Consequences of magnetic ordering in chiral M n1/3Nb S2

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∼45K 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 either a short-range ferromagnetic (FM) order with a domain size of ∼250 nm along the c axis or a possible magnetic modulation with a large pitch length. The expectation of a significant Dzyaloshinskii-Moriya interaction in this chiral-structured magnet, along with the helical state discovered in isostructural Cr1/3NbS2, suggest either a long period helical state with q∼0.0025Å-1, or FM regions separated by magnetic solitons, may be responsible for the apparent small size of the FM domains. Here, the domain length along the c axis is substantially larger than the pitch length of 48 nm found for the helimagnetic state in Cr1/3NbS2. Specific-heat-capacity measurements confirm a second-order magnetic phase transition with a substantial magnetic contribution that persists to low temperature. The 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.