Abstract
The critical current density Jc and the magnetic relaxation (‘creep’) properties
have been studied for a set of NdBa2Cu3O7- (NdBCO) films doped with BaZrO3 (BZO)
nanoparticles to form columnar defects. The dependence of Jc on the magnitude and
orientation of the applied magnetic field Happ (0 – 6.5 T); and temperature T (5 K – Tc)
was investigated. The normalized flux-creep rate S = −d ln(J ) / d ln(t) was determined
as a function of T. The current dependence of the effective activation energy Ueff(J) was
derived using the formalism developed by Maley. The results are well described by an
inverse power-law type barrier of the form 0 0 ( ) ~ ( / ) eff U J U J J μ with fitted values for
the pinning energy scale U0 and the glassy exponent μ. When comparing values for these
parameters in the BZO-doped samples with those for their undoped control counterparts,
the most striking difference is the larger scale of current density J0 in the doped samples
(a factor of 2.4 higher), while the other pinning parameters do not differ strongly. In the
BZO-doped materials, the pinning energy scale U0 increases with vortex density and J0
decreases, with both following simple power law dependencies on field.