High-coercivity Nd_90-xFe_xAl₁₀ bulk amorphous alloys

Extensive magnetic studies on Nd_90-xFe_xAl₁₀ (x = 35 ∼ 50) amorphous alloys in the shape of both melt-spun ribbons with thicknesses between 25 and 150 μm and rods with diameters no larger than 3 mm prepared by mould casting and suction casting indicate a complex magnetic behaviour depending on the Fe content. The microstructure and magnetic properties are strongly dependent on the cooling rate and the preparation technique. The high values of the coercive field of Nd_90-xFe_xAl₁₀ amorphous samples in the as-cast state as well as their increase by the decrease of the cooling rate and temperature result from the formation of very small metastable or non-equilibrium clusters, whose size vary as a function of the quench rate. The presence of these magnetic clusters is evidenced by multiphase magnetic transitions observed from the ac-susceptibility measurements at low temperatures.