Progress of magnetic anisotropy enhancement mechanism in high-performance La-Co co-substituted M-type ferrites

La-Co co-substituted M-type ferrite,first reported at the end of the 20th century,has garnered continuous attention from researchers worldwide,serving as the cornerstone for high-performance permanent magnet ferrites.The unquenched orbital moments of Co²⁺ play a pivotal role in enhancing the uniaxial anisotropy of M-type ferrites.However,a comprehensive understanding of its microscopic mechanism remains elusive.In response to the escalating performance demands of ferrite materials,elucidating the mechanism behind magnetic anisotropy enhancement becomes imperative,alongside the quest for guiding principles facilitating the swift and cost-effective development of high-performance products.but its mechanism at the microscopic level has not been explained.This review encompasses a comprehensive analysis of various studies aimed at pinpointing the crystal sites of Co substitution within the lattice.These investigations including neutron diffraction,nuclear magnetic resonance,and Mössbauer spectroscopy delve into the fundamental origins underlying the enhancement of magnetic anisotropy,thereby furnishing valuable insights for material design strategies geared towards further augmenting the magnetic properties of permanent magnet ferrites.The exploration of Co-substitution sites has yielded noteworthy findings.Through meticulous examination and analysis,researchers have discerned the intricate interplay between Co ions and the lattice structure,shedding light on the mechanisms governing magnetic anisotropy enhancement.The current mainstream view is that Co ions tend to occupy more than one site,namely the 4<i>f</i>₁,12<i>k</i>,and 2<i>a</i> sites,all of which are located within the spinel lattice.However,there have also been differing viewpoints,indicating that further exploration is needed to uncover the primary controlling factors influencing Co occupancy.Notably,the identification of specific Co substitution sites,especially the spin-down tetrahedron 4<i>f</i>₁,has enabled targeted modifications,culminating in the fine-tuning of magnetic properties with remarkable precision.Furthermore,the reviewed studies underscore the pivotal role of crystallographic engineering in tailoring the magnetic characteristics of ferrite materials.By strategically manipulating Co substitution,researchers have harnessed the intrinsic properties of the lattice to amplify magnetic anisotropy,thereby unlocking new avenues for the advancement of permanent magnet ferrites.In conclusion,the collective findings outlined in this review herald a promising trajectory for the field of permanent magnet ferrites.Armed with a nuanced understanding of Co-substitution mechanisms,researchers are poised to chart novel pathways toward the development of next-generation ferrite materials boasting enhanced magnetic properties.