Effect of La–CO substitution on the crystal structure and magnetic properties of low temperature sintered Sr1−xLaxFe12−xCoxO19 (x=0–0.5) ferrites

• Low temperature sintered magnetic properties are improved by La-Co substitution.
• La3+–Co2+ ions partially substitute the Sr2+–Fe3+ ions at low sintering temperatures.
• Substituted ferrites provide Ms>62 emu/g, Ha>1400 kA/m, and Hci>320 kA/m.

The La–Co substituted Sr1−xLaxFe12−xCoxO19 (x=0–0.5) ferrites with appropriate Bi2O3 additive were prepared at a low sintering temperature of 890 °C compatible with LTCC (low temperature co-fired ceramics) systems, and the effect of La–Co substitution on their crystal structure and magnetic properties was investigated. The results show that the pure M-type phase is successfully obtained when the La–Co substitution amount x does not exceed 0.3. However, the single M-type phase structure transforms to multiphase structure with further increased x, where the α-Fe2O3 phase and La2O3 phase coexist with the M-type phase. Moreover, the saturation magnetization Ms, magnetic anisotropy field Ha, intrinsic coercivity Hci, and Curie temperature TC of the ferrites depend on the La–Co substitution amount strongly, which are suggested to be determined by the partially substitution of La3+–Co2+ ions for Sr2+–Fe3+ ions with x not higher than 0.3. It is found that the obtained Sr1−xLaxFe12−xCoxO19 (x=0.2 and 0.3) ferrites can provide improved magnetic properties (Ms>62 emu/g, Ha>1400 kA/m, and Hci>320 kA/m) as low temperature sintered M-type hexaferrites for microwave LTCC applications.