub-ps and >50 ps timescales.

Presence of magnetic easy plane within the ab-plane.

Unexpected demagnetization behavior compared to other transition metal dichalcogenides.

Abstract

We investigate the static and ultrafast magneto-optical response of the hexagonal chiral helimagnet $Cr_{1/3}NbS_{2}$ 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, $NbS_{2}$, and Cr-intercalated compounds. Time resolved magneto-optical Kerr effect measurements show a two-step demagnetization process, where an initial, sub-ps relaxation and subsequent buildup ($\tau > 50$ ps) 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 $Cr_{1/3}NbS_{2}$, 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 $Cr_{1/3}NbS_{2}$ 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.