Interfacial interaction in Fe/MgO/Fe magnetic tunneling junctions

We present a study on interfacial structures and tunneling magnetoresistance (TMR) in Fe/MgO/Fe junctions using a MgO(111) film with {100} facets. It is shown using X-ray photoelectron spectroscopy that a FeO layer occurs at MgO/Fe rather than Fe/MgO interface, which could be used to tune the TMR effect. At the Fe/MgO interface, such a change in electronic structure is attributed to the band bending associated with a change in thickness of Fe films. The present study provides a new understanding on the Fe/MgO/Fe interfacial behavior and metal/oxide barriers involving electron transport.     

Fe3Si formation in Fe–Si diffusion couples

Two different types of bulk diffusion couples for the Fe–Si system, i.e. Fe/Si and Fe/Fe3Si, have been studied, with emphasis placed on the formation and growth of Fe3Si. Results indicate that Fe3 Si forms initially in Fe/Si couples, followed by FeSi and then FeSi2. Fe3Si has a wide range of stoichiometry, from 10–25 at% Si; however, only stoichiometric Fe3Si appeared in Fe3Si diffusion layers of Fe/Si couples. Off-stoichiometric Fe3Si formed in Fe3Si/Fe couples. The free energy of Fe3Si and Fe–Si affinity are used to explain Fe3Si formation behaviour and the atomic diffusion mechanism in the Fe3Si lattice. © 1998 Kluwer Academic Publishers     

Effects of interfacial structure on the magnetic properties of ultrathin Fe/Pt(111) films with Ag buffer layer

For Fe/Pt(111) grown at 180 K, the easy axis of magnetization changes from out-of-plane to in-plane while the surface structure changes from fcc(111) to bcc(110). The Curie temperature for 1 ML Fe/Pt(111) is close to room temperature. After insertion of submonolayer Ag, no significant change for the Curie temperature is observed. By thermally annealing Ag/Pt(111) at 550 K to form a Ag-Pt surface alloy, we demonstrate that the Curie temperature of the deposited Fe films is elevated to be higher than room temperature. For an ultrathin Fe/Ag/Fe/Pt(111) sandwich system, the strong interaction between the two Fe layers is superior due to the effect of the double Fe/Ag interfaces. This causes that the easy axis of the magnetization switches back to the in-plane direction during the deposition of Fe overlayer on the surface of a Ag/Fe/Pt(111) film.     

Large scale synthesis of FeS coated Fe nanoparticles as reusable magnetic photocatalysts

The FeS coated Fe nanoparticles were prepared by using high temperature reactions between the commercial Fe nanoparticles and the S powders in a sealed quartz tube. The simple method developed in this work is effective for large scale synthesis of FeS/Fe nanoparticles with tunable shell/core structures, which can be obtained by controlling the atomic ratio of Fe to S. The structural, magnetic and photocatalytic properties of the nanoparticles were investigated systematically. The good photocatalytic performance originating from the FeS shell in degradation of methylene blue under visible light and the high saturation magnetization originating from the ferromagnetic Fe core make the FeS/Fe nanoparticles a good photocatalyst that can be collected and recycled easily with a magnet. An exchange bias up to 11 mT induced in Fe by FeS was observed in the Fe/FeS nanoparticles with ferro/antiferromagnetic interfaces. The enhanced coercivi-ty up to 32 mT was ascribed to the size effect of Fe core.     

Degradation of C.I. Reactive Red 2 (RR2) using ozone-based systems: comparisons of decolorization efficiency and power consumption

This study investigated the decolorization efficiency of C.I. Reactive Red 2 (RR2) in O3, O3/H2O2, O3/Fe3+, O3/H2O2/Fe3+, UV/O3, UV/O3/Fe3+, UV/O3/H2O2 and UV/O3/H2O2/Fe3+ systems at various pHs. The effective energy consumption constants and the electrical energy per order of pollutant removal (EE/O) were also determined. The experimental results indicated that the energy efficiency was highest at [H2O2]0=1000mg/l and [Fe3+]0=25mg/l. Accordingly, the H2O2 and Fe3+ doses in the hybrid ozone- and UV/ozone-based systems were controlled at these values. This work suggests that the dominant reactant in O3, O3/Fe3+ and O3/H2O2 systems was O3 and that in the O3/H2O2/Fe3+ system was H2O2/Fe3+. The experimental results revealed that the combinations of Fe3+ or H2O2/Fe3+ with O3 at pH 4 and of H2O2 or H2O2/Fe3+ with UV/O3 at pH 4 or 7 yielded a higher decolorization rate than O3 and UV/O3, respectively. At pH 4, the EE/O results demonstrated that the UV/O3/H2O2/Fe3+ system reduced 85% of the energy consumption compared with the UV/O3 system. Moreover, the O3/H2O2/Fe3+ system reduced 62% of the energy consumption compared with the O3 system. At pH 7, the EE/O results revealed that the UV/O3/H2O2/Fe3+ system consumed half the energy of the UV/O3 system.     

