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A serial of [Pt/Co]4/MgO/[Co/Pt]2multilayers were prepared by magnetron sputtering in this study and Antiferromagnetic (AF) interlayer coupling was observed with increasing MgO spacer thickness. Perpendicular magnetic anisotropy of soft layer in [Pt/Co]4/MgO/[Co/Pt]2multilayers were measured by Extraordinary Hall Effect (EHE). The direction of the magnetic field was parallel to the direction of the current. The results revealed that perpendicular magnetic anisotropy constant Kuoscillates with the thickness of MgO layer which is between 1.3 to 3.3 nm. The period of this oscillation is about 0.43 nm. This is very close to the monolayer (100) MgO. With increasing MgO spacer, the periodic variation of interface between [Pt/Co]nand MgO layer may be one of the reasons for this oscillation behavior of Ku.

We have studied the effect of an external electric field on the dc fractional quantum Hall conductivity of a two-dimensional system with the dynamic structure function in the single-mode approximation. In analogy with the integral quantum Hill effect and superconductivity, a gap-dependent critical electric current J e also exists in the case of fracctional quantum Hall conduction, above which is the maximum current for system to maintain superfluidity. We also find that, depending on the gap width and the phonon velocity, phonon may or may not contribute to the conductivity even at a finite lattice temperature, in agreement with experiments.

Balance equations are established for steady-state nonlinear electronic transport in the presence of an electric field both for a single quasi 1D-heterostructure and for a multi–quantum–wire superlattice. The carrier-impurity scatterings and carrier–phonon scatterings have been taken into account. The general equations for determining the resistivities are obtained and the Ohmic mobility formula are given. The density-density correlation functions for the wire structures are also studied in some detail.