M-type hexaferrites: A review of the impact of rare earth substitution on magnetic properties

Abstract

The substitution of rare earths in M-type hexaferrites has attracted attention in the past decade due to their ability to modify the crystal structure and magnetic properties. However, achieving rare earth incorporation in the M-type structure is extremely challenging because they often create secondary phases during the sintering process. This study analyzes the effect of rare earth substitution on the magnetic properties of M-type hexaferrites, examining 312 samples reported in the last decade. We focus on the effects of rare earth substitution on the magnetic properties, including magnetization to saturation, remanence magnetization, coercive field, remanence squareness ratio and maximum energy product. Moreover, different fabrication routes and sintering parameters such as heating time and temperature were considered in the analysis. The results are presented in a comprehensive table showcasing the progress that rare earth-substituted hexaferrites have made in the last decade. This review provides insights into the correlations between experimental factors and synthesis parameters with purity, structural variations and the magnetic properties resulted from the rare-earths substitution. This review aims to elucidate the connections between synthesis parameters and experimental factors, with the resulting purity, structural variations, and magnetic properties of M-type hexaferrites substituted using rare-earths. In addition, a critical perspective is presented about the challenges and potential of substituted hexaferrites in the next-generation of magnetic ceramics.