Influence of the inclination of columnar defects on the reversible magnetization of high-T-c superconductors

Reversible magnetization has been studied in crystals of highly anisotropic high-T-c superconductors, containing columnar defects oriented either alon g the c axis or at an angle theta(i) from it. With the magnetic field appli ed along c, a similar dip in the M-vs-ln(B) curves is observed for both tra ck orientations. The location of this dip is shown to be related to B-cd, t he field at which the vortex and track densities per ab plane are the same. The vortex pinning energy, extracted from the low field regime, is found t o be slightly larger for theta(i) = 60 degrees than for theta(i) = 0 degree s. This effect is ascribed to the larger size of the track projections on t he ab planes, in the case of inclined tracks. On the basis of the random na ture of the track distribution, a model is proposed to account for the smoo th character of the crossover between the low field (B much less than B-cd) and high held (B much greater than B-cd) regimes. [S0163-1829(98)04146-0].