Variable sample temperature scanning superconducting quantum interference device microscope

We demonstrate a design for a scanning superconducting quantum interference device (SQUID) microscope in which the sample temperature can be varied over a large range. In this design, both sample and SQUID are in the same vacuum space, separated by a few microns. By firmly anchoring the SQUID to a low-temperature bath, the sample temperature can be changed while the SQUID remains superconducting. This allows magnetic imaging at varying sample temperatures with micron-scale spatial resolution and the sensitivity of a low-T-c SQUID. We demonstrate this approach by imaging the temperature dependence of Abrikosov vortices in thin films of the high-temperature superconductor YBa2Cu3O7-delta. We extract the in-plane penetration depth lambda(ab)(T) in our samples from these measurements. (C) 1999 American Institute of Physics. [S0003-6951(99)04026-7].