Shuyun Yu

Structural and magnetic properties of patterned perpendicular media with linearly graded anisotropy

L10-FePt thin films with linearly distributed anisotropy were fabricated by continuously varying substrate temperatures from 650 °C to 290 °C. An average ordering parameter S = 0.6 was obtained. The hysteresis loop has a clear bow-tie shape with low remanence and coercivity before patterning. The patterned nanopillar arrays exhibit an enhancement in both remanence and coercivity. Dynamic coercivity measurement shows that the nanopillar arrays with linearly graded anisotropy have a relatively small intrinsic coercivity and a relatively high value of the figure of merit. The switching field exhibits a narrow distribution, which indicates a strong coupling between soft and hard phases in nanopillar arrays with graded anisotropy.

Broad-Band FMR Linewidth of Co2MnSi Thin Films with Low Damping Factor: The Role of Two-Magnon Scattering*

The low Gilbert damping factor, which is usually measured by ferromagnetic resonance, is crucial in spintronic applications. Two-magnon scattering occurs when the orthogonality of the ferromagnetic resonance mode and other degenerate spin wave modes was broken by magnetic anisotropy, voids, second phase, surface defects, etc., which is important in analysis of ferromagnetic resonance linewidth. Direct fitting to linewidth with Gilbert damping is advisable only when the measured linewidth is a linear function of measuring frequency in a broad band measurement. We observe the nonlinear ferromagnetic resonance linewidth of Co2MnSi thin films with respect to measuring frequency in broad band measurement. Experimental data could be well fitted with the model including two-magnon scattering with no fixed parameters. The fitting results show that two-magnon scattering results in the nonlinear linewidth behavior, and the Gilbert damping factor is much smaller than reported ones, indicating that our Co2MnSi films are more suitable for the applications of spin transfer torque.

A facile way to synthesize rare-earth-free Mn–Bi@Bi magnetic nanoparticles

Rare-earth-free manganese bismuth (MnBi) is a promising candidate as an earth abundant permanent magnet for its large magnetocrystalline anisotropy and high energy density. A facile aqueous solution method was designed to synthesize MnBi@Bi nanoparticles, which exhibits a saturation magnetization of 2.37 emu g−1, the coercivity of 8 kOe at 5 K and superparamagnetism at 300 K. This processing approach eliminates severe synthesis equipment and makes it a versatile scalable strategy for preparing MnBi nanoparticles.

Ag-Decorated Fe3O4@SiO2 Nanorods: Synthesis, Characterization, and Applications in Degradation of Organic Dyes

Well-dispersed Ag nanoparticles (NPs) are successfully decorated on Fe3O4@SiO2 nanorods (NRs) via a facile step-by-step strategy. This method involves coating α-Fe2O3 NRs with uniform silica layer, reduction in 10% H2/Ar atmosphere at 450°C to obtain Fe3O4@SiO2 NRs, and then depositing Ag NPs on the surface of Fe3O4@SiO2 NRs through a sonochemical step. It was found that the as-prepared Ag-decorated magnetic Fe3O4@SiO2 NRs (Ag-MNRs) exhibited a higher catalytic efficiency than bare Ag NPs in the degradation of organic dye and could be easily recovered by convenient magnetic separation, which show great application potential for environmental protection applications.

Controlled synthesis of ferromagnetic MnSe x particles

The MnSe x (x = 1,2) nanoparticles were synthesized under hydrothermal condition, by reaction of the reduced selenium and Mn2+ ion in the presence of hydrazine and acetic acid. By precisely controlling the pH value of the solution, a series of MnSe x particles were synthesized. The structure and morphology of as-prepared particles were examined with x-ray diffractometer (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The average sizes of as-prepared particles varied from nanoscale to microscale with pH value increase. Furthermore, the nucleation and growth mechanism associated with pH values were discussed, which can be applied to the hydrothermal synthesis of metal chalcogenide in general. Finally, the optical and magnetic properties of as-prepared particles were measured. All as-made particles exhibit a ferromagnetic behavior with low coercivity and remanence at room temperature.

Novel Fe3O4@SiO2@Ag@Ni trepang-like nanocomposites: High-efficiency and magnetic recyclable catalysts for organic dye degradation*

A facile step-by-step approach is developed for synthesizing the high-efficiency and magnetic recyclable Fe3O4@SiO2@Ag@Ni trepang-like nanocomposites. This method involves coating Fe2O3 nanorods with a uniform silica layer, reduction in 10% H2/Ar atmosphere to transform the Fe2O3 into magnetic Fe3O4, and finally depositing Ag@Ni core-shell nanoparticles on the L-lysine modified surface of Fe3O4@SiO2 nanorods. The fabricated nanocomposites are further characterized by x-ray diffraction, transmission electron microscopy, scanning electron microscope, Fourier transform infrared spectroscopy, and inductively coupled plasma mass spectroscopy. The Fe3O4@SiO2@Ag@Ni trepang-like nanocomposites exhibit remarkably higher catalytic efficiency than monometallic Fe3O4@SiO2@Ag nanocomposites toward the degradation of Rhodamine B (RhB) at room temperature, and maintain superior catalytic activity even after six cycles. In addition, these samples could be easily separated from the catalytic system by an external magnet and reused, which shows great potential applications in treating waste water.