Experimental Investigations of HTSC

The complexity of HTSC structures and properties has resulted in a small number of directed observations and test dependencies of the type “structure–property.” By this, nuclear magnetic resonance (NMR) and electron-spin resonance (ESR) are powerful exper

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Experimental Investigations of HTSC

4.1 Experimental Methods of HTSC Investigations 4.1.1 Special Techniques The complexity of HTSC structures and properties has resulted in a small number of directed observations and test dependencies of the type ‘‘structure–property.’’ By this, nuclear magnetic resonance (NMR) and electron-spin resonance (ESR) are powerful experimental methods for investigation of condensed matter. The used techniques demand a doping superconductive cuprates by using small concentrations of Gd- or Mn-ions. The arising ESR-signal provides with information on electron spins of CuO2-planes. Majority atoms in superconductive cuprates have isotopes which can lead to NMR-signals, namely: 89Y, 135Ba, 137Ba, 63Cu, 65 Cu, 17O, 139La, 207Pb, 203Tl, 205Tl, 209Bi, 151Eu, 153Eu. To regret, the abundant 16 O-isotope has not nuclear moment, therefore the oxygen studies require an enrichment of test specimen by 17O-isotopes. NMR-nuclei are sensitive not only to magnetic effects, but if their spins are greater than ‘, then electric and charge effects. As a result, NMR can differ the signals of definite nuclear isotope which presences in more than one crystalline cell. For example, NMR in YBCO can study atoms of Cu (or O) into CuO-planes separately of the atoms of Cu (or O) in corresponding links, and it can state a difference between oxygen atoms disposing into the same plane and forming Cu–O links in parallel and perpendicular directions of the links. Moreover, NMR can study both as static as dynamic effects in dependence on temperature and value of magnetic field. While NMR is a point probe, it can also state in some cases a dependence of wave vector. The studies of NMR intensity have discovered in some cases probable arising state of spin glass in HTSC at decreasing temperature [1584]. Among methods of three-dimensional observation the magnetic vortex structures in HTSC, the small angle neutron scattering and spin precession of polarized muons have an important application as the means of microscopic research of the local magnetic fields, but the Bitter decoration method is treated as the most often

I. A. Parinov, Microstructure and Properties of High-Temperature Superconductors, DOI: 10.1007/978-3-642-34441-1_4,  Springer-Verlag Berlin Heidelberg 2012

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4 Experimental Investigations of HTSC

used method of spatial resolution [172]. By using the neutron scattering method, it has been obtained direct proof for formation of wave of the spin (charge) density at the T \ T*, where T* is the temperature of the pseudo-gap arising. The Bitter decoration method utilizes small ferromagnetic particles for decorating the magnetic domain structure. When these particles are sprinkled on a material, displaying at its surface an inhomogeneous distribution of magnetic flux density, the particles are attracted to the regions with the largest value of the local magnetic field. This method has demonstrated high effectiveness in visualization of the vortex structures localized at defects [381, 1752]. The great achieve

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