Magnetic flux relaxation of epitaxial YBa2Cu3O7-δ films at low temperatures

Abstract

In this paper we present magnetic flux relaxation mea critical current Jc measurements on epitaxial coevaporated films of YBa2Cu3O7-δ superconductor. We measured a critical current of 3.5 ∗ 1011 A/m2 at 4.2 K and 1.3 ∗ 1010 A/m2 at 77 K. Jc depends strongly on the magnetic field B for B applied perpendicularly to the surface. The magnetization relaxation M(t) is logarithmic in time. In contrast to single crystals and polycrystalline samples the normalized magnetization relaxation tends towards a constant value at low temperatures and is weakly field-dependent.