Fe/V多层膜中亚稳结构Fe的形成及其磁学性能

采用电子束蒸镀的方法,通过改变多层膜的周期结构,成功地制备出具有不同晶格常数的bcc亚稳结构铁相的Fe/V多层膜,并研究了亚稳结构铁相形成对其磁性影响的规律.实验结果表明,多层膜中Fe与V层均由纳米晶粒组成.Fe层厚度小于2nm时,受多层膜界面自由能作用,Fe与V相互准外延生长,多层膜由点阵常数一致的体心立方相组成,其点阵常数随样品V/Fe层厚度比的增大而增加.多层膜平均原子磁矩随铁或钒层厚度的改变发生明显变化:当钒层厚度固定为6nm时,铁原子磁矩随铁层厚度的增加逐渐下降,在2nm处出现极小值后又随铁层增厚而回升;对于铁层厚度固定为1.6nm的样品,磁矩在钒层厚度为3nm时出现极大值.     

Fe/Al2O3复合材料的制备和性能

用石墨埋烧方法制备Fe/Al₂O₃复合材料,对其力学性能和微观结构进行了分析。结果表明:Fe/Al₂O₃复合材料的弯曲强度与断裂韧性均随Al₂O₃含量的升高先升高后降低,当Al₂O₃含量（质量分数）为70%时,其弯曲强度与断裂韧性分别达到602.49 MPa和9.33 MPa·m¹/2,其硬度随Al₂O₃含量先降低后升高。在烧结过程中在Fe颗粒周围形成一种成分为FeO与FeAl₂O₄的壳体,在壳体与Fe颗粒之间存在微裂纹缺陷。壳体的形成和壳体与金属颗粒间的微裂纹钝化了外部应力,从而提高了复合材料的韧性。     

纳米金磁颗粒的组装法制备及其核酸分离性能

以丙烯酰胺为单体,采用原位聚合法制备了Fe3O4/聚丙烯酰胺纳米磁粒(Fe3O4/PAM);利用胺基与金的相互作用,借助自组装法在Fe3O4/PAM表面组装金胶体制备了草莓型纳米金磁颗粒(Fe3O4/PAM/Au);用TEM、VSM、UV-vis对其进行了表征,并考察了表面修饰核酸探针的金磁颗粒对核酸靶分子的分离能力。结果表明,Fe3O4/PAM/Au粒子的粒径为36～56nm,具有超顺磁性,饱和磁化强度为31.2emu/g,分散在磷酸盐缓冲液中的Fe3O4/PAM/Au完全磁分离的时间为6min。修饰核酸探针的Fe3O4/PAM/Au粒子可以借助核酸杂交作用分离核酸靶分子,分离能力为118pmol/mg。     

90°coupling in (Fe/Cr/Fe)AFM/Cr/Fe system epitaxially grown on GaAs(0 0 1)

Single-crystalline (Fe/Cr/Fe)_AFM/Cr/Fe structures were epitaxially grown on atomically flat GaAs(0 0 1). Choosing the same thickness of the antiferromagnetically (AFM) coupled Fe layers in the bottom (Fe/Cr/Fe)_AFM structure, their net magnetization is balanced to zero, in particular up to a spin-flop transition when the field is applied along the [1 1 0] direction. For the Cr thicknesses at which the top Fe layer is weakly magnetically coupled to the bottom (Fe/Cr/Fe)_AFM structure, at low fields, the magneto-optical Kerr effect and/or SQUID signal from the sample corresponds to the top Fe layer only. An influence of the Cr spin structure on the magnetization reversal in the Fe layer is reported. In particular, a strong increase of coercivity (by a factor of 12) is found at low temperatures. A 90° coupling is detected which affects the minor loops measured along the [−1 1 0] and [1 0 0] directions.     

Fe元素对Nb 16Si原位复合材料显微组织及室温力学性能的影响

采用真空非自耗电弧熔炼方法制备了Nb-16Si-xFe原位复合材料(x = 2, 4, 6, 原子分数(%), 分别简称为2Fe、4Fe、6Fe合金), 研究了Fe含量对Nb-16Si合金的显微组织与室温力学性能的影响。结果表明: 铸态及热处理态(1350 ℃真空退火100 h) 2Fe和4Fe合金主要由Nb基固溶体(Nb_SS)、Nb₃Si和Nb₄FeSi三相组成, 随着Fe含量的增多, Nb₃Si含量减少, 而Nb₄FeSi含量增加, 6Fe合金仅由Nb_SS和Nb₄FeSi两相组成; 热处理后Nb_SS上有细小的硅化物析出; Nb-16Si合金中加入Fe元素后所生成的新相Nb₄FeSi是一个硬脆的硅化物相, 其显微硬度和室温断裂韧性 分别为HV 1110和1.22 MPa·m1/2; 随着Fe含量由2%提高到6%, 热处理态Nb-16Si-xFe合金的室温 断裂韧性呈略微下降趋势, 而硬度和压缩强度呈上升趋势。