Marian Grigoras

Magnetotransport Phenomena in [NiFe/Cu] Magnetic Multilayered Nanowires

[Py(20-50 nm)/Cu(5-20 nm)] x n multilayered nanowires were electrodeposited by switching between the deposition potentials of the two constituents [respectively, -1.4 V and -0.3 V for permalloy (NiFe) and Cu deposition]. The magnetotransport properties of single multilayered nanowires have been measured. The MR curve is symmetrically anhysteretic, independent of the thickness of the nonmagnetic Cu layer. The MR ratio can reach values of 2%-2.5%, depending on the thickness of the nonmagnetic Cu layer. The presence of nonmagnetic Cu layers produces a decrease of the axial magnetic anisotropy in the multilayered nanowires, and consequently the magnetic permeability increases at the surface of the nanowires leading to the enhancement of the dc magnetic field effect over the MI response, which can go up to 100%.

Contact and Magnetoresistance Measurement of a Single NiFe/Cu Multilayer Nanowire Within a Template Nanowire Array

A new method for the preparation of an electrical contact on a single nanowire from an array of nanowires using focused ion beam was successfully developed. The array of NiFe/Cu multilayered nanowires was obtained by electrodeposition from a plating solution containing metallic salts. Furthermore, polyethylene glycol (PEG) was added within the deposition bath, at a controlled pH of three, to improve the magnetotransport properties of the multilayered nanowires. It was found that, at room temperature, the coercive field, Hc, of the electrodeposited multilayered nanowires decreases when the additive is added into the electrolytic bath. Magnetoresistance (MR) measurements were performed on a single nanowire from the array; the MR value increases for the nanowires with a smaller diameter and when PEG is used.

Comparative study on the uptake and bioimpact of metal nanoparticles released into environment

Metallic particles of very small size are ubiquitously released in the air, water and soil from various natural and artificial sources – the last ones with enhanced extent since nanotechnology development accelerated exponentially. In this study we focused on the impact of metal nanoparticles in vegetal species of agroindustrial interest namely the maize (Zea mais L.). Laboratory simulation of environmental pollution was carried out by using engineered nanoparticles of two types: iron oxides with magnetic properties and gold nanoparticles supplied in the form of dilutes stable suspensions in the culture medium of maize seedlings. Magnetic nanoparticle (MNPs) preparation was performed by applying chemical route from iron ferric and ferrous precursor salts in alkali reaction medium at relatively high temperature (over 80 °C). Gold nanoparticles (GNPs) synthesis was accomplished from auric hydrochloride acid in alkali reaction medium in similar temperature conditions. In both types of metallic nanoparticles citrate ions were used as coating shell with role of suspension stabilization. Plantlet response was assessed at the level of assimilatory pigment contents in green tissue of seedlings in early ontogenetic stages.

NdFeB/αFe Nanocomposite Permanent Magnets with Enhanced Properties Prepared by Spark Plasma Sintering

Nanocomposite NdFeB/αFe magnets were obtained by spark plasma sintering technique using high energy ball-milled Nd-Fe-B melt-spun ribbons mixed in different weight ratios with Fe commercial powders. The remanence of SPS nanocomposite magnets increases with the Fe powders content from 6.1 for 4 wt.% Fe to 6.4 kG for 5 wt.% Fe, while the estimated maximum energy product is also increased from 9.0 to 10.6 MGOe.

Effect of the Sputtering Power Density on Microstructure and Magnetic Properties of CoFeSiB Thin Films

The correlation between composition, microstructure, and magnetic properties of as-deposited CoFeSiB thin films has been studied by varying the sputtering power density of Co target. The CoFeSiB alloy film shows significantly different microstructure and magnetic properties depending on the Co concentration. When the Co concentration is below 72.2 at.%, the deposited thin films consist of a single amorphous phase and behave magnetically soft. Meanwhile, above 72.2 at.%, the structure consists of Co nanocrystals embedded within the amorphous matrix, and the codeposited samples show the typical antiferromagnetic exchange coupling at the interface between nanocrystals and amorphous matrix.