Er Liu

Investigation on Spin Dependent Transport Properties of Core-Shell Structural Fe 3 O 4 /ZnS Nanocomposites for Spintronic Application

The core-shell structural Fe3O4/ZnS nanocomposites with controllable shell thickness were well-fabricated via seed-mediate growth method. Structural and morphological characterizations reveal the direct deposition of crystalline II-VI compound semiconductor ZnS shell layer on Fe3O4 particles. Spin dependent electrical transport is studied on Fe3O4/ZnS nanocomposites with different shell thickness, and a large magnetoresistance (MR) ratio is observed under the magnetic field of 1.0 T at room temperature and 100 K for the compacted sample by Fe3O4/ZnS nanocomposites, which is 50% larger than that of sample with pure Fe3O4 particles, indicating that the enhanced MR is contributed from the spin injection between Fe3O4 and ZnS layer.

Texture induced magnetic anisotropy in Fe3O4 films

This letter reports a free energy density model for textured films in which the related physical concept and expression of magneto-texture anisotropy energy are presented. The structural characterization and out-of-plane angular dependence ferromagnetic resonance of strongly textured Fe3O4 films were systematically investigated. We found that the typical free energy density model for polycrystalline film cannot be applied to the textured films. With the introduction of magneto-texture anisotropy energy in the free energy density model for thin films, we simulated and quantitatively determined the competing anisotropies in (111)-textured Fe3O4 films.

Enhancement of magnetic moment in ZnxFe3−xO4 thin films with dilute Zn substitution

Highly (111)-textured ZnxFe3−xO4 thin films were grown by pulsed laser deposition on silicon substrates. The spin and orbital magnetic moments of the ZnxFe3−xO4 thin films have been obtained by X-ray magnetic circular dichroism (XMCD) and sum rule analysis. The total magnetic moments thus extracted are in good agreement with the values obtained by vibrating sample magnetometer. Both the unquenched orbital moment and the ratio of orbital-to-spin moment first increase significantly with increasing Zn substitution at a low concentration range ( 0≤x≤0.1), and then decrease at a higher concentration (x = 0.3). The underlying site-specific doping mechanisms involved here have been elucidated by detailed analysis of the XMCD of ZnxFe3−xO4 films. Our work demonstrates a practical means to manipulate the spin-orbit coupling in the ZnxFe3−xO4 thin films via Zn impurity doping.

Influence of Au capping layer on the magnetic properties of ultrathin epitaxial Fe3O4/GaAs(001) film

The effect of the Au capping layer on the magnetic anisotropies and molecular magnetic moment of ultrathin epitaxial Fe3O4 films on GaAs(100) substrate was studied by MO Kerr effect, superconducting quantum interference device, and Ferromagnetic resonance, respectively. The films with and without capping layers show a predominant in-plane uniaxial magnetic anisotropy and a minor fourfold anisotropy. The Au capping layer was found to increase significantly the uniaxial magnetic anisotropy related to the magnetoelastic interactions at the Au/Fe3O4 interface, and unexpectedly reduce saturation molecular magnetization due to the interfacial diffusion between Au layer and Fe3O4 layer.

Spin transport in CH3NH3PbI3

Organometal trihalide perovskites with the general formula (CH3NH3)PbX3 (X is Cl, I and/or Br) have a composition dependent tunable band gap and long electron–hole diffusion length, which is not only being hotly studied for usage in hybrid solar cells, but also has potential application in organic spintronics. In this work, we prepared CH3NH3PbI3-coated Fe3O4 granular films. CH3NH3PbI3 behaves effectively as a spacer to decouple the Fe3O4 particles and spin-preserved transporting matrix. The magnetoresistance of Fe3O4 particles has been significantly enhanced after CH3NH3PbI3 coating, which is about −6% at 300 K and −10.8% at 150 K under a magnetic field of 10 kOe, about 3 times larger than the values of pure Fe3O4 (−1.9% at 300 K and −3.4% at 150 K).

