While the regular/anomalous eutecti

While the regular/anomalous eutectic banding is frequent in the present samples, eutectic/primary phase bands were found at places as in the right part of Fig. 1. Fig. S2 (Supplementary Information) shows their occurrence in the arc melted ingot. The transition from a eutectic to a single phase has been frequently reported [8,10] and modelled [11] in off-eutectic alloys. Since the leading primary phase is Co2Si, the local composition must have been shifted to the other side of the eutectic. This is understood by considering the formation of the large CoSi crystals at the beginning of solidification which must have consumed Co enriching the melt in Si along the liquidus line. Although it can be envisaged that the growth rates in the transition zone were of the order derived above, the verification with the current model [11] cannot be performed because of the uncertainty of the starting off-eutectic composition.