Crystallization of amorphous Co78-xMnxB10Si12 alloys

Abstract

Amorphous Co78-xMnxB10Si12 (x = 10, 15, 20, 25) alloys were fabricated using the meltspinning process in order to study the effect of Mn addition on the crystallization of the Co-rich amorphous alloy. In general, thermal stability of the amorphous structure was greatly improved by the presence of Mn, delaying the onset of crystallization by 100 degrees C as the Mn content was increased from 10 to 25 at. pct. Due to the delay of crystallization, Co53Mn25B10Si12, unlike other compositions, exhibited a uniform grain size distribution, relatively free of any structural defects in the fully devitrified state. It was also found that Co2MnSi was the first crystalline phase to nucleate in the amorphous matrix and became the increasingly dominant phase in the fully devitrified structure as Mn content was increased. Saturation magnetization of the as-cast alloys decreased with increasing Mn content and eventually became paramagnetic at 20 at. pct. During devitrification, all of the studied alloys became ferromagnetic from nucleation of Co2MnSi and Co. The magnetic transition temperatures correlated well to the observed changes in the microstructure.