Magnetic Cluster Size Research Articles

The physical limits of high density recording in metallic magnetic thin film media

The fundamental physical limits of high density, saturation recording in high hysteresis loop squareness magnetic isotropic metallic media have been investigated based on observations of micromagnetic structure of recorded Co-Re thin films. Study based on the configuration of the "feather-like" ripple structures of the Lorentz TEM image at the transition region and electron deflection shadow image of the surface field configuration of the recorded media indicate that the physical limit of high density recording in the metallic media is the size of magnetic clusters existing in the film. For a Co-10 at % Re film with H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> between 200 to 500 oe., thickness of about 50 nm and S* > 90%, the maximum linear packing density the film can provide, as determined from the cluster size, would be less than 25,000 FRPI.

ChemInform Abstract: LOCAL ATOMIC ARRANGEMENTS IN A MAGNESIOWUSTITE SOLID SOLUTION

AbstractEs wird von quantitativen Untersuchungen von röntgenographischen und Magnetisierungsmessungen an (Fe,Mg)O mit 15,7% Fe berichtet, wobei die Probe bei 1400°C in reduzierender Atmosphäre gehalten wird.

Local Atomic Arrangements in a Magnesiowustite Solid Solution

Quantitative studies of diffuse X‐ray scattering and measurements of magnetization are reported for (Fe,Mg)O with 15.7 cation % Fe held in a reducing atmosphere at 1400°C and quenched. The diffuse scattering is greater for fast cooling than for slow cooling; in both cases, spinel precipitation occurs, but the amount is much larger in the latter case. From this scattering, short‐range order parameters were determined for the clustering between cations, and displacements were obtained between cations and anions. From the magnetic measurements the size of magnetic Fe ion clusters was obtained. Computer simulations of the cation arrangement with the measured short‐range order parameters indicate that the magnetic clusters cannot be accounted for by nearest‐neighbor Fe2+] clusters. However, clusters of Fe ions related by first‐ and/or second‐neighbor vectors are of the size found from the magnetic data.

Mössbauer studies of the lithium ferrite-aluminate system

Mössbauer studies of the series Li 0·5Fe 2·5− a Al a O 4 where ‘ a’ has values from 0 to 2.5 have been carried out. It is observed that in addition to the six line nuclear Zeeman spectrum, a doublet also appears at the centre and the intensity of this doublet increases with the increasing aluminium content. As a consequence of magnetic dilution, some iron species are isolated from the other magnetic species and have a short range of magnetic order. This results in varying sizes of magnetic clusters; the regions which as a whole have very little magnetic interaction with the surroundings but within which there can be any type of magnetic ordering. The relaxation rate is much faster in the smaller clusters (also referred to in literature as superparamagnetic clusters) and give rise to paramagnetic spectrum. An attempt has been made to find the relative number of iron species which give rise to paramagnetic spectrum in terms of the surrounding non-magnetic neighbours. The anomalous magnetisation behaviour of this series of compounds and the temperature dependence of the hyperfine magnetic fields at the two sites has been discussed.