Embedded iron nano-clusters prepared by Fe ion implantation into MgO crystals

Iron precipitation and the accompanying magnetization and magnetoresistance (MR) were investigated in MgO(1 0 0) crystals implanted with Fe ions of 100 keV energy. MR properties were measured at room temperature. A giant magnetoresistance effect was observed at a dose of 2.0×1017 ions/cm2 and the obtained MR ratio was approximately 3.5% for the fields of 12 kOe for the samples post-annealed at 300 °C in Ar. Conversion electron Mِssbauer spectroscopy (CEMS) was used to identify physical states of the implanted irons. CEMS shows that the transition from superparamagnetism to ferromagnetism in the precipitated iron nano-clusters critically depends on the implantation dose and post-annealing and that with increasing dose over 2.0×1017 ions/cm2 a ferromagnetic component appears in the Fe implanted MgO samples.