Coercivity and phase transitions of clustered Nd90-xFexAl10 bulk hard magnets

Rapidly and slowly quenched Nd90-xFexAl10 glassy alloys with thicknesses up to 3 mm were investigated comparatively by structural and magnetic measurements in the temperature range 5-800 K and external fields up to 9 T. The glass-forming ability decreases increasing Fe content. Room temperature coercivities of over 0.6T are observed, depending on composition and external field. The huge increase of the coercive field up to 5.5 T at low temperatures as well as the dependence on the cooling rate are supposed to result from the non-collinear magnetic structures developed in these amorphous alloys. From DC and AC magnetic measurements combined with neutron diffraction results we conclude that the structure, which is quenching conditions dependent, consists of a packing of nanometer-sized clusters. The topological and magnetic structures of Nd90-xFexAl10 melt-spun ribbons and cast rods in a wide range of temperatures and for different x values are modelled using the reverse Monte Carlo method (RMC). The hypotheses of a cluster model, in which exchange interactions, local random anisotropies and thermal effects are competing, are proposed.