Tim Mercer

Fabrication of novel hierarchically ordered porous magnetic nanocomposites for bio-catalysis

Novel hierarchically ordered porous magnetic nanocomposites with interconnecting macroporous windows and meso-microporous walls containing well dispersed magnetic nanoparticles have been fabricated and used as a support to immobilise lipase for the efficient hydrolysis of ester.

Remanent state noise measurements on magnetic recording media

Abstract Media noise has been investigated as a function of both the isothermal remanent magnetisation (IRM) and DC-demagnetisation (DCD) processes on a modified audio transport. Captured noise time series from a given remanent state has been analysed for spectral content using signal processing software. These noise spectra display changes in magnetic microstructure of the tested media with remanent state. Measurements have been made on a range of commercial and laboratory produced tapes. The paper concentrates on examples of commercial samples which have been chosen to indicate various noise characteristics. Conventional media usually show similar features, but changes in remanent state noise has been observed in tapes for new formats and in recent manufacture of conventional formats. This indicates changes in magnetic microstructure associated with new particles and dispersion techniques.

The fabrication and characterization of stable core-shell superparamagnetic nanocomposites for potential application in drug delivery

Two systems of core-shell superparamagnetic nanoparticles in the size range of 45–80 nm have been fabricated by the coating of bare magnetite particles with either mesoporous silica or liposomes and the loading/release of the anti-cancer drug Mitomycin C (MMC) from their surfaces has been investigated. The magnetic cores of size ∼10 nm were produced by a co-precipitation method in aqueous solution, with the silica coating containing an unstructured network of pores of size around 6 nm carried out using a surfactant-templating approach and the liposome coating achieved by an evaporation-immersion technique of the particles in a lipid solution. Stability measurements using a scanning column magnetometry technique indicated that the lipid-coating of the particles halts the sedimentation otherwise apparent in <1 h for the bare magnetite to produce an ultra-stable system and thereby overcome one of the main barriers to potential in-vivo applications. Whilst an increase in stability was also observed in the sil...

EFFECTS OF MAGNETIC INTERACTIONS ON THE STABILITY OF PARTICULATE DISPERSIONS

The effects of magnetic interactions on the stability of recording media dispersions has been investigated. Variation of the pigment’s magnetic content shows that increasing the interactions results in lower stability. This has been interpreted in terms of hindered settling theory as being caused by clustering of the particles in suspension under the influence of magnetostatic attraction. As dispersion structure is important in the media manufacturing process, these investigations are continuing.

The Observed Linearity and Detection Response of Magnetic Fluid Concentration Magnetometry—A Theoretical and Experimental Description

The response of a scanning column magnetometer (SCM) used to measure concentration profiles of columns of magnetic dispersions has been investigated experimentally and theoretically. From the observed linearity of the total SCM output signal as a function of magnetic particle concentration, a consistent theoretical description is developed that assumes a small sensing coil field and no on-going particle agglomeration. Further theoretical development resulted in a detection coil response function that compared well with the measured response of a delta function approximation in the form of a thin ferrite disk and means that the SCM response function and spatial resolution may be determined from the coil design alone.

DC modulation noise in clustered particulate media

Mallinsons theory of recording media noise is extended to ensembles where the particles have an easy axis distribution or are clustered. The effect of clusters is that there is a critical value of packing fraction at which noise in the demagnetised state switches to a minimum. Comparison is made with measurements of DC modulation noise in double layer MP tape.

Hindered settling of particulate dispersions

A computer simulation has been developed that models hindered settling in particulate recording media dispersions. The resulting effective pigment concentration profiles compare well with experimental observations carried out using a scanning column magnetometry technique. Rigorous testing for mass conservation gives added confidence in the feasibility of this model as an aid in the study of suspension structure. As this structure is important in the media manufacturing processes of coating, orientation and drying, these investigations offer the potential to enhance the qualities of the final product.

Dispersion stability during the settling process

A technique is described which uses a scanning column magnetometer to obtain a magnetic profile of a column of dispersion of magnetic recording particles. By comparing profiles as a function of time, settling of particles can be observed. Analysed data for different dispersions can provide a comparison of their stability. The technique has the potential to combine data with rheological properties and, using hindered settling theory, to analyse the structure of magnetic particle clusters in the dispersion. This will assist in understanding tape-production processes such as orientation, surface conditioning and drying.

Effects of magnetic layer thickness and of head-to-medium spacing on noise in advanced particulate recording media

The effects of magnetic layer thickness on the noise characteristics of advanced metal particle tape have been observed using a dc demagnetization process generated with a uniform in-plane magnetizer. The three-dimensional (3D) surface maps of spectral noise power plotted as a function of remanent magnetization state showed a change in behavior as the recording layer became thinner. The thickest magnetic coating of 310 nm showed “trough-like” characteristics associated with conventional thick particulate media. The thinnest sample with a 165 nm magnetic coating showed a “peak-like” response that is observed in continuous thin-film media, with a graduated trend from one to the other for the two intermediate samples. A simulation of these results has been made with an 8000 spherical particle micromagnetic model of the media remanent states and a simulated magnetoresistive read head. Noise maps produced from the simulation compared well with experiment. Spatial isolation of the noise contributions was achiev...

Effects of magnetic layer thickness on noise in advanced double-layer metal particle tape

A series of advanced metal particle tapes with identical particles but different magnetic coating thicknesses from 300 to 150 nm have been taken through a dc-demagnetization remanent process from positive to negative saturation. Magnetization was achieved with an electromagnetic device, which produced uniform magnetization in the longitudinal direction of the tape. Spectral noise power maps have been generated for the tapes following these demagnetization processes. The thickest tape showed characteristics similar to those of conventional thick tapes, such as video, with demagnetized noise lower than the saturation noise, whereas the thinnest was characteristic of a thin film with demagnetized noise greater than that at saturation. A representation of the experimental measurement process, based on a Landau–Lifshitz–Gilbert model of the medium and a simulation of the “reading” process, generated many of the experimental features. The changes in the noise maps with magnetic coating thickness were attributed...