Extreme magnetic anisotropy and multiple superconducting transition signatures in a [Nb(23Â nm)/Ni(5Â nm)]5 multilayer

We have applied polarized neutron reflectometry, and novel SQUID and vibrating reed magnetometry to probe a [Nb(23 nm)/Ni(5 nm)]5 multilayer (ML) whose superconducting state magnetic anisotropy is dominated by confined (in-plane) supercurrents in DC magnetic fields, H, applied nearly parallel to the ML plane. The upper critical field exhibits abrupt shifts (0.1-0.6 K) in near-parallel fields, but is field-independent for μ0H < 0.8 T when the ML is exactly aligned with the DC field, indicating suppression of orbital pairbreaking and the possible presence of unconventional superconducting pairing states.