Inverse magnetoresistance in single layer Fe 3 O 4 film

Half-metallic magnetite with high spin polarization at the Fermi level has always been an ideal candidate for spin dependent transport study, and understanding of the magnetic transportation property of Fe₃O₄ becomes a critical issue for its future applications in spintronics. Generally the resistance of Fe₃O₄ decreases (negative MR) when applied in a magnetic field as the conduction in Fe₃O₄ is attributed to a small polaron hopping mechanism between Fe²⁺ ions and Fe³⁺ ions in oxygen ions octahedral sites, and the applied field is suggested to broaden the polaronic band leading to enhanced conduction. Previous studies on magnetic transportation of Fe₃O₄ film also confirm its negative MR effect, and positive MR effect is only observed in a few specific structures such as TiN/ Fe₃O₄ superlattices, magnetic tunnel junctions with Fe₃O₄ electrode, the increase of resistance after application of magnetic field for these system is ascribed to the spin selective quantum confinement effects in the heterostructure, which refer to the extrinsic structures instead of the intrinsic magnetic transportation property of magnetite film. However, in our recent studies, an anomalous positive magnetotransport behavior is demonstrated on high oriented Fe₃O₄ film grown on Si substrate at high temperature, and the inverse MR effect is believed to be highly correlated to the strong orientation of Fe₃O₄ film.

Investigation on transformation of spindle-like Fe3O4 nanoparticles from self-assembling α-Fe2O3

Porous monodisperse spindle-like α-Fe2O3 nanomaterials are first synthesized successfully by a hydrothermal method, and then the as-prepared nanoparticles are annealed at different temperatures under various atmospheres to achieve the spindle-like Fe3O4 nanoparticles. The evolution of the features of nanoparticles, including the changes of the structures and microstructures as well as the magnetic properties, during the reduction process has been investigated by using the Raman spectrum and Mossbauer spectrum. Our research reveals that the α-Fe2O3 nanoparticles annealed by covering of the C powder become a mixture of α-Fe2O3 and Fe3O4 in the range of annealing temperature from 300 °C to 800 °C. With reduced atmospheric H2, spindle-like α-Fe2O3 nanoparticles are transferred to mixture of α-Fe2O3, Fe3O4 and Fe as temperature increases. They are also converted from a typical rhombohedral structure to a cubic α-Fe phase at 500 °C. Finally, with the atmosphere of H2/Ar (5%/95%), a pure Fe3O4 phase, and its exc...

The magnetic properties of well-aligned nickel nanochains synthesized by magnetic field-induced assembly approach

Highly uniform one-dimensional Ni chains with controllable diameters and lengths have been synthesized at 70 °C by a hydrothermal process under a 0.35 T induced magnetic field. The diameter of the spheres in the magnetic Ni chains is adjusted from 80 nm to 1000 nm with the chain length changed from 1.2 μm to 50 μm by varying the concentration of ethylene glycol and potassium hydroxide in the solution. The Ni chains with different length-to-diameter aspect ratio show the different particle shape and interparticle spacing. Magnetic hysteresis loop measurements demonstrate a uniaxial magnetic anisotropy (UMA) on the coercivity (Hc), and saturation field (Hs). The ferromagnetic resonance (FMR) shows that the difference between demagnetizing fields in the direction of easy and hard increases with increasing the length-to-diameter aspect ratio of nanochains, which is close to then that in Hs. From FMR measurements and theoretical simulation, the difference of the demagnetizing field between the length and width...

Facile synthesis of one dimensional core–shell structural Fe 3 O 4 /ZnS nanocomposites

We demonstrate that 1D chain-like Fe3O4/ZnS nanocomposites with core shell structure can be well synthesized by a facile seed mediated growth method, which employs double coating process to enhance the surface activity of Fe3O4 chains for the formation of crystalline ZnS layer. Morphology and structure characterizations reveal the well-defined phases and direct coating of crystalline ZnS shell on Fe3O4 core, in spite of their large lattice mismatch. The composites show large saturation magnetization and good fluorescence properties, which might pave the way for their applications in semiconductor spintronics.

Magnetocrystalline anisotropy in textured Fe 3 O 4 film

The magnetic anisotropies are one of the dominating factors affecting the behavior of magnetic materials, which is profoundly evident in magnetic ultrathin films, and significant in the application of information storage and magnetic sensor field. Extensive studies of magnetic anisotropies in various films have been carried out. It is well known that the contribution of magnetocrystalline anisotropy is negligible in isotropic polycrystalline films while essential in single-crystal films. However, in textured film, a polycrystalline film composed of nanograins with the near same lattice orientation, the competing interactions between magnetocrystalline and other anisotropy is still an open issue. The quantitative investigations on the contribution of magnetocrystalline anisotropy in the textured film are rarely reported. In this paper, the expression of magnetocrystalline anisotropy energy in textured film (texture anisotropy energy) is given, and angle-resolved FMR studies on the textured Fe3O4 film is also presented.