nel barrier layer of an electrically insulating material, e.g. Al2O3, or may be used in a giant magnetoresistive device, in which case the spacer layer structure 9 includes a layer of a non-magnetic material, e.g. Cu. [0038] The thin non-magnetic layer structure 5 having a thickness of smaller than 3 nm may include one or more layers of a non-magnetic material, such as the elements Cu, Ru or Ta, o