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

Single-phase samples of Ba2Sn2+xLi0.5+0.5xFe10.5-1.5xO22 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 μB/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.