Synthesis Conditions and Magnetic Properties for Li-Based QS-Type Hexaferrite

Abstract

  Single-phase samples of Ba₂Sn_2+xLi_0.5+0.5xFe_10.5-1.5xO₂₂ were successfully synthesized at sintering temperatures between 1100 and 1250°C within the compositional range of -0.2 ≤ x ≤ 0.4. Substitution of Li⁺ and Sn⁴⁺ for Fe³⁺ with increasing x led to an expansion of the lattice constants. Higher sintering temperatures promoted the formation of a secondary phase, BaSn₂Fe₄O₁₁, shifting the single-phase region toward lower x values. Increasing x decreased the Néel temperature, indicating weakened Fe-O-Fe superexchange interactions. Magnetic measurements at 4.2 K showed a saturation magnetization of 16 μ_B/f.u. at x = 0. A ferrimagnetic model, combined with the saturation magnetization, was used to estimate Li⁺-site occupancy. The results suggest that, with increasing x, Li⁺ occupancy at tetrahedral sites within the spinel block increases, while occupancy at octahedral sites decreases, maintaining local charge balance with the increased Sn⁴⁺ content at the Q-S block boundary. This redistribution of Li⁺ likely plays a key role in determining the material’s magnetic properties.