Transport properties of c-oriented MgB2 thin films grown by pulsed laser deposition

The electronic anisotropy in MgB2, which arises from its layered crystal structure, is not completely clear until now. High quality c-oriented films offer the opportunity of studying such property. MgB2 thin films were deposited by using two methods both based on room temperature precursor deposition (by pulsed laser ablation) and ex situ annealing in Mg atmosphere. The two methods differ for the starting targets: stoichiometric MgB2 in one case and Boron in the other. The two films presented in this paper are grown by means of the two techniques on MgO substrates and both are c-oriented; they present Tc values of 31.5 and 37.4 K, respectively. Upper critical field measurements, up to 9 T, with the magnetic field in perpendicular and parallel directions in respect to the film surface evidenced anisotropy ratios of 1.8 and 1.4, respectively. In this paper we will discuss this remarkable and surprising difference also in comparison with the literature data. \ua9 2002 Elsevier Science B.V. All rights reserved