Phase Formation and Magnetic Properties of QS-Type Ferrites with Fe2+ and Fe3+ Substitution

QS-type ferrites, having Ba2Sn2+xFe3+10.67-1.33xO22 and Ba2Sn2+xFe2+1+xFe3+10-2xO22 stoichiometries, were synthesized via powder metallurgy to map their synthesis conditions as functions of composition (x) and sintering temperature (TS). Single-phase Ba2Sn2+xFe3+10.67-1.33xO22 was achieved within the -0.2 ≤ x ≤ 0.0 range, whereas Ba2Sn2+xFe2+1+xFe3+10-2xO22 was identified as the main phase for 0.0 ≤ x ≤ 0.1. Néel temperatures (TN) near 455 K (Ba2Sn2+xFe3+10.67-1.33xO22) and 410 K (Ba2Sn2+xFe2+1+xFe3+10-2xO22) were detected through the temperature dependence of magnetization, thereby indicating distinct antiferromagnetic states. High-field magnetization measurements (Hmax = 600 kOe, T = 4.2 K) displayed a low-field antiferromagnetic response, rapid growth below 100 kOe, and high-field plateaus, from which magnetic structure models were subsequently proposed. These findings contribute to the clarification of both the phase stability and magnetic behavior of QS-type ferrites concerning Fe valence chemistry.