Magnetic and structural properties of nanocomposite permanent magnet produced from crystallization of Pr4Fe67Nb4Cu2Zr1B22 alloy

Present research work narrates synthesis, structural, thermal and magnetic characteristics of Pr4Fe67Nb4-Cu2Zr1B22 nanocomposite magnets. Amorphous Pr4Fe67Nb4Cu2Zr1B22 rods were produced through injection casting technique and permanent magnetic characteristics were obtained by one-step annealing the amorphous rods. XRD analysis elucidated that as-cast rods have amorphous phase structure and annealed magnets have tetragonal Pr2Fe14B hard phase, cubic structural alpha-Fe phase and tetragonal Fe3B soft phase. Optimal annealed magnet composed of 63% Pr2Fe14B hard phase, 26% alpha-Fe and 11% Fe3B soft phases with mean grain sizes around 51.6 +/- 1 nm for Pr2Fe14B, 25.4 +/- 2 nm for alpha-Fe and 21.5 +/- 2 nm for Fe3B phases. Microscopic and atomic probe studies showed that the annealed magnet consists of Pr2Fe14B, alpha-Fe, Fe3B nanosized grains interlinked with thin grain boundaries. Henkel curve evidenced the existence of inter-grain exchange coupling between magnetic nanophase grains. Magnetic hysteresis measurements revealed that Pr4Fe67Nb4Cu2Zr1B22 nanocomposite magnet yielded maximum magnetic characteristics such as coercivity Hc of 382 kA/m, remanence Br of 0.70 T and maximum energy product (BH)max of 64.2 kJ/m3 with rare earth to iron ratio 4:67.