Magnetic Storage Device Using Induced Magnetic Reversal of a Cobalt Element Array

The effects of the applied field, cell size, and cutting area on the ‘‘seed’’ induced magnetic reversal of a cobalt element array have been studied by a stochastic dynamic micromagnetics code using the Laudau–Lifshitz–Gilbert equation. Three magnetic reversal mechanisms under different magnitudes of the applied field have been investigated by examining the energy profiles. To minimize the effect of the thermal fluctuations on the switching time, an applied field with magnitude around 0.7 or 0.8 T and an element array with cutting area less than 10 nm X 10 nm are required. By using the smaller cellsize, the switching time and the storage density of the element array can be improved. A sinusoidal applied field with a period of 0.1 ns was used to generate a single switching event

Light Scattering Studies of Transverse Sound Wave and Molecular Motion in Benzonitrile

The zero‐frequency shear wave dip appearing in the depolarized Rayleigh spectrum in benzonitrile has been studied as a function of concentration and temperature. The solution study was carried out at constant viscosity equal to the viscosity of liquid benzonitrile at each temperature. The result indicates that the presence of shear wave fine structure does not depend on the collective orientational fluctuations. The orientational and vibrational relaxation times of benzonitrile were measured at various concentrations and temperatures. The orientational relaxation times show no concentration dependence at any temperature, suggesting that the pair correlation is negligible at all concentrations. The orientational relaxation times obtained from the Raman measurements are in good agreement with the depolarized Rayleigh values at the same temperature and concentration, again indicating pair correlation is negligible in benzonitrile. Thus, both the Raman and depolarized Rayleigh scattering techniques measure the single particle relaxation time of benzonitrile. The single particle times were compared with the predictions of the hydrodynamic slip and stick models for rotational diffusion. In contrast to the results obtained for most small molecules, the stick model better approximated the experimental results

Light Scattering Studies of Rotational and Vibrational Relaxations of Acetonitrile in Carbon Tetrachloride

The rotational and vibrational relaxation times of acetonitrile–carbon tetrachloride solutions were investigated as a function of concentration, viscosity, and temperature using depolarized Rayleigh and Raman scattering. Using a Fabry‐Perot interferometer and single frequency laser source, we have shown that reliable results for the single particle orientational correlation times (τs) for CH3CN can be obtained by carrying out a concentration dependent depolarized Rayleigh scattering study. Raman scattering was shown to yield inconsistent results for τs in CH3CN. At constant viscosity, it was found that the Rayleigh scatteringrelaxation time (τRay) of CH3CN in CCl4 does not change with CH3CN concentration, indicating that the orientational pair correlation factor of liquid CH3CN is close to unity. This result suggests that the dynamic pair correlation in CH3CN is just as important as the static pair correlation. The experimental data were also compared with the predictions of the hydrodynamic stick and slip models for a rotational diffusion. The CH3CN data were found to be close to the prediction of the slip model. The isotropic relaxation time (τiso) of the C≡N stretching mode was also studied as a function of concentration and viscosity using Raman spectroscopy. This viscosity dependence of τiso also decreases with decreasing number density of CH3CN, suggesting that pair correlations are also important in the Raman scattering of CH3CN

Monte Carlo Simulation on the Indirect Exchange Interactions of Co-doped ZnO Film

Monte Carlo simulations using a three-dimensional lattice model studied the Ruderman–Kittel–Kasuya–Yosida (RKKY) indirect exchange interaction of doped magnetic Co ions in ZnOfilms. The results of the calculations show that the RKKY interaction in Co-doped ZnO is long ranged and its magnitude is proportional to (inverse of the distance from a central ion). The sign oscillates with a frequency that depends on the concentration of the carrier. The long-distance sum of the RKKY indirect exchange energies is positive indicating that these materials are ferromagnetic, in direct correlation with previously reported results

Micromagnetics Simulation of Deep-Submicron Supermalloy Disks

The results of recent micromagnetic simulations of deep submicron supermalloy disks are presented. A recent experimental measurement of the hysteresis and magnetic domain structure in supermalloy disks with diameters ranging from 55 to 500 nm and thickness ranging from 6 to 15 nm has been reported. Our micromagnetic simulations show remarkable agreement with the experimental hysteresis loops. The simulation results show that for thin or small diameter disks a single magnetic domain exists with all spins aligned. The hysteresis loop represents free rotation of these spins. For larger diameter disks or as the thickness increases the hysteresis loops change shape due to the appearance of a single vortex state appearing at low applied fields

Micromagnetics Simulation of Nanoshaped Iron Elements: Comparison with Experiment

A micromagnetics simulation has been conducted on nanostructured magnetic elements of iron in order to investigate the effect of the shape of the element on magnetic properties, such as domain formation and hysteresis loops. These results are compared with recent experimental studies. The results display an impressive agreement with both the experimentally observed magnetic domains in individual particles as well as the shape of the hysteresis loops. The simulation results then explain features in the hysteresis loops in terms of vortice formation and motion

A Comparison of the Rough Sphere Rotational Diffusion Model with Experimental Results for Liquid Methyl Iodide

No abstract available

Thickness Dependence of Magnetic Blocking in Granular Thin Films with Interacting Magnetic Particles

Interparticle interaction among single domain nanosize magnetic particles embedded in nonmagnetic matrix was studied. Attention was paid to concentrated Cu–Co granular thin films with a fixed magnetic volume fraction (20%). By analyzing theoretical models and comparing with experimental results, a dimensional constraint on the magnetic properties was found. As the film thickness reduces toward the thin limit the interparticle interaction plays important roles in modifying the magnetic behavior. The dipolar interaction energy was calculated among magnetic particles including far-neighbor interaction for films with different thickness values. When magnetization variation is included in the calculation, the resulting calculated interaction energy versus film thickness shows remarkable agreement with the variation of experimental observed peak temperature derived from magnetic blocking curves

Thickness Dependence of Magneto-Transport in Cu-Co Granular Thin Films

This work explores the thickness dependence of magneto-transport properties in granular thin films with different thickness. These results are compared with silver-based film series studied earlier. It was observed that the thickness dependence of the GMReffect was sensitive to the surface chemistry of the films. The extraordinary Hall effect (EHE) in these films was measured and found to be different from the Ag-based system. In the Cu-based system, the EHE is a weak function of film thickness over the range studied. When the variation of the spontaneous magnetization is taken into account the effective EHE has a universal thickness dependenc