The variational-cumulant expansion (VCE) method is used to calculate the quantum XY model, for which the trial action So does not commute with the action S, with arbitrary magnitude of spin on various one-, two-and three-dimensional lattices. The free energy of the model is expanded to the third order and the analytical formulae of critical temperature T c are given for each order. To testify this method in a wider range, the Heisenberg model on different lattices is also calculated, which has more comparable results. Weighted fitting method of statistical mathematics is adopted to predict T c of infinite order.PACS numbers: 75.10.J CHEN Tianlun, WANG Qing and LIU Ruijie Vol. 28
Non-vacuum electrodeposition and spray deposition process was used to deposit Bi-2212 precursor films. Biaxially textured Bi-2212 superconductor films were prepared from electrodeposited precursor films by melt-quench/melt-growth processing on Ag-coated LAO substrates. Magnetization measurements for the electrodeposited, Bi-2212 superconductor films show critical current density values greater than 5 × 10 6 A cm −2 at 4 K in zero field. The samples were characterized by x-ray diffraction including θ /2θ , pole figures, omega scans, phi scans, resistance versus temperature (R-T ), magnetization measurements, transmission electron microscopy and scanning electron micrographs.
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