Publication: Dense strontium hexaferrite-based permanent magnet composites assisted by cold sintering process
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Elsevier Science SA
The use of rare-earth-based permanent magnets is one of the critical points for the development of the current technology. On the one hand, industry of the rare-earths is highly polluting due to the negative environmental impact of their extraction and, on the other hand, the sector is potentially dependent on China. Therefore, investigation is required both in the development of rare-earth-free permanent magnets and in sintering processes that enable their greener fabrication with attractive magnetic properties at a more competitive price. This work presents the use of a cold sintering process (CSP) followed by a post annealing at 1100 degrees C as a new way to sinter composite permanent magnets based on strontium ferrite (SFO). Composites that incorporate a percentage <= 10% of an additional magnetic phase have been prepared and the morphological, structural and magnetic properties have been evaluated after each stage of the process. CSP induces a phase transformation of SFO in the composites, which is partially recovered by the post thermal treatment improving the relative density to 92% and the magnetic response of the final magnets with a coercivity of up to 3.0 kOe. Control of the magnetic properties is possible through the composition and the grain size in the sintered magnets. These attractive results show the potential of the sintering approach as an alternative to develop modern rare-earth-free composite permanent magnets.
©2022 The Author(s). Published by Elsevier B.V. CC_BY_NC_ND_4.0 This work has been supported by the Ministerio Español de Ciencia e Innovación (MICINN), Spain, through the projects MAT2017-86540-C4-1-R and RTI2018-095303-A-C52, and by the European Commission through Project H2020 No. 720853 (Amphibian). C.G.-M. and A.Q. acknowledge financial support from MICINN through the “Juan de la Cierva” program (FJC2018-035532-I) and the “Ramón y Cajal” contract (RYC-2017-23320). S. R.-G. gratefully acknowledges the financial support of the Alexander von Humboldt foundation, Germany. A.S. acknowledges the financial support from the Comunidad de Madrid, Spain, for an “Atracción de Talento Investigador” contract (No. 2017-t2/IND5395).