Electron microscopy studies of new phases in Nd-Fe alloys

Abstract
The magnetic properties, structure, microstructure, and chemical composition of new phases found in melt-spun Nd-Fe alloys are reported. High coercivities were obtained in ribbons after a heat treatment for 10–15 min at temperatures in the range of 450–550 °C. Thermomagnetic data showed the existence of two new phases with Curie temperatures at around 250 and 340 °C, respectively. Electron microscopy observations confirmed the existence of two different iron-rich phases. One of them had 70 at. % Fe and a tetragonal structure with a=8.0 Å and c=11.9 Å, similar to Nd2Fe14B. The other one had 85 at. % Fe and a hexagonal structure with a=20.5 Å and c=11.5 Å. These phases are probably ternary Nd-Fe-O stabilized by oxygen. The hexagonal phase is believed to correspond to the phase with a Curie temperature of 250 °C.

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