High-field magnetization and coercivity of hard magnetic mold-cast Nd80Fe20

Nd80Fe20 bulk specimens were prepared by copper mold casting and their structure and magnetic properties were studied. The specimens contain 73wt% elemental Nd and 27wt% hard magnetic Fe–Nd regions, which are a mixture of amorphous and nanocrystalline phases. The average composition of the Fe–Nd regions is Nd45Fe55. The presence of elemental Nd leads to multiple magnetic transitions below 30K whereas the Fe–Nd regions have a Curie temperature of 529K. Above 30K, the specimens show a single-phase hard magnetic behavior superimposed on the large susceptibility due to paramagnetic Nd and a noncollinear magnetic structure of Fe moments. At T⩽30K, two-phase demagnetization curves were observed due to the additional ferromagnetic contribution of metastable fcc Nd. The coercivity of the hard magnetic Fe–Nd regions is strongly temperature dependent, decreasing from 6.4T at 4.2K to almost zero at temperatures close to the Curie temperature. The shape of the initial magnetization curve and the remanence values of a...