Dependence of magnetic properties on microstructure in mechanically alloyed Nd-Fe-Ti-N

In the systems of NdxFe92-xTi8 and Nd8Fe92-yTiy, Nd-Fe-Ti intermetallic compound with ThMn12 structure has been successfully synthesized by mechanical alloying (MA) and subsequent annealing. It has been found that the ThMn12 structure exists only over a range of compositions 5≤x<11 and 616 and the TbCu7 structure for y=4 can be formed, respectively. For Nd8Fe84Ti8, MA powder annealed at 650-850 C, the phase of hexagonal TbCu7 structure is formed. With increasing the annealing temperature Ta, the metastable TbCu7 structure is transformed into the ThMn12 structure. The Curie temperature increases from 180 C for the TbCu7 structure at Ta=650 C to 300 C for the ThMn12 structure at Ta=1050 C. The nearly complete transformation from TbCu7 to ThMn12 may be achieved at Ta=960 C. All the MA prepared samples are nitrided at TN=400 C for 15 h and the nitrogenation raises the Curie temperature Tc of the phase with the ThMn12 structure to 400-450 C. Too high temperature of the nitrogenation leads to decomposition of the compounds. The dependence of the magnetic properties on the composition and heat treatment and nitriding conditions has been studied. (orig.)