Anisotropy of pinning forces in NbTi

For wire samples of cold worked Nb- 40wt%Ti and Nb-50wt%Ti a strong anisotropy of the volume pinning force Fpis observed, when the angle between transport current and external magnetic field is varied. Good agreement with the experimental results is found, if Fpdepends on fp², where fpis the pinning force per pinning centre, and if one takes into account the finite dimensions of the subbands that act as pinning centres. For the current-optimized samples, a smaller anisotropy is seen, and for recrystallized samples the pinning force is practically independent of the orientation of current and field, as it was expected.