12 research outputs found
Synthesis and Bulk Properties of Oxychloride Superconductor Ca2-xNaxCuO2Cl2
Polycrystalline samples and submillimeter size single crystals of Na-doped
Ca2CuO2Cl2 have been synthesized under high pressure. A series of experiments
showed that the Na content depends not only on the pressure during the
synthesis but also on the synthesis temperature and time. From a comparison of
the Na-CCOC data with those of structurally related La214 cuprate
superconductors we concluded that chlorine at the apical site is less effective
that oxygen in supplying charge carriers to the CuO2 plans. As a result, the
coupling between the CuO2 planes is weakened, the transition temperature Tc is
reduced and the anisotropic nature is enhanced.Comment: 7 pages, 7 figures, 1 table, presenthed at the Eucas 2007 conference.
Accepted for "Journal of Physics: Conference Series (JPCS)" 2008 and European
News Forum, Issue 3 (2008
Strong magnetic pair breaking in Mn substituted MgB_2 single crystals
Magnetic ions (Mn) were substituted in MgB_2 single crystals resulting in a
strong pair-breaking effect. The superconducting transition temperature, T_c,
in Mg_{1-x}Mn_xB_2 has been found to be rapidly suppressed at an initial rate
of 10 K/%Mn, leading to a complete suppression of superconductivity at about 2%
Mn substitution. This reflects the strong coupling between the conduction
electrons and the 3d local moments, predominantly of magnetic character, since
the nonmagnetic ion substitutions, e.g. with Al or C, suppress T_c much less
effectively (e.g. 0.5 K/%Al). The magnitude of the magnetic moment, derived
from normal state susceptibility measurements, uniquely identifies the Mn ions
to be divalent, and to be in the low-spin state (S = 1/2). This has been found
also in X-ray absorption spectroscopy measurements. Isovalent Mn^{2+}
substitution for Mg^{2+} mainly affects superconductivity through spin-flip
scattering reducing T_c rapidly and lowering the upper critical field
anisotropy H_{c2}^{ab}/H_{c2}^c at T = 0 from 6 to 3.3 (x = 0.88% Mn), while
leaving the initial slope dH_{c2}/dT near T_c unchanged for both field
orientations.Comment: 9 pages, 9 figure