Exact Solution for the Critical State in Thin Superconductor Strips with   Field Dependent or Anisotropic Pinning
  An exact analytical solution is given for the critical state problem in long thin superconductor strips in a perpendicular magnetic field, when the critical current density j_c(B) depends on the local induction B according to a simple three-parameter model. This model describes both isotropic superconductors with this j_c(B) dependence, but also superconductors with anisotropic pinning described by a dependence j_c(theta) where theta is the tilt angle of the flux lines away from the normal to the specimen plane. 
Grigorii P. Mikitik and Ernst Helmut Brandt