Progress and perspectives on transition- and rare-earth-doped spinel ferrites for environmental and microwave high-frequency applications: A review

Spinel ferrites are versatile materials with tunable magnetic, electrical, and structural properties, making them suitable for a wide range of modern technologies. These compounds, represented as MFe 2 O 4 (M = Ni2+, Co2+, Zn2+, Mn2+), possess a cubic spinel structure, in which the cation distribution between tetrahedral (A) and octahedral (B) sites determines their functional behavior. Various synthesis routes, including sol-gel, co-precipitation, hydrothermal, and solid-state methods, are used to control their morphology and particle size. Characterization through XRD , FTIR , SEM, and VSM reveals their structural and magnetic features. This review summarizes recent progress in the synthesis and characterization of spinel ferrites and their applications in microwave absorption, sensors, catalysis, data storage, and biomedical devices, along with insights into future research directions. Rare-earth and transition metal dopants occupy different lattice sites in spinel ferrites. The role of cation substitution in tailoring the properties of spinel ferrites, with particular focus on the distinction between transition metal and rare-earth dopants (e.g., La 3+ , Nd 3+ , Sm 3+ ). Rare-earth ions, owing to their larger ionic radii and strong spin–orbit coupling, predominantly occupy the B (octahedral) sites, thereby influencing cation distribution between A (tetrahedral) and B sites. This redistribution significantly alters superexchange interactions, leading to notable changes in magnetic behavior, dielectric response, and microwave absorption properties. Consequently, controlled doping provides an effective strategy to optimize spinel ferrites for advanced technological applications.