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TT: Fachverband Tiefe Temperaturen

TT 34: Superconductivity - Vortex Dynamics, Vortex Phases, Pinning

TT 34.5: Vortrag

Freitag, 30. März 2007, 11:15–11:30, H19

Pinning and disorder effects of SiC and C additions in MgB₂ by magnetic relaxation and specific heat analysis — •C Senatore¹, R Lortz¹, SX Dou², and R Flükiger¹ — ¹DPMC and MaNEP, Universite de Geneve, Switzerland — ²Institute for Superconductivity and Electronic Materials, University of Wollongong, Australia

The relatively high T_c and the reduced fabrication costs of MgB₂ render this material promising for industrial applications, especially in substitution to Nb₃Sn in the magnetic field range 9-12 T or in view of cryogen free devices, operating at 20 K. The addition of nanometric powders of SiC and C enhances both B_irr and J_c. However, the underlying physical mechanism is not completely understood. We have analyzed the effects of SiC and C doping on the superconducting properties of MgB₂ bulks by means of specific heat and magnetic relaxation measurements. Pinning in MgB₂ is governed by grain boundaries. To discriminate the influence of the additions on the pinning properties from the grain size effects, magnetic relaxation measurements have been performed on doped samples sintered at different temperatures. A series of binary MgB₂ has been used as reference. Doping introduces disorder into the superconductor and thus raises B_c2. In the case of MgB_1.9C_0.1, specific heat measurements show that the C substitution on the B sites modifies the low temperature shoulder related to the second gap. This effect is not visible in the samples doped with SiC. SiC leads to an inhomogeneous distribution of C as seen from the distribution of T_c determined from the calorimetric data.