| e have made YBCO thin film dc SQUIDs on sapphire substrates that operate above 77 K. The YBCO thin films were largely free of weak links and have critical current densities (J;We have also developed a low temperature magnetic force microscope by using piezoresistive cantilevers from room temperature to 6 K in vacuum. We used the frequency modulation technique to detect the magnetic force gradient between an iron-coated tip and the sample. We demonstrated the operation of this new instrument by obtaining images of magnetic domains in 8mm VHS tape at room temperature, 77K and 6K. This microscope is ideally suited for the characterization of thin films of high temperature superconductors. With this microscope, we have obtained images of superconducting vortices on... |
