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Abstract: M-type hexaferrite magnets constitute together the rare-earth magnets the most employed magnets in the world. Even if ferrite magnets have smaller energy product and lower magnetization saturation than rare-earth permanent magnets (PMs), currently ferrite magnets represent the most widely used PMs, covering 80% of the PM market production [1,2]. Recently, a strong effort is being performed to improve the magnetic properties of ferrites with the scope of substituting partially rare-earth magnets. Most of the strategies involve the nanostructuration of the ferrites and/or the development of hybrid compounds [3]. A bottleneck for the production of these magnets is that standard sintering process requires high temperatures and oxidizing atmosphere that produces the destruction of the nanostructure and several chemical changes. Different novel strategies as out-of-equilibrium or cold sintering processes are mainly considered[2,4]. In our presentation we will show the production of dense ferrite-based magnets by high pressure multi-Anvil press at low temperatures. This press applies quasi-isotropic pressures in the range up to 20 GPa and temperatures up to 1200°C. We demonstrate that the consolidation of micrometric hexaferrite (SrFe12O19) powders is possible at temperatures below 1000°C, below the standard sintering temperatures. In addition, dense hybrid magnets were obtained composed of micrometric hexaferrites and soft high magnetization metal Fe or FeCo NPs applying pressures up to 6 GPa and low temperatures (250°C). A deep study, including structural, morphological and magnetic characterizations, has been performed to determine the influence of the temperature and pressure consolidation conditions in the properties of these novel magnets. Magnetic characterizations show that hybrid magnets exhibit larger magnetization than ferrites and single step hysteresis loops. Single Point Detection characterizations indicate that the anisotropy field of the hybrid magnets is similar to that of the ferrite magnets. These results suggest that the two moieties componing the high pressure consolidated magnets have similar properties than the original micro and nano powders, but they are magnetic coupled during the reversal process. High pressure consolidation appears as a promising technique to obtain nano-based metal-oxide hybrid magnets with promising hard properties.
Keywords: ferrite magnets, high pressure consolidation, low temperatures
Published in RUNG: 19.10.2023; Views: 3106; Downloads: 9
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