Antiferromagnetism and the emergence of frustration in saw-tooth lattice chalcogenide olivines Mn\(_2\)SiS\(_{4-x}\)Se\(_x\) (\(x\) = 0 \(\textendash\) 4)

• Published in: arXiv.org
• Main Authors: Nhalil, H, Baral, R, Khamala, B O, Cosio, A, Singamaneni, S R, Fitta, M, Antonio, D, Gofryk, K, Zope, R R, Baruah, T, Saparov, B, Nair, H S
• Format: Paper
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 03.05.2019
• Subjects: Antiferromagnetism; Chalcogenides; Critical field (superconductivity); Density functional theory; Ferromagnetism; Magnetic anomalies; Magnetic properties; Magnetism; Magnetization; Mathematical analysis; Olivine; Phase transitions; Selenium; Short range order; Specific heat; Thermal conductivity; Transition temperature; Variations
• ISSN: 2331-8422

The magnetism in the saw-tooth lattice of Mn in the olivine chalcogenides, Mn\(_2\)SiS\(_{4-x}\)Se\(_x\) (\(x\) = 1\(\textendash\)4) is studied in detail by analyzing their magnetization, specific heat and thermal conductivity properties and complemented with density functional theory calculations. The air-stable chalcogenides are antiferromagnets and show a linear trend in the transition temperature, \(T_N\) as a function of Se-content (\(x\)) which shows a decrease from \(T_N \approx\) 86~K for {\mss} to 66~K for {\msse}. Additional new magnetic anomalies are revealed at low temperatures for all the compositions. Magnetization irreversibilities are also observed as a function of \(x\). The specific heat and the magnetic entropy indicate the presence of short-range spin fluctuations in Mn\(_2\)SiS\(_{4-x}\)Se\(_x\). A spin-flop antiferromagnetic phase transition in the presence of applied magnetic field is present in Mn\(_2\)SiS\(_{4-x}\)Se\(_x\), where the critical field for the spin flop increases from \(x\) = 0 towards 4 in a non-linear fashion. Density functional theory calculations show that an overall antiferromagnetic structure with ferromagnetic coupling of the spins in the \(ab\)-plane minimizes the total energy. The band structures calculated for \mss\ and \msse\ reveal features near the band edges similar to those reported for Fe-based olivines suggested as thermoelectrics; however the experimentally determined thermal transport data do not support superior thermoelectric features. The transition from long-range magnetic order in \mss\ to short-range order and spin fluctuations in \msse\ is explained using the variation of the Mn-Mn distances in the triangle units that constitutes the saw-tooth lattice upon progressive replacement of sulphur with selenium.