New material for permanent magnets on a base of Nd and Fe (invited)

A new compound composed of Nd, Fe, and a small quantity of B (about 1 wt. %) has been found, which has a tetragonal structure with lattice constants a=0.880 nm and c=1.221 nm. This phase, which has the approximate composition, 12 at. % Nd, 6 at. % B and balance Fe, possesses remarkable magnetic properties. From the approach to saturation an anisotroy constant of about 3.5 MJ/m³ can be calculated, while saturation magnetization amounts to 1.35 T. The magnetization versus temperature curve shows a Curie temperature of 585 K, which is much higher than those of the Fe and light rare earth binary compounds. Based on the new compound, sintered permanent magnets have been developed which have a record high energy product. Permanent magnet properties and physical properties of a typical specimen which has the composition Nd₁₅B₈Fe₇₇ are as follows: B_r =1.23 T, H_cB =880 kA/m, H_cI =960 kA/m, (BH)_max =290 kJ/m³, temperature coefficient of B_r =−1260 ppm/K, density=7.4 Mg/m³, specific resistivity=1.4 μΩm, Vickers hardness=600, flexual strength=250 MPa.