A shock compaction technique has been successfully applied for the consolidation of hard magnetic powders without appreciable changes in the phase structure and grain size. Pr–Fe–B and Sm–Fe–N materials, prepared with the application of melt spinning and mechanical alloying, respectively, were shock compacted with a shock wave speed of 1200 m/s and a pressure of 4.4 GPa. We found that the coercivity of high RE containing material, for which the magnetic hardness is controlled by good magnetic separation of magnetic grains by a RE-rich paramagnetic phase, decreases slightly, by $\sim$ 5 %, due to the closer proximity of the crystallites in a dense material. For low RE, exchange coupled materials, the densification does not change the coercivity.

Charge-transfer insulators are the parent phase of a large group of today's unconventional high-temperature superconductors. Here we study experimentally and theoretically the interband excitations of the charge-transfer insulator silver fluoride ${\mathrm{AgF}}_2$, which has been proposed as an excellent analog of oxocuprates. Optical conductivity and resonant inelastic x-ray scattering on ${\mathrm{AgF}}_2$ polycrystalline sample show a close similarity with that measured on undoped ${\mathrm{La}}_2{\mathrm{CuO}}_4$. While the former shows a charge-transfer gap $\sim 3.4$ eV, larger than in the cuprate, $dd$ excitations are nearly at the same energy in the two materials. Density functional theory and exact diagonalization cluster computations of the multiplet spectra show that ${\mathrm{AgF}}_2$ is more covalent than the cuprate, in spite of the larger fundamental gap. Furthermore, we show that ${\mathrm{AgF}}_2$ is at the verge of a charge-transfer instability. The overall resemblance of our data on ${\mathrm{AgF}}_2$ to those published previously on ${\mathrm{La}}_2{\mathrm{CuO}}_4$ suggests that the underlying charge-transfer insulator physics is the same, while ${\mathrm{AgF}}_2$ could also benefit from a proximity to a charge density wave phase as in ${\mathrm{BaBiO}}_3$. Therefore, our work provides a compelling support to the future use of fluoroargentates for materials' engineering of novel high-temperature superconductors.