Synthesis of iron based alloy nanoparticles by ion implantation and the magnetic properties.

通过在绝缘氧化物中注入高剂量磁性离子合成的金属-绝缘体纳米复合层提供了巨大的磁性隧道结等有吸引力的结构。在α-Al_2O_3单晶中注入100 keV的Fe^+离子，发现了明显的隧道磁阻效应，注入层的磁阻比约为7 ~ 8%。所得的数值大约是用射频溅射法制备的类似颗粒Fe/Al_2O_3薄膜的两倍。此外，我们还成功地在Al_2O_3基体中通过顺序注入Fe和Co离子合成了纳米级的FeCo合金簇。在FeCo颗粒层中，合金化导致铁磁矩增大。从结果来看，预计室温下的MR比将增加到10%以上。通过这些研究，我们用转换电子穆斯堡尔能谱（CEMS）获得了注入铁离子聚集态的详细信息。CEMS在原子尺度上为这种表征提供了高度敏感和微观的手段，特别是当它与大量选择的^<57>Fe注入相结合时。在这些研究中，我们报道了通过改变注入能量为100 keV的Al_2O_3基质中的^<57>Fe和^<59>Co离子的相对数量，TMR效应显著增强，并且在Fe-， Co-和FeCo颗粒膜中呈现出室温下最大的MR比。此外，在室温下进行了^<57>Fe和^<63>Cu离子的注入，总剂量为1.5×10^<17>离子/cm^2，射体能量为74-105 keV。CEMS和掠角x射线衍射（GXRD）结果表明，在SiO_2衬底中注入Fe导致Si原子溶解在析出的铁纳米团簇中。此外，Fe/Al_2O_3和Fe/SiO_2颗粒中Cu离子的加入促进了超顺磁性向铁磁性的转变，表明形成了亚稳的Fe-Cu合金纳米团簇。少

Metal-insulator nanocomposite layers synthesized by high dose implantation of magnetic ions into insulating oxides provide attractive structures such as giant magnetic tunneling junctions. An eminent tunneling magnetoresistance (TMR) effect was observed in α-Al_2O_3 single crystals implanted with 100 keV Fe^+ ions, where the implanted layers exhibit a magnetoresitance (MR) ratio of about 7〜8%. The obtained value is about twice as large as that observed for similar granular Fe/Al_2O_3 films prepared by rf sputtering. Furthermore, we have succeeded in synthesizing nanosizedclusters of FeCo alloys in the Al_2O_3 matrices by sequential implantation of Fe and Co ions. It was also demonstrated in the FeCo granular layers that the alloying leads to an increase of the iron magnetic moment. From the result it is expected for the MR ratio to increase to a value of more than 10% at room temperature.Through these studies we have obtained detailed information on the aggregation states of implanted … More Fe ions by means of conversion electron Mossbauer spectroscopy (CEMS). CEMS provides highly sensitive and microscopic means in atomic scale for such characterization especially when it is combined with the mass-selected ^<57>Fe implantation. In the studies we have reported an eminent enhancement of TMR effect by changing the relative amount of ^<57>Fe and ^<59>Co ions implanted in Al_2O_3 matrices with an energy of 100 keV and presented the largest MR ratio at room temperature among the values reported in the Fe-, Co-, and FeCo granular films.Furthermore, the implantation of ^<57>Fe and ^<63>Cu ions was performed at room temperature up to a total dose of 1.5×10^<17> ions/cm^2 with projectiles energies of 74-105 keV. It is shown by the measurements of CEMS and glancing angle X-ray diffraction (GXRD) that Fe implantation into SiO_2 substrate results in the dissolution of Si atoms into the precipitated iron nano-clusters. Furthermore, it is shown that the addition of Cu ions into both Fe/Al_2O_3 and Fe/SiO_2 granules promotes the transition from superparamagnetic to ferromagnetic states, indicating the formation of metastable Fe-Cu alloy nanoclusters. Less