The influences of additives in M−type (Ba and Sr) hexaferrites’ microstructure, sintering and magnetic properties: A review

Abstract

Interest in the utilization of M−type hexaferrites in magnetic applications as a substitution for rare earth minerals is rapidly growing due to the low cost and compatible magnetic properties of such materials. However, low magnetic properties and high sintering temperatures are the primary drawbacks that limit the use of SrM and BaM in various applications. Therefore, it is essential to carry out processes aimed at reducing the sintering temperature and enhancing magnetic properties beyond the threshold of 0.125 kOe coercivity, 0.5 mr/ms, and achieving higher remanence values to make them suitable for hard magnetic applications. These improvements can be achieved through synthesis techniques involving substitution and/or additives. Notably, numerous studies have been conducted on different synthesis methods and substitution techniques, and they have reached their limits. Therefore, there is a current need for comprehensive reviews and studies on the effects of additives and sintering aids. In this paper, we review investigations and studies that focus on the impact of additives, namely silica, CaO, CaCO3, Bi2O3, B2O3, CuO, and Al2O3, on the microstructure, sintering temperature, and magnetic properties of SrM and BaM hexaferrites.