Synthesis, structural and magnetic properties of the nanocomposite Fe63B23Nd7Y3Nb3Cr1 magnets

The Fe₆₃B₂₃Nd₇Y₃Nb₃Cr₁ nanocomposite magnets in the form of sheets have been prepared by copper mold casting technique. The phase evolution, crystal structure, microstructural and magnetic properties have been investigated in the as-cast and annealed states. The as-cast sheets show magnetically soft behaviors which become magnetically hard by thermal annealing. The optimal annealed microstructure was composed of nanosize soft magnetic α-Fe (19-29 nm) and hard magnetic Nd₂Fe₁₄B (45-55 nm) grains. The best hard magnetic properties such as intrinsic coercivity, _jH_c of 1119 kA/m, remanence, B_r of 0.44 T, magnetic induction to saturation magnetization ratio, M_r/M_s=0.61 and maximum energy product, (BH)_max of 55 kJ/m³ was obtained after annealing at 680 °C for 15 min. The annealing treatment above 680 °C results in non-ideal phase grains growth, which degrade the magnetic properties.     

STM investigations of Au(1 1 1) electrodes coated with vitamin B12 derivatives

Vitamin B₁₂ derivatives immobilized at flame-annealed Au(1 1 1) electrode surfaces have been investigated in close correlation with their structural properties and spatial arrangement at the electrode substrate by scanning tunneling microscopy (STM) in air and in aqueous 0.1 M NaClO₄ solution. The investigated compounds were symmetrical (B₁₂C₁₀S-SC₁₀B₁₂) and nonsymmetrical (B₁₂C₁₀S-SC₁₀) dialkyl disulfide derivatives of vitamin B₁₂, attached to the electrode surfaces by the S-Au bond. The ex situ and in situ STM experiments show the formation of a surface layer, whose packing density and structure is presumably controlled by the spatial arrangement of the large cobyrinate head groups. In presence of the symmetrical B₁₂ compound, a disordered surface layer is observed. Voltammetric investigations show that, in 0.1 M NaClO₄, this layer becomes unstable at potentials approximately ? −1000 mV vs. MSE and is almost completely removed at more negative potentials. The STM imaging properties of the nonsymmetrical B₁₂ surface layer show a significant dependence on the tunneling distance. In particular, at small tunneling distances, a highly regular hexagonal surface pattern is observed that suggests strongly the presence of an ordered surface assembly. Modeling of the B₁₂ head group has been performed to provide information for a structure-related interpretation of the high-resolution STM images. The investigations are first STM results obtained at such B₁₂ modified electrodes.     

L10 FePt thin films with [0 0 1] crystalline growth fabricated by SiO2 addition—rapid thermal annealing and dot patterning of the films

FePt films that have a high degree of order S in their L1₀ structure (S>0.90) and well-defined [0 0 1] crystalline growth perpendicular to the film plane were fabricated on thermally oxidized Si substrates by the addition of an oxide and successive rapid thermal annealing (RTA). The mechanism of L1₀ ordering and [0 0 1] crystalline growth perpendicular to the film plane arising through the oxide addition and RTA process is also discussed. The L1₀ ordering (S>0.90) and the [0 0 1] crystalline growth were achieved by (1) lowering the activation energy due to in-plane tensile stress and the initiation of L1₀ ordering at a low temperature, (2) [0 0 1] crystalline growth through in-plane tensile stress, and (3) enhancement of atomic diffusion via the addition of an oxide and the resultant lowering of the ordering temperature. Effect (1) was observed in the case of SiO₂ addition, effect (2) was generally observed in the case of oxide addition and the RTA process, and effect (3) was prominent in the case of ZnO addition. With the addition of ZnO, the L1₀ ordering started at below 400 °C and was completed at 500 °C. Finally, dot patterns were successfully fabricated down to a diameter of 15 nm using electron beam lithography, and the magnetic state of the dot pattern was observed by magnetic force microscopy.     

微观相场法模拟Ni75Al5.3V19.7 中L12和D022结构反位缺陷的演化

运用微观相场法研究Ni₇₅Al_5.3V_19.7合金沉淀过程中L1₂结构和D0₂₂结构反位缺陷发现：在沉淀初期,L1₂结构反位缺陷Al_Ni,V_Ni,Ni_Al,D0₂₂结构反位缺陷V_Ni,Al_Ni关键词： 微观相场 反位缺陷 L1₂结构')" href="#">L1₂结构 D0₂₂结构')" href="#">D0₂₂结构