Abstract
The magnetism in the sawtooth lattice of Mn in the olivine chalcogenides, Mn2SiS4-xSex (x=1-4), 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 TN as a function of Se content (x), which shows a decrease from TN≈86K for Mn2SiS4 to 66 K for Mn2SiSe4. Additional magnetic anomalies are revealed at low temperatures for all the compositions. Magnetization irreversibilities are observed as a function of x. The specific heat and the magnetic entropy indicate the presence of short-range spin fluctuations in Mn2SiS4-xSex. A spin-flop antiferromagnetic phase transition in the presence of applied magnetic field is present in Mn2SiS4-xSex, where the critical field for the spin flop increases from x=0 towards 4 in a nonlinear 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 Mn2SiS4 and Mn2SiSe4 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 Mn2SiS4 to short-range order and spin fluctuations in Mn2SiSe4 is explained using the variation of the Mn-Mn distances in the triangle units that constitutes the sawtooth lattice upon progressive replacement of sulfur with selenium. Overall, the results presented here point towards the role played by magnetic anisotropy and geometric frustration in the antiferromagnetic state of the sawtooth olivines.
| Original language | English |
|---|---|
| Article number | 184434 |
| Journal | Physical Review B |
| Volume | 99 |
| Issue number | 18 |
| DOIs | |
| State | Published - May 24 2019 |
| Externally published | Yes |
Funding
H.S.N. acknowledges the UTEP start-up fund and UT Rising-STAR in supporting this work. B.S. acknowledges the financial support for this work provided by the University of Oklahoma start-up funds. D.A. and K.G. acknowledge support from INL's LDRD and DOE's (Basic Energy Science) Early Career Research Programs, respectively. R.R.Z. and T.B. acknowledge support by Department of Energy Basic Energy Science through Grants No. DE-SC0002168 and No. DE-SC0006818. Support for computational time by the NSF's XSEDE project through Grant No. TG-DMR090071 is gratefully acknowledged. A.C. and S.R.S. acknowledge the University of Texas at El Paso (UTEP) start-up fund and the NSF-PREM program (DMR-1205302). The part of the paper prepared by S.R.S. and A.C. is funded under Award No. 31310018M0019 from UTEP and the Nuclear Regulatory Commission. The statements, findings, conclusions, and recommendations are those of the author(s) and do not necessarily reflect the views of UTEP or the US Nuclear Regulatory Commission.