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

摘要

Magnetic properties of (Nd, Pr)_(60-70)Fe_(30-20)Al_(10) 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 Nd_(60)Fe_(30)Al_(10), 3 mm for Nd_(70)Fe_(20)Al_(10), 6 mm for Pr_(60)Fe_(30)Al_(10) and 1 mm for Nd_(70)Fe_(20)Al_(10). Bulk specimens with thicknesses ranging from 100 μm to 6 mm exhibit hard magnetism with coercive force (_iH_c) ranging from 100 to 300 kA/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 100 μm for (Nd, Pr)_(70)Fe_(20)Al_(10) amorphous alloys. The critical cooling rate for the formation of amorphous phase is estimated as less than 100 K/s for (Nd, Pr)_(60-70)Fe_(30-20) Al_(10) alloys from the analyses using thermodynamic quantities.