Preparation and characterization of superconducting MgB2 films on alumina
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 (Tc (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
Publication date: June 1, 2004