No abstract

Morphological control of FePt nanoparticles has been systematically studied. By varying synthetic parameters including precursors, solvents, amount of surfactants, and heating rate of the solution, the particle size from 2 to 9 nm can be tuned with 1 nm accuracy. While most particles are spherical in shape, cubic particles can be obtained when particles are greater than 7 nm. Rod-shape nanoparticles have also been obtained. The as-synthesized nanoparticles are found to be superparamagnetic at room temperature and their blocking temperature is size dependent that increases with particle size. After annealing in a reducing atmosphere, the nanoparticles form hard magnetic films with ordered fct structure and high coercivity up to 2.7 T.

Mixed spinel hydrophobic ZnxFe1-xO x Fe2O3 (up to x = 0.34) nanoparticles encapsulated in polymeric micelles exhibited increased T2 relaxivity and sensitivity of detection over clinically used Feridex.

Bimagnetic FePt/ Fe 3 O 4 nanoparticles with core/shell or heterodimer structure have been prepared using a sequential synthetic method. The dimension of both FePt and Fe 3 O 4 was tuned by varying the synthesis parameters. The as-synthesized bimagnetic nanoparticles were superparamagnetic at room temperature. After being annealed in a reducing atmosphere, the FePt/ Fe 3 O 4 bimagnetic nanoparticles were converted to a hard magnetic nanocomposite with enhanced energy products due to the exchange coupling between the hard and soft magnetic phases. It was found that the exchange coupling in nanocomposites made from the core/shell nanoparticles is stronger than that from the heterodimer nanoparticles. By tuning the dimensions of the FePt and Fe 3 O 4 phases, the energy product up to 17.8 MGOe was achieved in the annealed nanocomposites, which is 36% higher than the isotropic single-phase FePt counterpart.

Methods have been developed for the shape-selective synthesis of ferroelectric LiNbO 3 nanoparticles. Decomposition of the single-source precursor, LiNb(O-Et) 6 , in the absence of surfactants, can reproducibly lead to either cube-or sphere-like nanoparticles. X-Ray diffraction shows that the LiNbO 3 nanoparticles are rhombohedral (R3c). Sample properties were examined by piezoresponse force microscopy (PFM) and Raman where both sets of nanoparticles exhibit ferroelectricity. The longitudinal piezoelectric coefficients, d 33 , varied with shape where the largest value was exhibited in the nanocubes (17 pm V 21 for the cubes versus 12 pm V 21 for spheres).