Abstract. An important predicted, but so far uncharacterized, property of the new superconductor MgB₂ is electronic anisotropy arising from its layered crystal structure. Here we report on three c-axis oriented thin films, showing that the upper critical field anisotropy ratio H_c2/H_c2^⊥ is 1.8 to 2.0, the ratio increasing with higher resistivity. Measurements of the magnetic field-temperature phase diagram show that flux pinning disappears at H*0.8H_c2^⊥(T) in untextured samples. H_c2(0) is strongly enhanced by alloying to 39 T for the highest resistivity film, more than twice that seen in bulk samples.

Print publication: Issue 6 (June 2001)
Received 30 April 2001