MAGNETIC POLARIZATION OF SPACER Pd LAYER AND MAGNETIC PROPERTIES OF Co/Pd MULTILAYERS

Magnetic multilayers［Co(1.5 nm)/Pd(x nm)］₄₀ grown by rf sputtering were studied by X-ray diffraction,vibrating sample magnetometer,torque magnetomet er and magnetoresistance measurements.The dependences of the interfacial roughne ss and the structure perfectness of Co/Pd multilayers on the spacer Pd layer thi ckness have been revealed from X-ray diffraction data.An oscillatory variation of saturation magnetization versus the thickness of the Pd spacer was observed.A similar oscillatory behavior in the dependence of its magnetic anisotropy on the thickness of the Pd spacer was observed.It is suggested from these two phenomen a that the magnetic polarization of Pd spacers oscillates between ferromagnetic and antiferromagnetic polarization with the increase of Pd spacer thickness under a RKKY-like interaction.Evidence is found for the antiferromagnetic polarization of the inner part of the Pd spacer.The antiferromagnetic coupling between two Co layers and giant magnetoresistance effect in Co/Pd multilayer system were not observed.The relationship among structure,interlayer coupling and magnetic polarization effect of the Pd spacer was discussed.     

THE AVAILABILITY OF SOLAR RADIATION BELOW 290 nm AND ITS IMPORTANCE IN PHOTOMODIFICATION OF POLYMERS

Abstract— On a percentage basis, ozone is a very minor component of the atmosphere; at STP it would make a layer only about 2 mm thick. On almost every other basis (biological, meteorological, paleontological, photochemical, etc.) it is a major component, due mainly to the tremendous reduction in solar ultraviolet flux which it causes in the 220–290 nm region. Since no data are available for Λ < 285 nm, a rational basis for estimating the flux reaching the earth's surface in this region is discussed. Variations in ozone concentration are of great importance, and it is possible to have more radiation with Λ < 270 nm fall on a surface in one extreme day than in several years of typical days. Often, persons involved in studies of polymer degradation by sunlight mention that a negligible fraction (1 ppm) of the radiant flux reaching the earth's surface is associated with wavelengths below 290 nm and infer that studies at shorter wavelengths will not be of much practical value. Such inferences are questionable for at least two reasons. (1) The quantum flux density below 290 nm is about 10¹⁶ photons cm^-2 month^-1, so that considerable long-term damage is possible since most of the flux will be absorbed in a layer only a few microns thick. (2) Even if solar radiation below 290 nm were completely absent, the existence of correlations between absorption peaks in the near ultraviolet and visible, and in the infrared with ionization potentials typically 6–12 eV or 200-100 nm) is evidence that we may expect studies in the ultraviolet and extreme ultraviolet (EUV) to provide important clues to the problem of improving the resistance of polymers to sunlight.     

Modelling avalanche flows

We present a lattice model that illustrates avalanche flow ina driven, disordered system. Structural disorder is associatedwith rectangular grains that have orientational degrees of freedom.Grain orientation transitions couple the evolving disorder withsurface instabilities. The simulated event size distributionhas features in common with observed surface granular flow and,in contrast to previous sandpile models, does not have a simplescaling behaviour. We have identified properties of the sandpilesurface that correlate with the internal structural disorder.The simulation results support a model of granular dynamicsin which surface flow and granular relaxation processes arestrongly coupled.     

The Ornstein-Zernike equation for a fluid in contact with a surface

(Molecular Physics, 1976, 31, 1291)     

PRODUCTS AND RELATIVE REACTION RATES OF THE OXIDATION OF TOCOPHEROLS WITH SINGLET MOLECULAR OXYGEN

Abstract— The relative reactivity of singlet molecular oxygen, 0₂(¹Δ_g), α-,β-,Γ-and δ with -tocopherol (vitamin E) was investigated using microwave discharge generation as a uniquely clean source of singlet oxygen and using a hydrocarbon solvent to approximate the membrane environment. The relative efficiencies of the tocopherols for O₂(¹Δg) were found to decrease in the order: D-α-tocopherol > D-β-tocopheroI > D–Γ-tocopherol > D-δ-tocopherol. The reaction products in all cases were found to be mixtures of quinone and quinone epoxides apparently resulting from decomposition of the primary product, the hydroperoxydienone.     

Molecular dynamics study of electron gas models for liquid water

The frozen density electron gas model proposed by Gordon and Kim for rare gas systems has been implemented in a molecular dynamics code. This code has been applied to investigate various options for extending this scheme to inter-molecular interactions in liquid water. We have compared a number of gradient corrections to the Thomas-Fermi kinetic energy. We also explored a more empirical approach based on adaptation of the frozen molecular electron density to the condensed phase environment. Consistent with experience from force field methods, enhancement of the molecular dipole moment proved to be necessary to reproduce the properties of the liquid. The best models we investigated are a gradient corrected expansion of the simple local density Hamiltonian applied in the original Gordon and Kim model. In addition, these models observed a modified molecular electron density carrying the same dipole moment of 2.95 D as has been observed by recent ab initio molecular dynamics studies based on fully self-consistent Kohn-Sham methods. Possible implications of this finding for force field models are discussed.     

Magnetic fields in the spiral arms of galaxies

Ordered magnetic fields observed in the Galaxy are approximately aligned along the axis of the spiral arms. The magnetic field strength is 3 microgauss but the total energy of the galactic magnetic field is as high as 1055ergs. The magnetic field direction is observed to reverse between adjacent spiral arms and this configuration requires an electric current sheet to loop each arm. Mechanisms for creating an electric current are discussed and attention is focused on the possibility of a net proton current. This requirement may be compatible with the indications that partially ionized gas is rolling round the spiral arms as they orbit the Galaxy. There is evidence which suggests that the direction of roll of the gas also reverses between adjacent spiral arms. There is a well known coincidence between the energy density of the galactic magnetic field and the energy density of turbulent gas motions, both are close to 1eVcm–3. Possible origins for these energies and the implications of this coincidence are discussed.     

ChemInform Abstract: Synthesis and Structure of Two New Layered Ternary Nitrides,SrZrN2 and SrHfN2.

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