Abstract

Recent developments in nanocrystalline and nanocomposite rare earth-transition metal magnets are reviewed and emphasis is placed on research work at IFW Dresden. Principal synthesis methods include high energy ball milling, melt spinning, mold casting and hydrogen assisted methods such as reactive milling and hydrogenation-disproportionation-desorption-recombination. These techniques are applied to NdFeB-, PrFeB- and SmCo-type systems with the aim to produce high remanence magnets with high coercivity. Concepts of maximizing the energy density in nanostructured magnets by either inducing a texture via anisotropic HDDR or hot deformation or enhancing the remanence via magnetic exchange coupling are evaluated. With respect to high temperature applications melt spun Sm(Co_0.74Fe_0.1Cu_0.12Zr_0.04)_7.5 ribbons were prepared, which showed coercivities of up to 0.53 T at 500°C. Partially amorphous Nd_60Fe_xCo_30-xAl_10(0leqxleq30) alloys were prepared by copper mold casting. The effect of transition metal content on the glass-forming ability and the magnetic properties was investigated. The Nd_60Co_30Al_10 alloy exhibits an amorphous structure shown by the corresponding diffraction pattern. A small substitution of Co by 2.5 at.% Fe results In the formation of Fe-rich crystallites embedded in the Nd-rich amorphous matrix. The Fe-rich crystallites show hard magnetic behaviour at room temperature with a coercivity value of about 0.4 T, relatively low saturation magnetization and a Curie temperature of 500 K.

• Keywords: Permanent magnets;nanocomposite materials;mechanical alloying;melt spinning;mould casting;HDDR;coercivity;Nd-Fe-B;Sm-Co;Nd-Fe-Al;