A critical review on structural, magnetic, and electrical properties of R-type hexaferrites for microwave applications

Since their discovery, hexaferrites have emerged as technologically significant ceramic materials, attracting extensive scientific and industrial interest. Among them, R-type hexaferrites represent a distinctive class with unique crystal structures composed of repeating R blocks, which provide tunable dielectric, magnetic, and electrical characteristics. This review article discusses the structural features, synthesis strategies, and functional properties of R-type hexaferrites, with emphasis on the influence of compositional substitutions, particle size, and crystallinity on their performance. Conventional solid-state reactions and chemical routes such as sol-gel synthesis are highlighted as effective methods for tailoring their properties. Due to their excellent high-frequency response and magnetic anisotropy, R-type ferrites are promising candidates for microwave and millimeter-wave applications, including dielectric resonators, switches, and sensors. Furthermore, their potential use in longitudinal and high-density magnetic recording, wireless communication components, antennas, spintronic devices, energy storage, and biomedical technologies underscores their versatility. The article consolidates recent advancements while emphasizing the critical role of structural property correlations and synthesis control in optimizing R-type hexaferrites for next-generation electronic and communication technologies.