Transport properties of c-axis oriented MgB₂ thin films

We have fabricated MgB₂ thin films on a (1 1̄ 0 2) Al₂O₃ substrate by using pulsed laser deposition technique. The thin films had a c-axis-oriented crystal structure normal to the substrate surface, which was confirmed by the x-ray diffraction patterns. The onset transition temperature was 39 K and transition width of ∼ 0.2 K is very sharp. We observed high critical current densities (J_c) of ∼ 16 MA/cm² at 15 K under a self field. The extrapolated value of J_c at 5 K was estimated to be ∼ 40 MA/cm², which is the highest reported for the MgB₂ compound. Due to the very high J_c, this compound would be a promising candidate for practical applications at high temperature and lower power consumption. The formation of vortex-glass phase due to the drastically enhanced pinning force of the vortex is the possible origin of this high value of J_c.