Microwave sintered Sr1−xLaxFe12−xCoxO19 (x = 0–0.5) ferrites for use in low temperature co-fired ceramics technology

Abstract

The La3+ and Co2+ substituted Sr1−xLaxFe12−xCoxO19 (x = 0–0.5) ferrites with Bi2O3 sintering aid were prepared by microwave sintering method at a low sintering temperature of 870 °C compatible with low temperature co-fired ceramics (LTCC) systems. Detailed effect of La–Co substitution amount on their crystal structure and magnetic properties were mainly investigated. The results show that the pure M-type crystal phase is successfully obtained for the ferrites with La–Co substitution amount x not higher than 0.3. With further increased substitution amount, the multiphase structure is formed, where the non-magnetic α-Fe2O3 phase and LaCoO3 phase coexist with the M-type phase. Appropriate La–Co substitution improves the magnetic properties of the ferrites, including the saturation magnetization Ms, effective magnetic anisotropy constant Keff, magnetic anisotropy field Ha, and intrinsic coercivity Hci. Besides, the Curie temperature TC of the ferrites exhibits a rapid decrease when the La–Co substitution amount exceeds 0.3. It is suggested that the La3+–Co2+ ions can partially substitute the Sr2+–Fe3+ ions for the ferrites, leading to enhanced magnetic properties. Typically, the obtained Sr1−xLaxFe12−xCoxO19 (x = 0.2–0.3) ferrites can provide improved Ms above 64 emu/g, Ha above 1510 kA/m, and Hci above 330 kA/m as low temperature sintered M-type hexaferrites, which are promising for use in future design and realisation of self-biased circulators in LTCC systems.