Competing Localized-Itinerant Magnetism Evidenced by Critical Behavior in the FexTi2S4 Heideite Sulfides

Abstract

We report the critical behavior of the Fe_xTi₂S₄ (x = 0.24, 0.42) intercalated Heideite sulfides in the vicinity of their second-order magnetic phase transition. Several methods including the modified Arrott plot, Widom scaling law, and the critical isotherm analysis reliably yield critical exponents β = 1.105/0.442, γ = 0.913/1.042, and δ = 1.826/3.357, in agreement with the scaling hypothesis, although slightly deviating from the conventional theoretical values. Using the renormalization group theory analysis, we conclude that the exchange distance J(r) and the correlation length critical exponent ν indicate that increasing Fe content induces a transition from localized spin interactions, described by the mean-field model, to an itinerant-electron 3D Heisenberg-like model near T_C. These features reveal a coupling between short- and long-range magnetic interactions, which are responsible for the unconventional critical behavior in Fe_xTi₂S₄. Our results provide valuable insights into the magnetic nature and offer tuning mechanisms in Fe_xTi₂S₄ intercalated sulfides.