A review on structural integrity and magneto-dielectric response of rare earth substituted U-type hexagonal ferrites

There is increasing enthusiasm in research on U-type hexaferrites because they promise high ferromagnetic resonance frequencies, strong magnetoelectric coupling, high-temperature performance, and enhanced tunability via doping. This review concentrates on the structural complexities associated with U-type hexaferrites. The U-type hexaferrite structure is constructed from molecular units Z+M or 2M+Y, with space group R−3m and crystallographic parameters a and c extending from (5.73 - 5.88)Å and from (111.76 - 113.03)Å, respectively. These materials exhibit uniaxial anisotropy. The impact of rare-earth ion substitution is also discussed, as it improves magnetic anisotropy and saturation magnetization due to high magnetic moments and strong spin orbit coupling. Despite advancements in alternative synthesis routes, the sol-gel auto-combustion approach remains the most frequently used method for producing U-type hexaferrites because of its affordability and effectiveness in achieving phase purity. These materials have gained significant commercial and technological importance owing to their applications in permanent magnets, magnetic disks, and memory devices used in electrical equipment, particularly those operating at elevated frequencies.