Study of microstructure and correlative magnetic property in bulk Fe61Nd10B25Nb4 permanent magnet

The correlation between microstructure and magnetic property of a bulk Fe61Nd10B25Nb4 alloy are investigated. The microstructure of the as-cast Fe61Nd10B25Nb4 alloy shows a small amount of NbFeB phase with a grain size of 500 nm embedded in an amorphous matrix. The as-cast sample shows soft magnetic behavior at room temperature, after a heat treatment the hard magnetic properties are observed. A fully dense bulk Fe61Nd10B25Nb4 permanent magnet is obtained with an intrinsic coercivity (iHc) of 1191 kA/m and a maximum energy product ((BH)max) of 31.7 kJ/m3 after annealing at 943 K for 20 min. The corresponding microstructure consists of Nd2Fe14B, NdFe4B4 and NbFeB phases. The existence of the hard magnetic Nd2Fe14B phase is the reason resulting in a high value of iHc. On the other hand, the influences of NdFe4B4 and NbFeB phases in the annealed specimen on the magnetic properties are also discussed.