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The ion implantation of nearly equal doses of Co and Pt into a single-crystal Al2O3 host followed by thermal annealing leads to the formation of nanoparticles whose phase, structure and physical properties are strongly dependent on the annealing environment. Annealing in ultrahigh-vacuum conditions results in a mixture of phases including CoPt3 and CO3O4 and possibly Co.

Electron microscopy, x-ray diffraction and superconducting quantum interference device magnetometry are used for examining the FePt and Fe3O4 nanotubes produced by hydrogen reduction in nanochannels of porous alumina templates. Fe3O4 tubes are formed by a thermally decomposed Fe nitrate solution at 250 degrees C that is reduced in hydrogen for 2.5 h at the same temperature.

The magnetic properties and switching behavior of anisotropic magnetic nanodots are examined. A strong interdot interaction is observed in dot separations of less than 50 nm resulting in a probable controlled switching of neighboring dots.

Simulations of the magnetization curves for assemblies of nanoscale Fe inclusions in a nonmagnetic host are presented. It is shown that, because of magnetostatic interactions, the magnetization curves will lack anisotropy.

Electron microscopy and magnetic properties of Fe-Co alloy catalysts used for the synthesis of vertically aligned carbon nanofiber (VACNF) are described. The nanofibers are grown by dc plasma-enhanced vapor deposition (PECVD) and the magnetic properties are measured with a superconducting quantum interference device based magnetometer.

The properties of FePt nanoparticles formed by the implantation of Fe + Pt into c-axis-oriented Al2O3 single crystals followed by thermal annealing are shown to be strongly dependent on the annealing environment. The results obtained by sequential annealing of Fe + Pt implanted samples in reducing environments followed by annealing in an oxidizing environment suggest that equilibrium, rather than kinetics, effects are responsible for the observed microstructures.

Model calculations and micromagentic simulations are used for examining the magnetic ground state and the magnetization reversal of aspherical nanoparticles. No domains are present in the dots at the lower end of the size and thickness range and large particles are multidomain with nearly complete flux closure and complex reversal behavior.

A model developed by Sorge et al. in which Fe nanocubes were embedded in a yttria-stabilized zirconia (YSZ) matrix with a packaging fraction of about 10% is discussed. It is shown that dipole-dipole interactions are dominating factor in dictating the magnetic properties of this system and anisotropies play a negligible role.

Oriented Fe(sub 1-x)Pt(sub x) nanoparticles have been formed in single-crystal A1(sub 2)O(sub 3) host matrices by the sequential implantation of Fe and Pt ions followed by thermal annealing. Fe(sub 1-x)Pt(sub x) nanoparticles covering a wide range of alloy compositions have been formed in A1(sub 2)O(sub 3) single crystals by ion-beam synthesis.

A study was conducted, using the magnetic force microscopy (MFM), to investigate the properties of ferromagnetic FePt nanoparticles produced by the implantation of Fe and Pt ions into single-crystal Al2O3, or fused SiO2 followed by thermal processing. The result demonstrates that MFM can detect magnetism in nanosized particles that are situated several hundred nm below the sample surface.

Abstract: The fabrication and magnetism of L10 nanostructures with different shapes (such as nanoparticles and nanotubes) is investigated. These nanostructures are produced by hydrogen processing and focused ion beam milling. The structures exhibit interesting reversal modes and are of present or potential interest for sensors and imaging, as well as magnetic recording. [Copyright &y& Elsevier]

FePt and Fe[sub 3]O[sub 4] nanotubes are produced by hydrogen reduction in nanochannels of porous alumina templates and investigated by electron microscopy, x-ray diffraction analysis, and magnetic measurements. Loading the templates with a Fe chloride and Pt chloride mixture followed by hydrogen reduction at 560 °C leads to the formation of ferromagnetic FePt nanotubes in the alumina pores. Using a Fe nitrate solution, thermally decomposed at 250 °C and reduced in hydrogen for 2.5 h at the same temperature, yields Fe[sub 3]O[sub 4] tubes. The length of the nanotubes is about 50 μm and their diameters range from about 150 to 220 nm, depending on the thickness of the template film and the pore diameter distribution. Reflecting the different magnetocrystalline anisotropies of the compounds, the coercivities range from 0.61 kOe for Fe[sub 3]O[sub 4] to 20.9 kOe for FePt. The hysteresis is explained in terms of a tubular random-anisotropy model, which yields a diameter and anisotropy dependent transition from a curling-type mode (Fe[sub 3]O[sub 4]) to a localized mode (FePt). © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Abstract: Magnetization processes in particulate L10 FePt nanostructures are investigated by model calculations and numerical simulations. The systems considered include anisotropic nanograins embedded in non-magnetic matrix; randomly oriented nanoclusters embedded in a C matrix, and nanocomposites of FePt particles in a semi-hard matrix. The reversal mechanisms depend on both intra- and intergranular features. Quasi-coherent rotation dominates the reversal in weakly-coupled granular magnets, but interface imperfections yield a disproportionately strong coercivity reduction. Strong intergranular exchange leads to a transition to a discrete pinning regime, which is accompanied by a coercivity maximum. [Copyright &y& Elsevier]

Ion implantation followed by thermal processing has been used to synthesize nanoparticles of cobalt–platinum (Co–Pt) alloys in single-crystal Al2O3. Several phases, including CoPt in the L10 structure, Co3Pt, and CoPt3 that has the L12 structure, are selectively formed by varying the atomic ratio of implanted Co and Pt. These alloys are crystallographically oriented with respect to the host Al2O3 matrix, exhibiting multiple distinct orientations. Rutherford backscattering and X-ray diffraction have been used to study the influence of the processing conditions, including temperature and dose, on the formation of the alloys. The degree of chemical ordering in the L10 and L12 phases is not high and it is not improved significantly with long annealing times. Magnetization studies have been conducted using a SQUID magnetometer. Coercivities as high as 14.2 kOe (9.7 kOe) at 5 K with the field normal (parallel) to the surface have been measured, and they remain significant at room temperature and above. The coercivity is a function of the Pt fraction in the alloy. [Copyright &y& Elsevier]