Effect of La–Co substitution on the crystal structure and magnetic properties of hot press sintered Sr1−xLaxFe12−xCoxO19 (x=0−0.5) ferrites for use in LTCC technology

• La3+–Co2+ ions partially substitute the Sr2+–Fe3+ ions at low sintering temperatures.
• Low temperature sintering properties are improved by La–Co substitution.
• Substituted ferrite sintered at 870 °C provides Ms of 65.9 emu/g and Hci of 4066.7 Oe.

The La3+ and Co2+ substituted Sr1−xLaxFe12−xCoxO19 (x=0−0.5) ferrites with Bi2O3 additive were prepared by hot press sintering method at a low sintering temperature of 870 °C compatible with LTCC (low temperature co-fired ceramics) systems, and 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. When the substitution amount further increases to 0.4 and 0.5, the α-Fe2O3 phase and La2O3 phase are found to coexist with the M-type phase, thus the multiphase structure is formed. Besides, the saturation magnetization Ms, intrinsic coercivity Hci, and Curie temperature TC of the ferrites are strongly correlated with the La–Co substitution amount. Enhanced Ms and Hci are obtained when the substitution amount varies from 0.2 to 0.4, which can exceed 3600 Gs and 4000 Oe, respectively. However, the TC decreases rapidly when the substitution amount exceeds 0.3, and a value under 410 °C is observed. It is suggested that the La3+–Co2+ ions can partially substitute the Sr2+–Fe3+ ions for the hot press sintered ferrites at low sintering temperatures, leading to improved Ms and Hci for use in microwave LTCC ferrite devices.