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There are two main thrusts towards new permanent-magnet materials: improving extrinsic properties by nanostructuring and intrinsic properties by atomic structuring. Theory—both numerical and analytical—plays an important role in this ambitious research. Our analysis of aligned hard-soft nanostructures shows that soft-in-hard geometries are better than hard-in-soft geometries and that embedded soft spheres are better than sandwiched soft layers. Concerning the choice of the hard phase, both a high magnetization and a high anisotropy are necessary. As an example of first-principle research, we consider interatomic Mn exchange in MnAl and find strongly ferromagnetic intralayer exchange, in spite of the small Mn-Mn distances. [ABSTRACT FROM AUTHOR]

Nanostructured Mn3 - x Ga ribbons with x = 0, 0.4, 0.9 and 1.1 were prepared using arc-melting, melt-spinning and annealing. As-spun samples crystallized into hexagonal D019 and cubic L21 Heusler crystal structures based on the concentration of Mn in Mn3 - xGa. Upon vacuum-annealing the samples at 450 ^\circC for about 50 hours, both the hexagonal and cubic structures transformed into a tetragonal D022 structure. High-temperature x-ray diffraction and high-temperature magnetometry showed that the samples with low Mn content (Mn1.9 Ga and Mn2.1Ga) retain their tetragonal structure up to 850 K but the samples with high Mn concentrations (Mn2.6 Ga and Mn3.0Ga) undergo a structural phase transition from tetragonal to hexagonal phases around 800 K. The magnetic properties of Mn3 - x Ga ribbons were very sensitive to Mn concentration, where the magnetization and anisotropy energy increased and the coercivity decreased as x increased from 0 to 1.1. Although the Curie temperatures of Mn2.6 Ga and Mn3.0 Ga samples could not be determined because of the structural phase transition, the Curie temperature decreased with increasing x in Mn3 - xGa. The maximum magnetization of 57 emu/g (300 emu/cm^3) and the coercivity of 6.5 kOe were measured in the Mn1.9 Ga and Mn3.0Ga ribbons, respectively. [ABSTRACT FROM AUTHOR]

We fabricated exchange-coupled composite films with perpendicular anisotropy using nanograins of L10 FePt as a magnetically hard base layer and FePt : SiO2 as a relatively soft phase. The degree of anisotropy and nanostructure in the soft layer was controlled by varying the deposition temperature. Growth of the low-anisotropy layer followed the particulate structure of the base layer at deposition temperatures of 390°C or greater. Perpendicular coercivities were strongly dependent on both the anisotropy and thickness of the softer layer. [ABSTRACT FROM AUTHOR]

A simple approach combining pyrolysis and hydrogen reduction is formulated for making ferromagnetic-branched nanostructures called Co multipods. The CoO multipods (branched nanostructures) were produced through the pyrolysis of cobalt-oleate in octadecane at 280 °C with the presence of oleic acid under the protection of pure nitrogen. The angles between the nearest arms are 900. After the reduction of the branched CoO nanostructures in flowing hydrogen gas in a tubular oven at 290 °C, the CoO is reduced to pure cobalt with hexagonal crystal structure and the branched shapes are retained. Anisotropic magnetic properties were found for cobalt multipods on silicon substrates. [ABSTRACT FROM AUTHOR]

Highly textured (001) FePt:C nanocomposite thin films, deposited directly on thermally oxidized Si wafers, are obtained by multilayer deposition plus subsequent thermal annealing. Nanostructures, crystalline orientations, interactions, and magnetic properties are investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD), magnetic force microscopy, and magnetic measurements. The formation of the ordered L1o phase is confirmed by XRD, and only visible (001) peaks indicate a high degree of the (001) texture. TEM observation reveals that FePt grains are embedded in the C matrix and appear to be well isolated. The FePt grains are very uniform with average sizes about 5 um. [ABSTRACT FROM AUTHOR]