$\mathrm{Th}{\mathrm{Mn}}_{12}$ nitrides are good candidates for high performance permanent magnets. However, one of the remaining challenges is to transfer the good properties of the powder into a useful bulk magnet. Thus, understanding the denitrogenation process of this phase is of key importance. In this study, we investigate the magnetic and structural stability of the ${({\mathrm{Nd}}_{0.75},{\mathrm{Pr}}_{0.25})}_{1.2}{\mathrm{Fe}}_{10.5}{\mathrm{Mo}}_{1.5}{\mathrm{N}}_x$ compound ($x=0$ and 0.85) as function of temperature by means of neutron powder diffraction. Thermal dependence of the lattice parameters, formation of $\alpha$-(Fe,Mo), as well as the nitrogen content in the nitrides are investigated by heating the compounds up to 1010 K. The decomposition takes place mainly via the formation of the $\alpha$-(Fe,Mo) phase, which starts at around 900 K, whereas the nitrogen remains stable in the lattice. Additionally, we show that the magnetic properties of the nitrides [$M\left(4\text{T}\right)=90$ ${\mathrm{Am}}^2$/kg and $H_c=0.55$ T] are maintained after the thermal treatments up to 900 K. This study demonstrates that the $\mathrm{Th}{\mathrm{Mn}}_{12}$ nitrides with the Mo stabilizing element offer good prospects for a bulk magnet provided an adequate processing route is found.

• Received 27 September 2020
• Revised 17 December 2020
• Accepted 12 January 2021

DOI:https://doi.org/10.1103/PhysRevMaterials.5.014415