Structure and magnetic properties of mechanical alloyed Nd–Fe–Ti compounds and their nitrides

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Abstract
The Nd–Fe–Ti intermetallic compounds with a ThMn12 structure have been successfully prepared by mechanical alloying and then annealed. It has been found that the phase of the hexagonal TbCu7 structure is formed in Nd8Fe84Ti8 mechanical alloy powders annealed at temperatures ranging from 650 to 850 °C. With an increase in the annealing temperature Ta, the metastable TbCu7 structure transforms into a ThMn12 structure at Ta=900 °C. Consequently, the Curie temperature increases from 180 °C of TbCu7 structure at Ta=650 to 300 °C of ThMn12 structure at Ta=1050 °C. In the series of NdxFe92−xTi8 annealed at 960 °C for 30 min, it has been observed that the ThMn12 structure exists only over the range of compositions of 5≤x2Zn17 is formed for x≥11. All the compounds are nitrited at 400 °C for 15 h, and the Curie temperatures are raised from 400 to 450 °C. The Nd9Fe83Ti8 powder, annealed at 960 °C for 30 min, and nitrided at 400 °C for 15 h, has a coercivity iHc=2.3 kOe. The low coercivity perhaps mainly results from an excessive growth of α‐Fe grains due to the high annealing temperature necessary for forming the hard magnetic phase Nd(Fe,Ti)12Nδ.

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