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 ov er a large range. In this design, both sample and SQUID are in the same vac uum space, separated by a few microns. By firmly anchoring the SQUID to a l ow-temperature bath, the sample temperature can be changed while the SQUID remains superconducting. This allows magnetic imaging at varying sample tem peratures with micron-scale spatial resolution and the sensitivity of a low -T-c SQUID. We demonstrate this approach by imaging the temperature depende nce of Abrikosov vortices in thin films of the high-temperature superconduc tor YBa2Cu3O7-delta. We extract the in-plane penetration depth lambda(ab)(T ) in our samples from these measurements. (C) 1999 American Institute of Ph ysics. [S0003-6951(99)04026-7].