Size dependence of soft to hard magnetic transition in (Nd, Pr)–Fe–Al bulk amorphous alloys

Magnetic properties of (Nd, Pr)60–70Fe30–20Al10 amorphous alloys were studied for bulk specimens prepared by arc-melting. The bulk specimens with thicknesses ranging from 100 μm to 6 mm 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 6 mm for Nd60Fe30Al10, 3 mm for Nd70Fe20Al10, 6 mm for Pr60Fe30Al10 and 1 mm for Nd70Fe20Al10. Bulk specimens with thicknesses ranging from 100 μm to 6 mm exhibit hard magnetism with coercive force (iHc) ranging from 100 to 300 kA/m. The iHc of the bulk specimens tends to decrease with decreasing thickness. It is estimated that the soft to hard magnetic transition takes place approximately 100 μm for (Nd, Pr)70Fe20Al10 amorphous alloys. The critical cooling rate for the formation of amorphous phase is estimated as less than 100 K/s for (Nd, Pr)60–70Fe30–20 Al10 alloys from the analyses using thermodynamic quantities.