Preparation and characterization of superconducting MgB₂ films on alumina

Authors: Kühberger M.; Gritzner G.; Schöppl K.R.; Weber H.W.; Olsen Å.A.F.; Johansen T.H.

Source: Superconductor Science and Technology, Volume 17, Number 6, June 2004 , pp. 764-769(6)

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Abstract:

Polycrystalline MgB₂ films with a thickness of about 1 µm were prepared at ambient pressure. The boron layers were deposited onto single-crystalline and polycrystalline Al₂O₃ by screen printing, by airbrush techniques or by painting, followed by a reaction with Mg vapour. Grinding, mechanical and electrolytic polishing in non-aqueous dimethyl sulfoxide significantly improved the surface smoothness of the samples. The films had transition temperatures (T_{c (0)}) of 35 K and irreversibility fields of up to 15 T at 5 K. Transport critical current densities of 3 × 10⁸ A m^-2 were measured at 20 K and 1 T for MgB₂ films on single-crystalline Al₂O₃, whereas 8 × 10⁸ A m^-2 was found for films on polycrystalline Al₂O₃ under the same conditions. Magnetization data and magneto-optical imaging indicated instabilities (flux jumps) at 4.2 K, which disappeared at around 10 K. The critical current densities of all MgB₂ films on either single-crystalline or polycrystalline Al₂O₃ were independent of the orientation of the film with respect to the magnetic field direction.

Document Type: Research article

DOI: http://dx.doi.org/10.1088/0953-2048/17/6/005

Publication date: 2004-06-01