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FePt/[Fe.sub.2]Pt bulk nanocomposite magnets are prepared by the spark plasma sintering of chemically synthesized FePt and [Fe.sub.3][O.sub.4] nanoparticles. It is shown that the pressure rather than temperature is effective in increasing the intergrain exchange when compared to temperature.

Chemical synthesis is used for preparing the FePt nanoparticles with controlled composition. The difference in Curie temperature between the heating and cooling thermomagnetic curves of the Fe-Pt alloys is attributed to the difference of [alpha] [left right double arrow] [gamma] phase transition temperature during heating and cooling.

Salt (NaCl)-matrix annealing, an easy-handling method is developed to produce monodisperse fct FePt nanoparticles. Important parameters of this method, such as salt-to-particle ratio, are carefully investigated and it is concluded that annealing at higher temperatures and extended time should be accompanied by a higher salt-to-FePt ratio in order to avoid sintering.

FePt nanocrystals are prepared by simultaneous reduction of platinum acetylacetonate and thermal decomposition of iron pentacarbonyl in solvents/surfactants and the shape control is realized by varying synthesis parameters. The as-synthesized FePt nanocrystals are transformed to the chemically ordered [L1.sub.0] structure upon heat treatment, which has displayed hard magnetic properties with coercivity as high as 25 kOe.

The state of the chemical ordering in a decahedral FePt nanoparticle is analyzed by using aberration corrected high resolution transmission electron microscopy. The image intensity oscillation from one atomic layer to another is interpreted as [L1.sub.0]-like chemical ordering, which has survived even in decahedral nanoparticles down to 3 nm size despite the possible surface effects.

The correlation between the recoil loop openness and the activation volume is analyzed for the Sm[Co.sub.5]/[alpha]-Fe nanocomposite powder material prepared by mechanical alloying. The large open area of the recoil loops for nanocomposite magnets is ascribed to the fact that low anisotropy in the [alpha]-Fe phase leads to unstable magnetization under thermal fluctuation.

The studies on magnetoelectric (ME) measurements on the core-shell sintered composites in the Pb(Zr, Ti)[O.sub.3]-Ni[Fe.sub.2][O.sub.4] (PZT-NF) system are reported. The results showed that the PZT-NF structure could provide a large magnitude of ME coupling over a wide bandwidth.

The salt-matrix annealing method is used for preparing the monodisperse [L1.sub.0]-FePt nanoparticles. The high thermal stability has resulted from carbon coating of the particles during salt-matrix annealing as a consequence of decomposition of surfactants.

The preparation of high density bulk FePt/[Fe.sub.3]Pt nanocomposite magents by high-pressure warm compaction of chemically synthesized FePt and [Fe.sub.3][O.sub.4 nanoparticles is demonstrated.

The microstructure, magnetic properties and easy axis alignment of chemically ordering FePt nanoparticles are studied. The results have shown the c-axis alignment for a monolayer of [L1.sub.0] FePt particles and the intensity of (200) electron diffraction (ED) has clearly shown twofold symmetry.