Thin MgB2 films were fabricated on sapphire substrates by using electron beam deposition, without any post-treatment. The films had columnar grains aligned perpendicular to the film surface. Superconducting properties were investigated in magnetic fields, B, in the range 0 to 28T and/or from 4.2K to the critical temperature, by using the direct-current 4-probe transport method. The TC of the films was 33.12 to 33.90K in self-field. The films exhibited a very high JC at 4.2K: 4.7–7.1 x 106A/cm2 in self-field and 0.8–1.1 and 0.3–0.4 x 106A/cm2 in 4T for perpendicular and parallel fields, respectively. At 4.2K, the films carried 0.4–1.0 and 0.8 x 105A/cm2; in a perpendicular field of 8T and the parallel field, respectively. The JC exceeded 105A/cm2 at 27K in 1T and 15–17K even in 5T (perpendicular fields). The upper critical fields, BC2 and irreversibility fields, Birr, at 4.2K were 27.6–27.9T and 16.7–19.2T in parallel fields, and 17.5–20.4T and 10.7–13.4T in perpendicular fields, respectively. The strong pinning at grain boundaries between columnar grains was confirmed at high temperatures and below 7–8T at 4.2K.

High-Temperature and High-Field Performance of MgB2 Films with JC of 106A/cm2 (4.2K, 4T). H.Kitaguchi, T.Doi: Superconductor Science and Technology, 2005, 18, 489-93