Synthesis and Properties of Ferromagnetic Bulk Amorphous Alloys

Since an amorphous phase in Au-Si system was synthesized for the first time by rapid solidification in 1960[1], a large number of amorphous alloys have been prepared by various rapid solidification techniques. As the main amorphous alloy systems, one can list up the noble metal-, Fe-, Co-, Ni-, Ti-, Zr-, Nb-, Mo-, lanthanide(Ln)-, Al- and Mg-based alloys. Among these alloy systems, Fe-[2], Co-[2] and Al-[3]based amorphous alloys have been used in application fields of magnetic and high specific-strength materials. Thus, Fe- and Co-based amorphous alloys have gained the most important position as engineering amorphous alloys. When special attention is paid to Fe-based amorphous alloys, Fe-P-C alloys were synthesized in 1967[4] as the first Febased amorphous alloy. Subsequently, engineering important (Fe,Co)-Si-B amorphous alloys have been developed in 1974[5][6], followed by the formation of (Fe,Co,Ni)-(Cr,Mo,W)-C in 1978[7], (Fe,Co,Ni)-(Zr,Hf) in 1980[8] and then (Fe,Co,Ni)-(Zr,HfNb)-B amorphous alloys in 1981[9]. The (Fe,Co)-Si-B amorphous alloys have been used in many application fields as soft magnetic materials[2]. However, after 1981, nobody have succeeded in finding a new amorphous alloy in Fe- and Co-based systems by rapid solidification from liquid phase. Besides, all these amorphous alloys have serious disadvantages that high cooling rates above 105 K/s are required for glass formation and the resulting sample thickness is limited to less than about 50 μm[ 10]. Great efforts have been devoted to find Fe- and Co-based amorphous alloys with a high thermal stability of supercooled liquid against crystallization and a high glass-forming ability (GFA). Very recently, we have succeeded in finding new ferromagnetic bulk amorphous alloys with critical sample thicknesses ranging from I to 15 mm in Fe-(AI,Ga)-(P,C,B,Si)[11]-[14], (Fe,Co,Ni)-(Zr,IHf,Nb)- B[15]-[17], (Fe,Co)-(Zr,Hf)-(Nb,Ta)-(Mo,W)-B[18], (Fe,Co)-Ln-B[19] (Ln=lanthanide metal) and (Nd,Pr)-Fe-Al[20]-[22] systems. In this review, we present the formation, thermal stability, mechanical strength and magnetic properties of these new ferromagnetic bulk amorphous alloys.