Magnetic properties of Ce–Nd–Fe–Mo alloys and their nitrides

• We synthesize Ce1−xNdxFe12−yMoy with ThMn12 structure by melt spinning.
• An optimized nitriding profile has been identified.
• Tc values in Ce1−xNdxFe12−yMoyNz with y=1 and 1.5 exceed that of Nd2Fe14B.
• Hci in the nitrides is determined by the dominant role played by Nd.
• Substantially higher Hci and (BH)max are obtained in nitrides containing Nd.

New quaternary alloys of Ce1−xNdxFe12−yMoy with x=0, 0.2, 0.4, 0.6, 0.8, 1 and y=0, 1.5, 2 have been prepared and magnetically hardened by melt spinning. X-ray diffraction indicates that the as-spun materials exhibit the tetragonal ThMn12-type structure. Prior to nitriding, the coercivity Hci is less than 0.6 kOe in all alloys and is independent of Nd content, while the magnetization 4πM19 (measured in an applied field of 19 kOe) and Curie temperature Tc increase with added Nd content x. The effects of nitriding pressure P, time t, and temperature T on magnetic properties have been carefully evaluated on NdFe10Mo2 in order to identify the optimal nitriding parameters. The optimized nitriding profile was subsequently adopted to nitride the remaining samples. After nitrogenation, Tc and 4πM19 have been substantially enhanced primarily due to the increased Fe–Fe exchange from nitrogen induced lattice dilation. Benefitting from the positive contribution from Nd, Hci has been greatly improved in the Nd containing samples. As a result, Ce0.2Nd0.8Fe10Mo2 nitride features Hci=2.9 kOe and (BH)max=1.6 MGOe and Ce0.2Nd0.8Fe10.5Mo1.5 nitride demonstrates Hci=2.5 kOe, (BH)max=1.5 MGOe at room temperature, and Tc=337 °C, which are substantial advancements compared to the pure Ce based ThMn12-type materials previously reported.