Formation of metastable Fe–Cu alloy nanoparticles by ion implantation

The formation of the immiscible Fe–Cu nano-clusters by sequential implantations of Fe and Cu ions in crystalline Al2O3 is reported in this study. The implantation was performed at room temperature to a total dose of 2.0 × 1017 ions/cm2, changing the relative dose of Fe and Cu ions to obtain various Cu concentrations. The possibility of the metastable alloy clusters was investigated by a combined measurement of conversion electron Mössbauer spectroscopy, X-ray diffraction, magneto-resistance (MR) and magnetization. It is shown that the additional Cu implantation leads to both the transitions from super-paramagnetic to ferromagnetic states in the iron nano-clusters aggregated beforehand and also the decrease in the internal fields, suggesting the alloy formation. MR ratio has been found to decrease with increasing Cu dose, indicating also the formation of Cu nano-clusters in the matrices.