Monica Moldovan

Magnetic and electromagnetic evaluation of the magnetic nanoparticle filled polyurethane nanocomposites

The magnetic and electromagnetic wave absorption behavior of a flexible iron-nanoparticle reinforced polyurethane nanocomposite is reported. Surface-initiated-polymerization (SIP) method was utilized to fabricate high-quality nanocomposites with uniform particle distribution and tunable particle loading (up to 65wt%). The enhancement of coercive force is observed when the nanoparticles are embedded into the polymer matrix. Electromagnetic wave absorption performance at a discrete frequency as studied by metal-backed reflection loss indicates that the SIP nanocomposites can save the weight up to 50% compared to the composite counterpart with micron-size particles.

Giant magnetoresistance behavior of an iron/carbonized polyurethane nanocomposite

This letter describes the magnetoresistance (MR) behavior of the heat treated polyurethane composites reinforced with iron nanoparticles. The flexible nanocomposites were fabricated by the surface-initiated-polymerization method. The uniformly distributed nanoparticles within the polymer matrix, well characterized by field emission scanning electron microscopy, favor a continuous carbon matrix formation, rendering the transition from insulating to conductive composites. The coercive forces reflect strong particle loading and matrix dependent magnetic properties. By simply annealing in a reducing environment, the obtained nanocomposites possess a MR of 7.3% at room temperature and 14% at 130K occurring at a field of 90kOe.

Flexible high-loading particle-reinforced polyurethane magnetic nanocomposite fabrication through particle-surface-initiated polymerization

Flexible high-loading nanoparticle-reinforced polyurethane magnetic nanocomposites fabricated by the surface-initiated polymerization (SIP) method are reported. Extensive field emission scanning electron microscopic (SEM) and atomic force microscopic (AFM) observations revealed a uniform particle distribution within the polymer matrix. X-ray photoelectron spectrometry (XPS) and differential thermal analysis (DTA) revealed a strong chemical bonding between the nanoparticles and the polymer matrix. The elongation of the SIP nanocomposite under tensile test was about four times greater than that of the composite fabricated by a conventional direct mixing fabrication method. The nanocomposite shows particle-loading-dependent magnetic properties, with an increase of coercive force after the magnetic nanoparticles were embedded into the polymer matrix, arising from the increased interparticle distance and the introduced polymer?particle interactions.

Magnetoresistance and Annealing Behaviors of Particulate Co–Au Nanocomposites

Co core Au shell nanoparticles, stabilized with a sulfobetaine surfactant, were fabricated from a displacement reaction of Au 3+ with Co nanoparticles and compressed into a granular composite. The affect of annealing the composite in a hydrogen environment was investigated and found to have a dramatic effect on the magnetic properties, size, and composition of the CoAu nanoparticles. A negative magnetoresistance was observed and exhibited a parabolic functionality with annealing temperature, increasing and then decreasing with annealing temperature. A similar behavior was observed for the coercivity, attributed to the increase in particle size with the annealing temperature. The surfactant was decomposed with annealing.

Synthesis, structure, and magnetism of a new heavy-fermion antiferromagnet, CePdGa6

Abstract A new compound, CePdGa 6 , and its isostructural analog, LaPdGa 6 have been synthesized by flux growth and characterized by single-crystal X-ray diffraction. The compounds adopt a tetragonal structure with P 4/ mmm space group, Z =1. The lattice parameters for CePdGa 6 are a=b=4.350(3) A and c=7.922(6) A and a=b=4.3760(3) A and c=7.9230(5) A for LaPdGa 6 . Magnetic and thermal measurement have revealed that CePdGa 6 is a heavy-fermion with the specific heat coefficient γ∼300 mJ / mol K 2 and Ce f moments order antiferromagnetically along c -axis at T N =10 K . Reconfiguration of spin occurs at 5 K to induce a ferromagnetic component only in the a–b plane. This strong anisotropy in the magnetism might be related to its unique layered structure.

Magnetoresistance in Electrodeposited CoNiFe ∕ Cu Multilayered Nanotubes

Multilayered CoNiFe/Cu nanotubes were electrodeposited in nanoporous membranes under pulsed potential conditions from a single electrolyte. Giant magnetoresistance (GMR) measured with the current applied perpendicular to the plane of the layers was obtained at room temperature. This is the first demonstration of GMR in a nanotubular structure. We observed the value of the GMR at room temperature to be sensitive to the alloy layer deposition potential.

Electrochemical Inspection of Electrodeposited Giant Magnetoresistance CoNiCu ∕ Cu Multilayer Films

Electrodeposited multilayers, having different magnetic layer compositions, have been deposited with galvanostatic pulses onto rotating disk electrodes. Giant magnetoresistance (GMR) of 11% was observed for electrodeposited CoNiCu multilayers containing 2000 bilayers of a CoNiCu alloy and Cu spacer layer. The multilayers deposited under the same deposition conditions, or with the same layer thickness, from an electrolyte without Ni, resulted in lower values. Therefore, inspection of the cathodic and anodic partial current densities in different Ni-containing electrolytes was investigated. Factors that contributed to larger GMR values were (i) a change in the Cu deposition potential to a more cathodic region and (ii) an improvement of the magnetic sublayer corrosion resistance.

Electrodeposited, GMR CoNiFeCu Nanowires and Nanotubes from Electrolytes Maintained at Different Temperatures

Nanowires and nanotubes with modulated composition to realize a magnetoresistance effect were potentiostatically electrodeposited into alumina nanoporous templates. The multilayers were modulated between a Co-rich alloy and a Cu layer. The structure was characterized by electron microscopy. Deposits obtained from room temperature and 50°C electrolytes were nanowires, and a giant magnetoresistance (GMR) of up to 20% was observed. Chilling the electrolyte to 4°C resulted in nanotubes with a modulated structure. The current-potential behavior was examined with voltammetry and pulse transients. As expected, the cathodic current density increases with electrolyte temperature, although less obvious is the unfavorable anodic component, resulting during the transition between depositing the magnetic layer and a copper layer, which changes with time and differs with variable electrolyte temperature.

Electrolyte Effect on Nanotubes Properties

The ability to electrodeposit magnetic (CoNiFeCu) and semiconductor (Bi2Te3) nanotubes was demonstrated from two different electrochemical systems. Electrodeposited multilayered CoNiFeCu/Cu nanotubes were fabricated by pulsing the applied potential. The electrolyte temperature affected the tube formation and the nanotubes giant magnetoresistance (GMR) saturation field. Both p/n-type Bi2Te3 alloy nanotubes were deposited under constant potential from different electrolyte concentrations and component ratios. We report the Seebeck coefficient measurement method for Bi2Te3 alloy nanotubes obtained by electrodeposition.

An investigation on granular-nanocomposite-based giant magnetoresistance (GMR) sensor fabrication

The magnetoresistance behavior of the polyurethane composites reinforced with iron nanoparticles which has been heat treated was reported. The flexible nanocomposites were fabricated by the surface-initiated-polymerization (SIP) method. The uniformly distributed nanoparticles within the polymer matrix, well characterized by field emission scanning electron microscopy, favor a continuous carbon matrix formation after annealing, rendering the transition from insulating to conductive composites. The coercive forces reflect strong particle loading and matrix dependent magnetic properties. The obtained nanocomposites possess fairly good giant magnetoresistance (MR), with a MR of 7.3 % at room temperature and 14 % at 130 K. Furthermore, the formed carbon matrix has a 7 wt.% argon adsorption potential for fuel cell applications.