Immiscible alloys have been rapidly solidified for the preparation of granular materials with giant magnetoresistance properties. Au-based (Au–Co and Au–Fe) and Cu-based (Cu–Co and Cu–Fe) systems have been investigated. Single supersaturated solid solution has been obtained for Au–Fe, whereas three FCC solid solutions with different Co content have been found for Au–Co. For Cu–Co and Cu–Fe a limit of solubility in Cu has been observed. Ni additions to Cu–Fe strongly enhance solid solubility. A thermodynamic analysis has been used to describe the competition between partition-less solidification and phase separation in undercooled liquid.