Magnetic structures and excitations in sawtooth olivine chalcogenides Mn2SiX4 (X = S, Se)

Hector C. Mandujano, Melaku Sisay Tafere, Naveen Kumar Chogondahalli Muniraju, Tielyr D. Creason, Timothy M. McWhorter, Krzysztof Gofryk, Thomas W. Heitmann, Qiang Zhang, Bayram Saparov, Harikrishnan S. Nair

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Abstract

The Mn lattice in olivine chalcogenide Mn2SiX4 (X = S, Se) compounds forms a sawtooth, which is of special interest in magnetism owing to the possibility of realizing flat bands in magnon spectra, a key component in magnonics. In this work, we investigate the Mn2SiX4 olivines using magnetic susceptibility, and X-ray and neutron diffraction. We have determined the average and local crystal structures of Mn2SiS4 and Mn2SiSe4 using synchrotron X-ray, neutron diffraction, and X-ray total scattering data followed by Rietveld and pair distribution function analyses. It is found from the pair distribution function analysis that the Mn triangle that constitutes the sawtooth is isosceles in Mn2SiS4 and Mn2SiSe4. The temperature evolution of magnetic susceptibility of Mn2SiS4 and Mn2SiSe4 shows anomalies below 83 K and 70 K, respectively, associated with magnetic ordering. From the neutron powder diffraction measurements the magnetic space groups of Mn2SiS4 and Mn2SiSe4 are found to be Pnma and Pnm′a′, respectively. We find that the Mn spins adopt a ferromagnetic alignment on the sawtooth in both Mn2SiS4 and Mn2SiSe4 but along different crystallographic directions for the S and the Se compounds. From the temperature evolution of Mn magnetic moments obtained from refining neutron diffraction data, the transition temperatures are accurately determined as TN(S) = 83(2) K and TN(Se) = 70.0(5) K. Broad diffuse magnetic peaks are observed in both the compounds, and are prominently seen close to TN, suggesting the presence of a short-range magnetic order. The magnetic excitations studied using inelastic neutron scattering reveal a magnon excitation with an energy corresponding to approximately 4.5 meV in both S and Se compounds. Spin correlations are observed to persist up to 125 K much above the ordering temperature and we suggest the possibility of short-range spin correlations responsible for this.

Original languageEnglish
Pages (from-to)5652-5662
Number of pages11
JournalDalton Transactions
Volume52
Issue number17
DOIs
StatePublished - Mar 21 2023

Funding

The use of the Advanced Photon Source at the Argonne National Laboratory was supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. HCM, MST and HSN would like to acknowledge the help of 11 BM and 11 ID B beamline scientists. This work has been supported in part by the Croatian Science Foundation under the Project No. IP-2020-02-9666. CMNK acknowledges support from the project Cryogenic Centre at the Institute of Physics - KaCIF, co-financed by the Croatian Government and the European Union through the European Regional Development Fund - Competitiveness and Cohesion Operational Programme (Grant No. KK.01.1.1.02.0012). Part of this research used resources at Spallation Neutron Source, User Facility operated by the Oak Ridge National Laboratory. KG acknowledges support from the INL Laboratory Directed Research & Development (LDRD) Program under DOE Idaho Operations Office Contract DE-AC07-05ID14517. The use of the Advanced Photon Source at the Argonne National Laboratory was supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. HCM, MST and HSN would like to acknowledge the help of 11 BM and 11 ID B beamline scientists. This work has been supported in part by the Croatian Science Foundation under the Project No. IP-2020-02-9666. CMNK acknowledges support from the project Cryogenic Centre at the Institute of Physics – KaCIF, co-financed by the Croatian Government and the European Union through the European Regional Development Fund – Competitiveness and Cohesion Operational Programme (Grant No. KK.01.1.1.02.0012). Part of this research used resources at Spallation Neutron Source, User Facility operated by the Oak Ridge National Laboratory. KG acknowledges support from the INL Laboratory Directed Research & Development (LDRD) Program under DOE Idaho Operations Office Contract DE-AC07-05ID14517.

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