Consequences of magnetic ordering in chiral $\mathrm{M}{\mathrm{n}}_{1/3}\mathrm{Nb}{\mathrm{S}}_2$

Journal Article · 11 November 2019 · Physical Review B

DOI: https://doi.org/10.1103/PhysRevB.100.184413 · OSTI ID:1632095

Karna, Sunil K. ^[1]; Womack, F N. ^[1]; Chapai, R ^[1]; Young, D. P. ^[1]; Marshall, M ^[1]; Xie, Weiwei ^[1]; Graf, D. ^[2]; Wu, Yan  ^[3]; Cao, Huibo  ^[3]; Debeer-Schmitt, Lisa M.  ^[3]; Adams, P W. ^[1]; Di tusa, John ^[1]

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1. Louisiana State Univ., Baton Rouge, LA (United States)
2. Florida State Univ., Tallahassee, FL (United States)
3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

We have investigated here the structural, magnetic, thermodynamic, and charge-transport properties of $\mathrm{M}{\mathrm{n}}_{1/3}\mathrm{Nb}{\mathrm{S}}_2$ single crystals through x-ray and neutron diffraction, magnetization, specific heat, magnetoresistance, and Hall-effect measurements. $\mathrm{M}{\mathrm{n}}_{1/3}\mathrm{Nb}{\mathrm{S}}_2$ displays a magnetic transition at $T_C~45\mathrm{K}$ with highly anisotropic behavior expected for a hexagonal-structured material. Below $T_C$, 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 $\mathrm{C}{\mathrm{r}}_{1/3}\mathrm{Nb}{\mathrm{S}}_2$, suggest either a long period helical state with $q~0.0025{\AA }^{-1}$, 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 $\mathrm{C}{\mathrm{r}}_{1/3}\mathrm{Nb}{\mathrm{S}}_2$. 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 determinations signify a more complex magnetic structure both at zero and finite fields for $\mathrm{M}{\mathrm{n}}_{1/3}\mathrm{Nb}{\mathrm{S}}_2$ than for the well-investigated $\mathrm{C}{\mathrm{r}}_{1/3}\mathrm{Nb}{\mathrm{S}}_2$.

• Research Organization: Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States); Louisiana State University Baton Rouge, LA (United States); Louisiana State Univ., Baton Rouge, LA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES); National Science Foundation (NSF)
• Grant/Contract Number: AC05-00OR22725; SC0012432; FG02-07ER46420; DMR-1644779
• OSTI ID: 1632095
• Alternate ID(s): OSTI ID: 1632687; OSTI ID: 1673162
• Journal Information: Physical Review B, Vol. 100, Issue 18; ISSN 2469-9950
• Publisher: American Physical Society (APS)Copyright Statement
• Country of Publication: United States
• Language: English