R. L. Wang

High-pressure synthesis of giant magnetostrictive PrxTb1−xFe1.9 alloys

PrxTb1−xFe1.9 (0⩽x⩽1) magnetostrictive alloys with cubic Laves phase have been synthesized by a high-pressure synthesis method. Crystal structure, magnetic properties, magnetocrystalline anisotropy, and the magnetostriction of PrxTb1−xFe1.9 (0⩽x⩽1) alloys are investigated. Composition anisotropy compensation is realized in Pr0.9Tb0.1Fe1.9 alloy, which shows low magnetocrystalline anisotropy and a large magnetostriction value (λ‖−λ⊥=1497ppm) at 13kOe at room temperature. These characters suggest that Pr0.9Tb0.1Fe1.9 alloy may be a promising candidate for magnetostriction application.

Chemical synthesis and magnetic properties of well-coupled FePt/Fe composite nanotubes.

A simple two-step hydrogen reduction method was used to synthesize FePt/Fe composite nanotubes. As the first step, L1(0) FePt nanotubes were prepared by heating a porous alumina template loaded with an alcohol solution of a Fe chloride and Pt chloride mixture in flowing hydrogen at 670 degrees C. Then, FePt/Fe composite nanotubes were obtained by reducing the alcohol solution of the Fe chloride within the formed FePt nanotubes at a lower temperature, namely 470 degrees C. Through changing the concentrations of initial alcohol solutions, the FePt:Fe atomic ratios of the composite nanotubes were easily adjusted and the magnetic properties were tuned accordingly. For (FePt)(100-x)/Fe(x) composite nanotubes with x ranging between 0 and 26 at.%, the hard and soft phases were well coupled and the coercivity was tunable over a large range (1.27-2.73 T). Furthermore, the marked interdiffusion between Fe and FePt, which usually exists in FePt-based composites fabricated by using conventional methods, was not observed in the formed composite nanotubes. This indicates the two-step hydrogen reduction method to be a promising route for synthesizing nanocomposites which are difficult to fabricate by using conventional methods due to the interdiffusion between different phases.

Composition anisotropy compensation and magnetostriction in Pr(Fe1-xCox)1.9 (0≤x≤0.5) cubic Laves alloys

Polycrystalline magnetostrictive alloys Pr(Fe1−xCox)1.9 (0⩽x⩽0.5) with cubic Laves phase were synthesized by high-pressure annealing. Measurements of Curie temperature, easy magnetic direction (EMD), and magnetostriction were made on these alloys. The EMD of the alloys rotates continuously from ⟨111⟩ for x=0.0 to ⟨110⟩ for x=0.3 and then shows a tendency to ⟨111⟩ with further increasing x. Two magnetostriction peaks at low fields are observed around x=0.2 and x=0.4 due to the lower anisotropy of these two alloys, which is consistent with the variation of EMD. This work demonstrates that the composition anisotropy compensation can be realized in Pr(Fe1−xCox)1.9 system.

Effects of annealing on the structure and magnetic properties of Fe27Co23Pb50 nanowire arrays

Ferromagnetic-nonmagnetic heterogeneous Fe27Co23Pb50 ternary metal nanowire arrays were successfully fabricated by alternating current electrodeposition into anodic alumina oxide (AAO) template. The effects of the different annealing temperatures (100, 200, 300, 400, 500, 600°C) on the structure and magnetic properties have been discussed. X-ray diffraction observations indicated that FeCo and Pb phases coexist for the as-deposited and annealed samples. Magnetic measurements indicate that the nanowire arrays have high perpendicular magnetic anisotropy with their easy axis parallel to the nanowire arrays. The coercivity and remanence ratio increases as the annealing temperature rises, reaches their maximum at 400°C, and then decreases as the annealing temperature rises further. The mechanism of the magnetic properties and magnetic variety should be attributed to the special structure of the nanowires∕AAO.

Fe48Co52 Alloy Nanowire Arrays: Effects of Magnetic Field Annealing

The effects of magnetic field annealing on the properties of Fe48Co52 alloy nanowire arrays with various interwire distances (Di = 30?60 nm) and wire diameters (Dw = 22?46 nm) were investigated in detail. It was found that the arrays best annealing temperature and crystalline structure did not show any apparent dependence on the treatment of applying a 3 kOe magnetic field along the wire during the annealing process. For arrays with small Dw or with large Di, the treatment of magnetic field annealing also had no obvious influence on their magnetic performances. However, such a magnetic field annealing constrained the shift of the easy magnetization direction and improved the coercivity and the squareness obviously for arrays with large Dw or with small Di. The difference in the intensity of the effective anisotropic field within the arrays was believed to be responsible for this different variation of the arrays magnetic properties after magnetic field annealing.

Mn substitution effect on the magnetic properties of PrFe1.9 alloy

Polycrystalline magnetostrictive alloys Pr(Fe1−xMnx)1.9 (0⩽x⩽0.2) were synthesized by high-pressure annealing. X-ray diffraction results show that all the samples exhibit cubic Laves phase with MgCu2-type structure. The lattice parameter increases with increasing Mn concentration while the Curie temperature decreases. The saturation magnetization decreases with increasing Mn concentration, which can be understood on the basis of the rigid band model. The magnetizations of the samples with x=0.05 and x=0.1 are easy to get saturated in comparison with that of the sample without Mn, which implies that small amount of substitution Mn for Fe can lower the magnetic anisotropy of the alloy. The saturation magnetostriction decreases monotonously with increasing Mn content, while the magnetostriction of the sample with x=0.1 shows a peak at low magnetic fields.