SUPERCONDUCTING PROPERTIES OF SN ADDED (BIPB)2SR2CA1CU2OY

The addition of Sn in two layered bismuthate superconductors has been investigated using EDAX and SEM. The addition of Sn was found to enhance T(c) from 88 K(Sn= 0) to 95 K (Sn = 0.3). The possible increase in oxygen content may be the reason for the increase in T(c)

XPS Studies of Single Crystals of Bi-2212, Tl-2212 and Tl-2223

High quality single crystals of Bi-2212, Tl-2212 and Tl-2223 were studied using X-ray photoelectron spectroscopy. From a deconvolution of the Cu2p3/2 main line, we have shown that the density of O 2p holes in the Cu-O planes are qualitatively similar in case of the Bi and Tl-2212 systems even though they have shown many other differences in their electronic structure properties. Also the results show a dependence of the density of holes on the number of Cu-O planes as we go from Tl-2212 to Tl-2223

Role of Out-of-Plane Copper and Thallium Orbitals in Thallium Cuprate

Simultaneous total and fluorescence yield XAS measurements on Cu L3-edge and, for the first time, total yield measurements at Tl L3-edge of well oriented Tl(2212) thin films are reported in this work. Also, Cu L3 and O K-edge measurements on overdoped Tl(2212) thin films using bulk sensitive fluorescence yield detection mode are reported showing that large out-of-plane hole densities do exist in the thallium cuprates at least for overdoped samples. Our results suggest that use of a bulk sensitive technique is necessary in order to get a reliable estimation of states having Cu 3dz2r2 character and thus a precise knowledge of sample stoichiometry. No direct correlation is found between Tc and out-of-plane covalent and doping hole densities such that theories based on the existence of large fraction of these out-of-plane unoccupied states are ruled out. To understand the role of out-of-plane copper orbitals, polarization dependent measurements of Cu L3-absorption edge on well characterised Tl(2212) thin films have been performed. The density of unoccupied states having 3dz2-r2 character is found to depend on the amount of doping suggesting that out-of-plane copper orbitals essentially play a role of hole reservoir. The energy shift in the positions of white lines of E//(a,b) and E//c spectra is also found to be doping dependent. The probable reason for the observed shift is discussed

High-temperature ferromagnetism in pulsed-laser deposited epitaxial (Zn,Mn)O thin films: Effects of substrate temperature

We report on the observation of remarkable room-temperature ferromagnetism in epitaxial (Zn,Mn)O films grown by a pulsed-laser deposition technique using high-density targets. The optimum growth conditions were demonstrated from x-ray measurements, microstructure, Rutherford backscattering, micro-Raman, and magnetic studies. Superior ferromagnetic properties were observed in (Zn,Mn)O films grown at a substrate temperature of 500 °C and with an oxygen partial pressure of 1 mTorr. Ferromagnetism becomes weaker with increasing substrate temperature due to the formation of isolated Mn clusters irrespective of higher crystalline quality of the film

Polarized x-ray absorption spectroscopy of unoccupied electronic states near the Fermi level in the Bi2Sr2CaCu2O8+x system

A study of the electronic states near the Fermi level in high-T-c superconductors, which is so important to understanding the mechanism of superconductivity, has been carried out on well characterized single crystals of superconducting Bi2Sr2CaCu2O8+x Bi-2212. A large number of polarized x-ray absorption spectra have been recorded with the E vector parallel to the a-6 plane and perpendicular to it at the Dragon beam line at the Brookhaven Light Source using the fluorescence mode of detection. These bulk spectra of Cu L(3) and O K are then analysed to obtain the density of the unoccupied Cu 3d(z2) and Cu 3d(x2-y2) orbitals from the Cu L(3) spectra and the density of the O 2p(z) and O 2(x,y) orbitals from the O K spectra. The results clearly show the presence of O 2p(z) orbitals in a substantial amount although the same cannot be said of the 3d(z2) orbitals. Tight-binding calculations of the holes are also reported and compared with experimental results

Ferromagnetic properties of epitaxial manganite films on SrTiO\u3csub\u3e3\u3c/sub\u3e/Si heterostructures

We report on the magnetic properties of epitaxial La0.7Ba0.3MnO3 and La0.7Sr0.3MnO3 films on Si (100) and Si (111) substrates using SrTiO3 template layer, which demonstrate magnetic and electrical properties at and above room temperature. The magnetization data show magnetic transition and magnetic hysteresis at and above room temperature. The films show well-defined magnetic domains. The ferromagnetic resonance studies show anisotropic effects related to ferromagnetic properties of films. The smaller grain size of about 20 nm in manganite films on SrTiO3 /Si may be one of the reasons to minimize the strain effect through strain relaxation at the interface between SrTiO3and manganites through the formation of three-dimensional islands