Jeffrey F. Godsell

Large scale monodisperse hexagonal arrays of superparamagnetic iron oxides nanodots: a facile block copolymer inclusion method.

Highly dense hexagonal ordered arrays of superparamagnetic iron oxides nanodots are fabricated by a simple and cost-effective route. Spectroscopic, microscopic and magnetic measurements show that the nanodots have uniform size, shape and their placement mimics the original self-assembled block copolymer pattern. The nanodots show good thermal stability and strong adherence to the substrate surface, making them useful for practical device applications.

Supercritical fluid synthesis of magnetic hexagonal nanoplatelets of magnetite.

A supercritical fluid technique was used to prepare hexagonal nanoplatelets of magnetite. Ferrocene was used as the Fe source, and sc-CO(2) acted as both a solvent and oxygen source in the process. Powder X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and magnetic measurements were used to characterize the products. It was found that the morphology and structure of the product strongly depended on the reaction conditions.

Block copolymer mediated stabilization of sub-5 nm superparamagnetic nickel nanoparticles in an aqueous medium

This paper presents a facile method for decreasing the size of water dispersible Ni nanoparticles from 30 to 3 nm by the incorporation of a passivating surfactant combination of pluronic triblock copolymer and oleic acid into a wet chemical reduction synthesis. A detailed study revealed that the size of the Ni nanoparticles is not only critically governed by the concentration of the triblock copolymers but also dependent on the hydrophobic nature of the micelle core formed. The synthesized Ni nanoparticles were thoroughly characterized by means of transmission electron microscopy, x-ray diffraction, x-ray photoelectron spectroscopy and temperature and field dependent magnetic measurements, along with a comprehensive Fourier transform infrared spectroscopy analysis, in order to predict a possible mechanism of formation.

Precessional dynamics of Ni45Fe55 thin films for ultrahigh frequency integrated magnetics

Future monolithic point of load switched mode power supplies will be expected to meet the energy requirements of miniaturized, high functionality electronic devices. Recently, Ni45Fe55 has emerged as a potentially important material choice for use as a soft magnetic core material within high frequency integrated passive magnetic components. The operating frequency range of the integrated passives which form a key part of the point of load power supply must increase to allow for inductor/transformer miniaturization to become monolithic with power integrated circuits. In this work, an analysis of the high frequency permeability spectra of an electroplated Ni45Fe55 thin film has been carried out to quantitatively analyze the material’s high frequency performance. Complex permeability spectra of the film have been investigated at frequencies up to 9 GHz to identify both the film’s spectroscopic splitting factor (g) and its effective dimensionless damping parameter (α). The Kittel equation is utilized to ident...

Microwave-assisted synthesis of icosahedral nickel nanocrystals

Nickel nanocrystals with icosahedral morphologies have been successfully synthesised using a microwave-assisted irradiation method. Nickel acetylacetonate was used as the metal precursor, while sodium formate and trioctylphosphine oxide were employed as the reducing agent and capping ligands, respectively. The nanocrystals, with a mean diameter of 237 ± 43 nm, exhibited enhanced ferromagnetic behaviour at room temperature compared to bulk nickel, with coercivities of up to 164 Oe and saturation magnetisation values of up to 46 emu g−1, due to their icosahedral morphologies.

Device Geometry Effects in an Integrated Power Microinductor With a Ni

In an integrated power microinductor, the size and shape of the magnetic material will have a relationship to the permeability and inductance of the device. To demonstrate these effects, a set of inductors with closed Ni45Fe55 films were fabricated having similar structures but different footprint sizes and aspect ratios (ARs). Magnetic and electrical characterization was performed on the devices to determine magnetic properties, and in both measurements the same relationship between film shape and magnetic anisotropy is observed. Micromagnetic shape anisotropy simulations were used to predict this behavior and correlate with the experimentally determined parameters. The AR of the film is determined to have a strong influence on the anisotropy and permeability of the magnetic film via shape demagnetization effects which is shown to be a significant variation from the as-deposited magnetic material parameters.

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Artificial and local control of spin-configuration in nanoscale in continuous magnetic films could enable new spin-based electronics and precision sensor technologies. Extensive theoretical research has recently been devoted to examination of surface nanovariation mediated magnetism and its utility, which has been demonstrated only in one-dimensional surface modulation. However, a realization of engineered spin configuration using two-dimensional (2D) nanomodulation is limited by local vortex formation induced by magnetostatic energy. In this work we demonstrate for the first time, an ability to control the anisotropy in continuous magnetic films by periodic surface nanomodulation in two-dimensions (2D). Magnetic properties of NiFe films with nanomodulated surfaces have been studied as a function of both film thickness and modulation amplitude. For films with a patterned square array (without breaking the film continuity), a clear fourfold symmetry of anisotropy field and coercivity was observed with rota...

Fe

Extensive research has recently been devoted to examination of surface nanovariation mediated magnetism and its utility, which has been demonstrated in one-dimensional surface modulation. In this work, we demonstrate an ability to control the anisotropy in continuous magnetic films by periodic surface modulation in two-dimensions. Magnetic properties of films with nano-modulated surfaces have been studied as a function of both film thickness and modulation amplitude. For films with a patterned square array, a clear fourfold-symmetry of anisotropy field and coercivity was observed with rotation angle. An experimental phase diagram of anisotropy with respect to film thickness and modulation amplitude has been produced. Micromagnetic simulation shows that the observed magnetic anisotropy is the consequence of minimization of magnetostatic energy.