Enhancement of Jc of MgB2 thin films by introduction of oxygen during deposition

Abstract

The introduction of various pinning center are examined as the effective means for improvement of Jc of MgB2 thin films. We have investigated the effects of introduction of oxygen during deposition on the superconducting properties of MgB2 thin films.MgB2 thin films were prepared on polished sapphire C(0001) single crystal substrates by using electron beam evaporation technique (EB) without any post-annealing. The background pressure was less than 1.3×10−6Pa. The evaporation flux ratio of Mg was set at 30 times as high as that of B, and the growth rate of MgB2 film was 1nm/s. The film thickness was typically 300nm at 5min deposition. The substrate temperature was 245°C.Under these conditions, we controlled the oxygen partial pressure (PO2) within the range from 1.3×10−6 to 1.3×10−3Pa by using a quadrapole mass spectrometer. Although Tc of deposited thin film decreased in order of PO2, ΔM in the magnetization hysteresis loops measured from 0 to 6T at 4.2K increased up to 1.3×10−5. On the other hand, thin film prepared under PO2 of 1.3×10−3Pa does not show superconducting transition. Between these films, there is no difference in the crystal structure from X-ray diffraction (XRD). These results suggest that the pinning center in the thin films increased by introduction of oxygen. Extremely small amount of oxygen introduction has enabled the control of growth of oxide.