Ca–Al double-substituted strontium hexaferrites exhibit record-high coercivities up to 21.3 kOe.

The review is devoted to compounds and materials demonstrating extremely high magnetic hardness. The recent advances in the synthesis of modern materials for permanent magnets are considered, and a range of exotic compounds interesting for fundamental research is described. The key details of chemical composition, crystal structure and magnetic microstructure responsible for the appearance of high magnetic anisotropy and giant coercivity are analyzed. The challenges of developing the title materials are noted and strategies for their solution are discussed.The bibliography includes 389 references.

A fast method for the synthesis of ε-Fe₂O₃, yielding 100% pure material with a variable FMR frequency, is proposed.

Herein, we demonstrate for the first time compact ferrite ceramics with giant coercivity. The materials are manufactured via sintering single-domain Sr_0.67Ca_0.33Fe₈Al₄O₁₉ particles synthesized by a citrate-nitrate auto-combustion method. The obtained ceramics show coercivities up to 22.5 kOe and natural ferromagnetic resonance frequencies (NFMR) in a sub-THz range of 160–282 GHz. At a maximum density of 95%, the sample displays coercivity of 18.5 kOe, which is the highest value among dense ferrite materials reported so far. In addition, we report an unusual blueshift of the NFMR frequency from 160 to 200 GHz, which occurs during material sintering.

${\mathrm{Fe}}^{3+} S=5/2$ ions form saw-tooth-like chains along the $a$ axis of the oxoselenite ${\mathrm{Fe}}_2\mathrm{O}{\left({\mathrm{SeO}}_3\right)}_2$ and an onset of long-range magnetic order is observed for temperatures below $T_C=105$ K. This order leads to distinct fingerprints in phonon mode linewidths and energies as resolved by Raman scattering. In addition, new excitations with small linewidths emerge below $T=150$ K, and are assigned to two-magnon scattering processes with the participation of flat-band and high energy magnon branches. From this a set of exchange coupling constants is estimated. The specific ratio of the saw-tooth spine-spine and spine-vertex interactions may explain the instability of the dimer quantum ground state against an incommensurate 3D magnetic order.