Observation of a mesoscopic magnetic modulation in chiral Mn1/3NbS2

TL;DR

This study reveals a mesoscopic magnetic modulation in Mn1/3NbS2, showing helimagnetism with a long pitch and complex magnetic behavior at low temperatures, expanding understanding of magnetic structures in chiral layered materials.

Contribution

First detailed investigation of the magnetic structure and excitations in Mn1/3NbS2, highlighting its complex magnetic order and differences from similar compounds.

Findings

Helimagnetic order with a long pitch (~250 nm) along the c-axis.

Presence of low-lying magnetic excitations linked to topological modes.

Complex magnetic behavior emerging below 20 K.

Abstract

We have investigated the structural, magnetic, thermodynamic, and charge transport properties of Mn1/3NbS2 single crystals through x-ray and neutron diffraction, magnetization, specific heat, magnetoresistance, and Hall effect measurements. Mn1/3NbS2 displays a magnetic transition at TC ~ 45 K with highly anisotropic behavior expected for a hexagonal structured material. Below TC, neutron diffraction reveals increased scattering near the structural Bragg peaks having a wider Q-dependence along the c-axis than the nuclear Bragg peaks. This indicates helimagnetism with a long pitch length of ~250 nm (or a wavevector q~0.0025 {\AA}-1) along the c-axis. This q is substantially smaller than that found for the helimagnetic state in isostructural Cr1/3NbS2 (0.015 {\AA}-1). Specific heat capacity measurements confirm a second-order magnetic phase transition with a substantial magnetic contribution that persists to low temperature. The large low-temperature specific heat capacity is consistent with a large density of low-lying magnetic excitations that are likely associated with topologically interesting magnetic modes. Changes to the magnetoresistance, the magnetization, and the magnetic neutron diffraction, which become more apparent below 20 K, imply a modification in the character of the magnetic ordering corresponding to the magnetic contribution to the specific heat capacity. These observations signify a more complex magnetic structure both at zero and finite fields for Mn1/3NbS2 than for the well-investigated Cr1/3NbS2.