Co–Al-substituted strontium hexaferrite for rare earth free permanent magnet and microwave absorber application

Permanent magnets (PMs) have tremendous demand because of their applicability in various electronic devices. Rare earth (RE) elements are the major component in fabricating these PMs. Tremendous research interest has been generated over the last decade to design the RE-free PMs because of the ever-increasing cost of REs and shortage of their supply. Hexagonal ferrites show incredible potential as RE-free magnets owing to their high coercivity and moderate saturation magnetization. In this work, we focused on improving the magnetic properties of Sr0.8Ca0.2AlxCoxFe12−2xO19 hexagonal ferrites with respect to Co2+–Al3+ co-substitution synthesized by the sonochemical method. Improved saturation magnetization of 64.4 emu g−1, coercivity of 13.2 kOe, and a remnant ratio of 0.71 was achieved upon Co2+–Al3+ substitution. The prepared materials were also tested for microwave absorption characteristics, where a maximum reflection loss of −35.4 dB at 12.36 GHz was obtained. Results were discussed in light of the synthesis method, Co2+–Al3+ substitution, and electrical properties. Such improvement in the electromagnetic properties make these ferrites suitable for use as RE-free PMs and microwave absorbers.