Magnetic-field-modulated microwave reflectivity of high- T-c superconductors studied by near-field mm-wave microscopy

We report local studies of magnetic-field-modulated microwave reflectivity (MFMMR) of high-T-c superconductors using a near-field scanning aperture pr obe operating at 96 GHz. The MFMMR signal appears as a sharp peak at transi tion temperature and is very useful in identifying superconducting phases i n multiphase samples. We show that MFMMR is qualitatively different from su ch a routine characterization tool as inductive technique. Simultaneous MFM MR and inductive measurements allow us to distinguish between the surface a nd bulk superconducting properties. The MFMMR technique may be easily exten ded for the study of giant magnetoresistance materials. (C) 1999 American I nstitute of Physics. [S0003- 6951(99)01838-0].