Recent achievements in MgB2 physics and applications: A large-area SQUID magnetometer and point-contact spectroscopy measurements

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Gonnelli, R.S. and Daghero, D. and Calzolari, A. and Ummarino, G.A. and Tortello, M. and Stepanov, V.A. and Zhigadlo, N.D. and Rogacki, K. and Karpinski, J. and Portesi, C. and Monticone, E. and Mijatovic, D. and Veldhuis, D. and Brinkman, A. (2006) Recent achievements in MgB2 physics and applications: A large-area SQUID magnetometer and point-contact spectroscopy measurements. Physica C: Superconductivity, 435 (1-2). pp. 59-65. ISSN 0921-4534

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Abstract:In the first part of the present paper we discuss the fabrication and the characterization of an MgB2-based SQUID magnetometer with a directly coupled large-area pick-up loop, made on an MgB2 film deposited by an all in situ technique. The coarse structure of the SQUID was defined by optical lithography and Ar-ion milling, while the two nanobridges acting as weak links in the superconducting loop were made by focused ion beam (FIB) milling. The device was characterized at different temperatures and showed Josephson quantum interference up to 20 K as well as a noise level already compatible with the recording of an adult magnetocardiogram.

In the second part, concerning the fundamental physics of MgB2, we present the results of very recent point-contact measurements on Mg1−xMnxB2 single crystals with 34.1 Tc 13.3 K (i.e. 0.37% x 1.5%). The experimental conductance curves were fitted with the generalized two-band BTK model and their behaviour in magnetic fields was studied to check if both the order parameters (OPs) of the σ and π bands were present in the whole doping range. The dependence of the OPs (evaluated through the fit) on the Andreev critical temperature of the junctions is analyzed in the framework of the two-band Eliashberg theory by including the effects of magnetic impurities. The results give an evidence of a dominant effect of the magnetic impurities on the σ-band channel.

Item Type:Article
Copyright:© 2006 Elsevier B.V.
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Science and Technology (TNW)
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Link to this item:http://purl.utwente.nl/publications/74510
Official URL:http://dx.doi.org/10.1016/j.physc.2006.01.018
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