Magnetic performance of SrFe₁₂O₁₉–Zn_0.2Fe_2.8O₄ hybrid magnets prepared by spark plasma sintering

Abstract

In the last few years, significant effort has again been devoted to ferrite-based permanent magnet research due to the so-called rare-earth crisis. In particular, a quest to enhance ferrites maximum energy product, BH max, is underway. Here, the influence of composition and sintering conditions on the microstructure and consequently magnetic properties of strontium ferrite-based hybrid composites was investigated. The powder mixtures consisted of hydrothermally synthesised Sr-ferrite with hexagonally shaped platelets with a diameter of 1 μm and thickness up to 90 nm, and a soft magnetic phase in various ratios. Powders were sintered using a spark plasma sintering furnace. The crystal structure, composition and microstructure of the starting powders and hybrid magnets were examined. Their magnetic properties were evaluated by vibrating sample magnetometer, permeameter and by single-point-detection measurements.

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“…Guzmán-Mínguez et al improved the magnetic performance of strontium ferrite sintered magnets using silica by tuning sintering parameters [81]. Exchange coupling between the hard and soft magnetic phases is one of the magnetic interactions that could lead to an increase in (BH)max [82,83]. The latter tends to increase with an increase in the coercivity, HcJ (the contribution of the hard phase), and/or the saturation magnetization, MS (the contribution of the soft phase) [84,85].…”

“…Second, the particle size of the soft phase is limited by the selected hard phase. So, to effectively exchange the hard and soft magnetic phases, the particle size of the soft phase should not exceed twice that of the domain-wall width of the hard-phase material [83,88]. Some recent studies even indicated that for an efficient exchange coupling, the phases also need to have some degree of structural matching [96,97].…”

“…Nevertheless, a (BH)max of 14.3 kJ/m 3 for a hard-soft magnetic ceramic composite was reported by Debangsu Roy and P. S. Anil Kumar [102], in which they presented a hard-soft magnetic composite consisting of BaCa2Fe16O27 as the hard phase and Fe3O4 as the soft phase. Torkian and Ghasemi [103] presented Exchange coupling between the hard and soft magnetic phases is one of the magnetic interactions that could lead to an increase in (BH) max [82,83]. The latter tends to increase with an increase in the coercivity, H cJ (the contribution of the hard phase), and/or the saturation magnetization, M S (the contribution of the soft phase) [84,85].…”

“…The latter tends to increase with an increase in the coercivity, H cJ (the contribution of the hard phase), and/or the saturation magnetization, M S (the contribution of the soft phase) [84,85]. Therefore, by choosing wisely the constituent phases of the hybrid magnet, the energy product can be increased beyond the energy product of the hard phase alone [83]. Although this seems like an elegant solution, several requirements and restrictions have to be considered for an effective exchange.…”