Tuneable anisotropy and magnetism in Sn₂Co₃S_2−xSe_x– probed by¹¹⁹Sn Mößbauer spectroscopy and DFT studies

Abstract

The half metal (HFM) Sn2Co3S2 shows a fascinating S = 1/2 magnetism. Anisotropic coupling of spins in and between Co Kagomé layers by Sn sites is now studied from the substitution effects of S by Se by systematic and local experimental and first principles data. Trends in crystal structure changes (c/a ratio) as retrieved from XRD data on the solid solution Sn2Co3S2-xSex are complemented by DFT modelling on Sn2Co3SeS and hitherto unknown Sn2Co3Se2. The relationship of crystal structure effects with changes in Curie temperatures and magnetic hysteresis is shown from susceptibility measurements. An insight into the role of the Sn sites in magnetism and bonding is gained from (119)Sn Mössbauer spectroscopic measurements. Isomer shifts, quadrupole splitting, and magnetic hyperfine fields are interpreted by DFT calculations on chemical bonding, electric field gradients (EFG), Fermi contact, and spin polarization.

Structure and Bonding of La2NiBi

“…The given picture coincides with the one given for La 2 NiSb with negatively charged Sb and positive La. It underlines the role of polarized metal–metal bonds that are also found for Laves phases and shandites . The given analysis points out the exceptional bonding situation of Ni.…”

“…Interstitial ELF maxima are also identified between the La atoms (marked by an arrow in Figure c) similar to La 2 NiSb. They are due to multi‐center bonds and can be found in intermetallic compounds like Laves phases or shandites, . The given analyses underline the strong intermetallic bonding system along the chains in La 2 NiBi.…”

“…In contrast to e.g. Ni 0 in ternary sulfides, strong Ni‐4s bands are found for La 2 BiNi in the range of –3 and –4.5 eV. Ni‐3d states mainly contribute to bands from –2.5 to –0.5 eV and to a lower degree to unoccupied states at and above the Fermi energy ( E F ).…”

Quasi-Two-Dimensional Magnetism in Co-Based Shandites

“…21,23,25,26,33) The suppressions of the ferromagnetic order by the Ni-and Fesubstitution for Co were also observed, [34][35][36] while the Sesubstitution for S causes slight reduction of T C . 30,37) The Co-based shandite is a layered compound exhibiting the ferromagnetic instability controlled by several chemical substitutions and is a good candidate to investigate novel phenomena due to the Q2D electronic state.…”

Half antiperovskites VII – DFT modelling of shandites that are isoelectronic to Co3Sn2S2

“…[9] The position and topology of these bands is determined by CoÀ Co, but also by CoÀ S and CoÀ Sn-bands within Sn 4 S 2 polyhedra as studied by the electron localization function (ELF). [36,37] According to first results on partial M site substitution by Ni [38] simultaneous substitution of A site atoms directs a way to tune band topology.…”