Search

Processes of high-energy ball milling of SmCo 5 alloys were compared for three single-liquid environments without using additional surfactants. Both coarsely grained as-cast and nanocrystalline pre-milled SmCo 5 precursors showed tendency toward formation of thin flakes if milled in polar liquids (acetone and ethanol) in a marked contrast to milling in non-polar heptane. CaF 2 dielectric powder added prior to milling in the polar liquids tends to become attached on the flake surfaces. Milling in heptane in the presence of CaF 2 produces flake-like SmCo 5 particles which with increasing the milling time are found to incorporate an increasing amount of CaF 2 . The SmCo 5 —5 wt% CaF 2 mixtures milled for the optimum time in both the polar and non-polar liquids were successfully hot-pressed into laminated composite magnets having intrinsic coercivity of 25–30 kOe, maximum energy product of approximately 6.5 MG Oe and electrical resistivity of 500–600 μΩ cm, which is more than 7 times the resistivity of conventional Sm–Co magnets.

We report the fabrication of planar microstripline reciprocal phase shifter using a bulk Yttrium Iron Garnet (YIG) material. The propagation direction of the microstripline and magnetization direction of the YIG is collinear, and the length of the microstripline and the YIG was 50 mm in length. The proposed design shows large differential phase shifts of 100 degrees for applied magnetic fields varying from 0 to 0.56 times 104 A/m over the frequency range of 1.2 GHz between 5.4 GHz and 6.6 GHz. The average insertion loss, ~ 2.5 dB, was measured to have a 20% bandwidth at 6 GHz. The planar phase shifter presented here demonstrates a compact design, low loss, and an especially large phase shift with a relatively small bias field.

Sc is substituted for Fe in Ba M-type hexaferrite to reduce the anisotropy field and shift the ferromagnetic resonance (FMR) frequency to below 20 GHz. We have produced pure phase BaFe11 ScO19 powders having a platelet microstructure. These materials are pressed under an applied magnetic field of 95.5times10 5 A/m. Resulting compacts are sintered and are shown to have a clear uniaxial anisotropy with the c-axis perpendicular to the surface plane. Hysteresis loops display a squareness of 0.83 with a coercivity of ~186 kA/m. The X-band FMR power derivative linewidth is measured to be 79.6 kA/m

Monodisperse bimetallic Pd–Co nanoparticles were prepared via a thermal decomposition of cobalt carbonyl using palladium seeds at the Pd/Co molar ratios 0.5%, 1%, and 5%. The heterogeneously nucleated nanoparticles without any size-selective precipitation are sufficiently uniform to self-assemble into ordered arrays. The as-synthesized nanoparticles are each a single crystal with a complex cubic structure called e -Co. The presence of Pd seeds seems to improve the stability of Co nanoparticles against oxidation based on the results from time-dependent magnetization measurement.

Mn ferrite (MnFe(2)O(4)) nanoparticles, having diameters from 4 to 50 nm, were synthesized using a modified co-precipitation technique in which mixed metal chloride solutions were added to different concentrations of boiling NaOH solutions to control particle growth rate. Thermomagnetization measurements indicated an increase in Neel temperature corresponding to increased particle growth rate and particle size. The Neel temperature is also found to increase inversely proportionally to the cation inversion parameter, delta, appearing in the formula (Mn(1-delta)Fe(delta))(tet)[Mn(delta)Fe(2-delta)](oct)O(4). These results contradict previously published reports of trends between Neel temperature and particle size, and demonstrate the dominance of cation inversion in determining the strength of superexchange interactions and subsequently Neel temperature in ferrite systems. The particle surface chemistry, structure, and magnetic spin configuration play secondary roles.

Disordered nanocrystalline Ni3Fe alloy was prepared by mechanical alloying of elemental powders. X-ray diffractograms show the formation of Ni3Fe single phase. The chemical composition and morphology of the powder have been obtained by using EDAX and SEM analysis respectively. While the saturation magnetisation decreases with milling time, the coercivity increases. The width of the hyperfine field distributions obtained from Mossbauer studies shows that the alloy is highly disordered Atomic ordering is found to take place at a faster rate compared to that in the bulk alloy. (C) 1999 Acta Metallurgica Inc.

We report here the magnetocaloric effect (MCE) in bulk and nanostructured gadolinium iron garnets (Gd3Fe5O12). When compared with the bulk counterpart, the magnitude of the MCE is smaller for nanostructured samples with an average grain size of 50nm, but increases when the grain size decreases to 35nm. For the bulk sample, the MCE curves show a broad peak at 35K; this peak is found to shift to lower temperatures for the nanostructured samples. The origin of the MCE peak for the bulk sample is associated with the intrinsic magnetic frustration and the ferromagnetic ordering of the Gd sublattice below 90K, while for nanostructured garnets it is additionally ascribed to the surface spin disorder and particle blocking effects. While blocking is detrimental to achieving large MCE, surface spin disorder is found to enhance it under high applied fields. (Some figures in this article are in colour only in the electronic version)