Critical current control in a superconducting thin film with a ferromagnetic layer

We report suppression of the critical current of thin film YBa/sub 2/Cu/sub 3/O/sub 7/ layers by altering the magnetization of a ferromagnetic La/sub 0.67/Ca/sub 0.33/MnO/sub 3/ overlayer. We provide evidence that the critical current suppression is related to the spin-polarized state of the magnetic layer, rather than a direct magnetic influence. We argue that the spin diffusion length in the superconducting layer is small compared with the typical domain size in the ferromagnetic layer in its demagnetized state.