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

高剂量磁性离子注入绝缘氧化物制备的金属-绝缘体纳米复合层提供了诸如巨磁隧道结等诱人的结构。在100keV Fe~(++)离子注入的α-Al_2O_3单晶中观察到明显的隧道磁阻效应，注入层的磁阻比约为7~8%。所得结果约为射频溅射制备的Fe/Al_2O_3颗粒薄膜的两倍。此外，我们还成功地通过Fe和Co离子的顺序注入在Al_2O_3基质中合成了FeCo合金纳米团簇。在FeCo颗粒层中还发现，合金化导致了铁磁矩的增加。通过这些研究，我们获得了关于注入…聚集态的详细信息通过转换电子穆斯堡尔谱(CEMS)获得了更多的Fe离子。CEMS为这种表征提供了原子尺度上的高灵敏度和微观手段，特别是当它与质量选择的^&lt；57&gt；Fe注入相结合时。在这些研究中，我们报道了通过改变能量为100keV的Al_2O_3基片中^&lt；57&gt；Fe和^&lt；59&gt；Co离子的相对注入量来显著地增强TMR效应，并且在Fe、Co和FeCo颗粒膜中呈现了最大的室温MR比。此外，^&lt；57&gt；Fe和^&lt；63&gt；Cu离子的注入是在室温下进行的，总剂量达到1.5×10^&lt；17&gt；离子数/厘米^2，入射能量74-105keV。CEMS和掠射角X射线衍射仪的测量表明，Fe注入SiO_2衬底后，Si原子溶解为析出的Fe纳米团簇。此外，在Fe/Al_2O_3和Fe/SiO_2颗粒中添加铜离子促进了从超顺磁性到铁磁性的转变，表明亚稳Fe-Cu合金纳米团簇的形成。较少

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