On the potential of hard ferrite ceramics for permanent magnet technology -- a review on sintering strategies

TL;DR

This review discusses the potential of hard ferrite ceramics, especially hexaferrites, as rare-earth-free permanent magnets, focusing on sintering strategies to improve their magnetic and mechanical properties for industrial use.

Contribution

It provides a comprehensive overview of historical and ongoing research on sintering methods for hexaferrites, highlighting challenges and solutions for industrial application.

Findings

Sintering strategies significantly influence magnetic performance of hexaferrite ceramics.

Challenges include achieving dense, mechanically robust magnets with optimal magnetic properties.

Research explores various sintering techniques to overcome manufacturing hurdles.

Abstract

A plethora of modern technologies rely on permanent magnets for their operation, including many related to the transition towards a sustainable future, such as wind turbines or electric vehicles. Despite the overwhelming superiority of magnets based on rare-earth elements in terms of the magnetic performance, the harmful environmental impact of the mining of these raw materials, their uneven distribution on Earth and various political conflicts among countries leave no option but seeking for rare-earth-free alternatives. The family of the hexagonal ferrites or hexaferrites, and in particular the barium and strontium M-type ferrites (BaFe12O19 and SrFe12O19), are strong candidates for a partial rare-earth magnets substitution, and they are indeed successfully implemented in multiple applications. The manufacturing of hexaferrites into dense pieces (i.e. magnets) meeting the requirements of the specific application (e.g. magnetic and mechanical properties, shape) is not always straightforward, which has in many cases hampered the actual substitution at the industrial level. Here, past and on-going research on hexaferrites sintering is reviewed with a historical perspective, focusing on the challenges encountered and the solutions explored, and correlating the sintering approaches with the magnetic performance of the resulting ceramic magnet.