La-Co co-substituted M-type ferrite, which was first reported at the end of the 20th century, as the cornerstone of high-performance permanent magnet ferrites, has received increasing attention from researchers around the world. 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 order to meet the increasing performance requirements of ferrite materials, it is imperative to clarify the mechanism behind the enhancement of magnetic anisotropy, and at the same time seek the guiding principles that are helpful to develop high-performance product quickly and economically. But its mechanism at a microscopic level has not been explained. This review comprehensively analyzes various studies aiming at pinpointing the crystal sites of Co substitution within the lattice. These investigations including neutron diffraction, nuclear magnetic resonance, and Mössbauer spectroscopy can reveal the fundamental origins behind the enhancement of magnetic anisotropy, thereby providing valuable insights for material design strategies aiming at further enhancing the magnetic properties of permanent magnet ferrites.

The exploration of co-substitution sites has yielded noteworthy findings. Through careful examination and analysis, researchers have discovered the complex interplay between Co ions and the lattice structure, revealing the mechanisms of enhanced magnetic anisotropy. The current mainstream view is that Co ions tend to occupy more than one site, namely the 4f₁, 12k, and 2a sites, all of which are located within the spinel lattice. However, there have also been differing viewpoints, implying that further exploration is needed to uncover the primary controlling factors influencing Co occupancy. It is worth noting that the identification of specific Co substitution sites, especially the spin-down tetrahedron 4f₁, has achieved targeted modifications, ultimately fine-tuning the magnetic properties with remarkable precision.

Furthermore, the reviewed research emphasizes the pivotal role of crystallographic engineering in tailoring the magnetic characteristics of ferrite materials. By strategically manipulating Co substitution, researchers have utilized 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. With a detailed understanding of Co-substitution mechanisms, researchers are preparing to open up new avenues for developing next-generation ferrite materials with enhanced magnetic properties.