Effect of Co addition on the microstructure and magnetic properties of Nd9.5Febal.Co x Nb2.5Zr0.5B15 (x =0, 10, 20) bulk magnets

Abstract: Cylindrical Nd9.5Febal.Co x Nb2.5Zr0.5B15 (x =0, 10, 20) magnets with diameter of 0.9–1.5mm have been prepared by directly casting method. TMA and DSC analysis show that doping Co may enhance the glass forming ability and refine the grain size of the directly cast magnets effectively. Nevertheless, the amorphous phase is easily to appear at the peripheral region but not at the interior region, leading to much inhomogeneous microstructure especially when too high Co content (x =20) is added. Magnetic measurements show that higher maximum energy product and coercivity can only be obtained in Co-free magnets with smaller diameter (⩽0.9mm), while higher maximum energy product and coercivity could be appeared in Co-doped magnets (x =10) with larger diameter (1.1–1.3mm in diameter). [Copyright &y& Elsevier]