The family of chiral, noncentrosymmetric, quaternary sulfides R6(TM)x(E)2Q14 (R = rare-earth metal; TM = transition metal; E = Si, Ge, Sn, Al, or Ga; and Q = S or Se) presents an exciting opportunity for exploration of their magnetic characteristics. The magnetic properties of these materials are directly influenced by the specific R and TM elements present in the sublattices. However, since the concentration of the TM is low (1 out of 23 atoms) with 50% partial occupancy, it is unclear whether and how TMs contribute to the overall magnetism of the compounds. To investigate the role of TM, two rare-earth Fe quaternary sulfide materials, R6FeSi2S14 (R = Tb, Y), were synthesized through a solid-state reaction of arc-melted R6FeSi2 precursors with sulfur, and systematic studies were conducted on polycrystalline powders and single crystals. Y6FeSi2S14 enables the exclusive study of Fe's magnetic behavior due to the nonmagnetic nature of Y3+. Tb6FeSi2S14 provides valuable insights into the interplay of 3d and 4f contributions in the presence of magnetic Tb. Magnetic measurements confirmed that both compounds exhibit a characteristic antiferromagnetic (AFM) peak. Y6FeSi2S14 showed a Néel temperature, TN, of ∼5 K, an effective magnetic moment, μeff, of 5.68 μB per Fe atom, and a negative Weiss constant, θ, of −19 K, confirming antiferromagnetic interactions of Fe magnetic moments. For Tb6FeSi2S14, TN increases with the introduction of Tb, reaching 14 K with a θ of −18 K. The derived μeff of 24.68 μB is higher than the contribution of 6 × Tb3+ ions (√6 × 9.72 = 23.81 μB) but close to the sum of the contribution of 6Tb + 1Fe. Magnetic structure refinement performed on neutron powder diffraction data indicates that the Fe moments in Y6FeSi2S14 are aligned along the [001] direction in an AFM order, which agrees with single-crystal directional magnetization measurements. When Y is replaced with Tb, the Tb moments are ordered in a noncollinear configuration in the ab-plane, with the Tb triangles stacked to form buckled honeycombs, while the Fe moments maintain their collinearity along the c-axis. Consequently, the complex nature of magnetism in R6(TM)x(E)2Q14 quaternaries is due to a superposition of contributions from R3+ and TM magnetic sublattices.
