Appearance of ferromagnetism in f.c.c. solid solutions of binary and ternary Fe–Cu-based systems prepared by mechanical alloying technique

The ferromagnetic f.c.c. solid solutions are formed by mechanical alloying in the Fe–Cu binary systems containing less than 60% of iron. The Curie temperature of the alloy decreases with decreasing iron concentration. The expansion of average atomic volume of the alloys is about 1.6% of pure copper and 5.3% of f.c.c. γ-iron regardless of copper content except for dilute iron alloys. It is suggested from the present work that the ferromagnetism in the Fe–Cu alloys originates when the atomic volume is expanded by a certain value (5.3% of γ-iron is enough), and when a certain number of neighboring iron atoms exist to percolate the ferromagnetic interaction and possibly to generate the magnetic moment of iron. In the studies of ternary systems silver atoms hardly dissolved in Fe–Cu solution, whereas gold atoms formed solid solution.