Transport properties of MgB₂ films grown on Hastelloy tape: Substrate temperature effect

Abstract

We report on the transport properties of MgB₂ films that were directly grown on Hastelloy tapes by using a hybrid physical chemical deposition method. The substrate temperatures was varied from 480 °C to 540 °C in 20 °C increment while the deposition time and the gas mixing ratio were kept constant at 10 min and H₂:B₂H₆ = 70:30, respectively. Within this window of substrate temperature, all the samples except the one grown at 480 °C exhibited critical current densities, J _c , much higher than those observed in MgB₂ wires and tapes that were made by using the powder method. For instance, the film grown at 500 °C exhibited a value of J _c exceeding 3 × 10⁵ A/cm² at 4 T and 5 K measured in magnetic fields applied perpendicular to the substrate. In the samples grown at temperatures above 500 °C, a resistance dip was observed in the same field orientation, which can be regarded as evidence for strong flux pinning.