Size dependence of soft to hard magnetic transition in (Nd, Pr)-fe-al bulk amorphous alloys

Magnetic properties of (Nd, Pr)_60-70Fe_30-20Al₁₀ amorphous alloys were studied for bulk specimens prepared by arc-melting. The bulk specimens with thicknesses ranging from 100μm to 6mm were prepared as fragments, which were obtained by crashing a mother alloy followed by arc melting. The bulk specimens exhibit an amorphous state up to 6mm for Nd₆₀Fe₃₀Al₁₀, 3mm for Nd₇₀Fe₂₀Al₁₀, 6mm for Pr₆₀Fe₃₀Al₁₀ and 1mm for Nd₇₀Fe₂₀Al₁₀. Bulk specimens with thicknesses ranging from 100μm to 6mm exhibit hard magnetism with coercive force (_iH_c) ranging from 100 to 300kA/m. The _iH_c of the bulk specimens tends to decrease with decreasing thickness. It is estimated that the soft to hard magnetic transition takes place approximately 100μm for (Nd, Pr)₇₀Fe₂₀Al₁₀ amorphous alloys. The critical cooling rate for the formation of amorphous phase is estimated as less than 100K/s for (Nd, Pr)_60-70Fe_30-20 Al₁₀ alloys from the analyses using thermodynamic quantities.