Detection of new superconductors using phase-spread alloy films

We describe an effective method for discovery of new superconductors, which combines phase-spread alloy thin film preparation with a magnetic field modulated ~MFM! microwave absorption technique. The MFM technique can detect superconductivity in YBa2Cu3O72d volumes as small as 5310 cm. As an illustration, PrxGd12xBa2Cu3O72d thin films with varying x were simultaneously grown on the same substrate using a phase-spread alloy technique. The onset temperature determined from the microwave absorption agrees with resistivity, Auger spectroscopy, and energy-dispersive x-ray microanalysis data. When phase-spread Lax~NiB!12xNy films (0,x,1) were grown at several different N partial pressures and temperatures, no superconductivity was detected except that of pure La. In contrast, superconductivity was detected in Yx~NiB!12xCy films grown on MgO. © 1995 American Institute of Physics.