https://www.andrew.cmu.edu/user/dl0p/laughlin/pdf/PMS.pdf

Amorphous and nanocrystalline materials for applications as soft magnets

In this review paper, the state-of-the-art knowledge of the core–shell multifunctional nanoparticles (MNPs), especially with unique physiochemical properties, is presented. The synthesis methods were summarized from the aspects of both the advantages and the demerits. The core includes the inexpensive and easily oxidized metals and the noble shells include the relatively noble metals, carbon, silica, other oxides, and polymers. The properties including magnetic, optical, anti-corrosion and the surface chemistry of the NPs are thoroughly reviewed. The current status of the applications is reviewed with the detailed examples including the catalysis, giant magnetoresistance (GMR) sensing, electromagnetic interface shielding or microwave absorption, biomedical drug delivery, and the environmental remediation.

Multifunctional composite core–shell nanoparticles

Colloidal assemblies are used to synthesize FCC cobalt nanoparticles. The particles are coated, extracted from micelles, and characterized by transmission electron microscopy, small angle X-ray scattering, and electron and X-ray diffraction spectroscopy. These cobalt metal particles are stable in air, have a narrow size distribution, and on deposition on a graphite support, spontaneously form a 2D hexagonal network. The magnetic properties are compared when they are dispersed in a solvent and organized in 2D superlattices. Changes in the hysteresis loop and in the blocking temperature are observed and attributed to collective flip of the magnetization of adjacent particles.

Cobalt nanosized particles organized in a 2d superlattice : synthesis, characterization, and magnetic properties

Sodium borohydride reduction of silver ions in aqueous dispersions of exfoliated graphite oxide (GO) resulted in the formation of remarkably monodisperse 100 A diameter oblate Ag particles that are effectively protected by 5 A thick GO sheets, Ag−GO. Ag−GO could be self-assembled onto poly(diallyldimethylammonium) chloride, PDDA, coated substrate; subsequent layer-by-layer self-assembly of Ag−GO and PDDA led to well-ordered ultrathin films of S-(PDDA/Ag−GO)n.

Preparation and Layer-by-Layer Self-Assembly of Silver Nanoparticles Capped by Graphite Oxide Nanosheets

The synthesis of carbon coated Fe, Co and Ni nanoparticles and an examination of their magnetic properties

We report the structure and magnetic studies of carbon coated nanocrystals of nickel and cobalt synthesized in a special low carbon to metal ratio arc chamber. Powder x-ray diffraction profiles show peaks associated with single phase of fcc nickel or cobalt and major peaks of graphite with no evidence of carbides or solid solutions of carbon in the metal. Measured lattice spacing of crystalline particles and that of graphite coating from high-resolution transmission electron microscope images also confirm such findings. Magnetization measurements as a function of temperature in the range 20–900 °C give a Curie temperature equal to that of bulk metal within the experimental error. Upon heating and recooling of the particles a larger magnetization as high as 57% of bulk Co and 53% of bulk Ni was measured. Also M–H hysteresis loop of the particles have been measured at room temperature after annealing in the temperature range 20–650 °C for Ni, and 20–900 °C for Co. The dependence of room temperature saturation magnetization, remanent magnetization, and coercive field of the particles on annealing temperature is reported. These data are described by transition of particles form single domain to multidomain as a result of particle growth due to annealing. We also present the particle size distribution measurements that show log-normal behavior, and indicate substantial particle size growth due to annealing.

R. LaDuca

Papers

Effect of annealing on the structure and magnetic properties of graphite encapsulated nickel and cobalt nanocrystals