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Dynamic magnetic properties of spins from Mn ions doped in semiconductor nanocrystals (Cd1−xMnxSe) have been studied using an electron paramagnetic resonance method based on two different crystalline sizes and a series of Mn concentrations. By decreasing the size of the quantum dots, the electron spin-nuclear spin interactions are reduced due to enhanced magnetic interactions between Mn ions. A linewidth analysis was also carried out, showing longer spin relaxation times and supporting the enhancement of spin coherence. We suggest that the enhancement of Mn–Mn interactions results from the quantized electrons which have longer coherence length in quantum dots. Quantum size effects may benefit to control and manipulation of spins in a semiconductor nanocrystalline system in which the magnetic ions are incorporated.

The application of nanoparticles as quantum dots in nanoelectronics demands their arrangement in ordered arrays. Shape controlled self-assembly is a challenge due to the difficulties of obtaining proper self-assembling parameters, such as solvent concentration, organic ligands, and nanoparticle size. In this article, hard magnetic FePt nanoparticles were synthesized using a combination approach of reduction and thermal decomposition. The nanoparticles are about 4.5 nm and appeared as truncated octahedral enclosed by the {100} and {111} crystal facets of fcc structure. The nanoparticles are of hexagonal close packing and orient randomly in the self-assembly nanoarrays. By diluting the solution for large-area self-assembly, monolayer, submonolayer, and multilayer nanorings of FePt nanoparticles were formed. The nanoring formation is determined by hydrodynamics, surface effects, and interaction between the FePt nanoparticles and substrates.

Epitaxial thin films of BiFeO3-CoFe2O4 composite were grown on spinel MgAl2O4 substrates with a (001) orientation. The composite formed an intriguing nanogrid structure where perovskite BiFeO3 forms linear mounds embedded in a matrix of spinel CoFe2O4. The structure makes a stark distinction with similar composite films on (001) perovskite SrTiO3 substrates where CoFe2O4 forms nanopillars surrounded by a BiFeO3 matrix. This result shows the interface between the film and the substrate that plays a determining role during the formation of the composite.

Magnetotransport of Fe 3 O 4 -hexabromobenzene ( C 6 Br 6 ) composite has been studied. Powders of C 6 Br 6 and Fe 2 O 3 nanoparticles were mixed together. They were annealed in hydrogen flow. There was a phase transformation from Fe 2 O 3 to Fe 3 O 4 after annealing. Giant negative magnetoresistance(MR) was observed at room temperature and the MR ratio is about 13.4% in an applied field of 5 T. The maximum MR ratio is 21.5% at 130 K. The temperature dependence of the resistivity exhibits characteristics of intergranular tunneling in the samples. The enhancement of the MR ratio is attributed to the fact that the C 6 Br 6 can act as barrier material and, more importantly, can prevent the oxidation of the surface of Fe 3 O 4 , which is believed to alter the half-metallic state at the surface.

CoFe2O4 nanoparticles prepared by chemical coprecipitation method in a magnetic field exhibit novel magnetic properties. The average particle diameter was about 2 nm and larger depending on the post annealing temperature. Magnetization measurements indicate that smaller nanoparticles are superparamagnetic above their respective blocking temperatures. In the blocked state, these nanoparticles exhibit interesting behaviors in the magnetic hysteresis measurements. Constricted, or wasp waisted with extremely narrow waist, hysteresis curves have been observed in the magnetization versus field sweeps. For larger nanoparticles, the room temperature hysteresis is typical of a ferromagnet with an open loop, but the loop closes at lower temperature. The novel magnetic behavior is attributed to the directional order of Co ions and vacancies in CoFe2O4 established during the coprecipitation of the nanoparticles under an applied field.

We have prepared nanometer-sized CoPt particles dispersed in a poly(methyl methacrylate) (PMMA) matrix, as a novel nanostructured magnetic plastic, through a soft chemical processing route. In this work, CoPt nanoparticles were successfully synthesized from a solution phase reduction system in the presence of capping ligands and stabilizing agents at high temperature. The CoPt nanoparticles were annealed at 400 °C for 3 h, and were subsequently re-dispersed in methylmethacrylate (monomer). The polymerization was induced by a UV source and the hardness of final product was adjusted by varying the amount of monomeric cross-link agent. Annealed bare CoPt nanoparticles as a “core” material and CoPt–PMMA composite material were characterized by using energy dispersive spectroscopy, transmission electron microscopy, and x-ray diffraction, indicating that we are able to prepare CoPt nanoparticles with

A series of (Co50Fe50)x-(Al2O3)1−x cermet granular thin films deposited on glass substrates by dual electron beam evaporation was studied for their structural, magnetotransport, and magnetic properties. Upon varying the magnetic volume fraction, x, from 0.07 to 0.52 the percolation threshold (xc) was determined from resistivity measurements to be ∼0.17. This value agrees well with the theoretical prediction for a three-dimensional system of spherical particles. Values of the isotropic tunneling magnetoresistance (TMR) as high as 10% at room temperature were found for films with x