  We report a study on the response of superconducitng micro-tracks and quantum
interference devices (SQUIDs) to a proximal SMM film. As a test case,
Langmuir-Blodgett $Mn_{12}$-ac SMM films have been grown on 2 $\mu$m wide Nb
tracks and Nb nano-SQUIDs to observe the proximity effect of magnetic moment
and magnetization tunneling, respectively. The superconducting critical
temperature of thin Nb tracks (thinner than the coherence length of Nb) were
found to decrease by the magnetic moment of $Mn_{12}$-ac SMM. Following the
thermally activated flux flow (TAFF) model, we found an increase in the vortex
unbinding energy of the SMM coated Nb tracks, near critical temperature. More
importantly, the random alignment of moments of the $Mn_{12}$-ac molecules at
low fields seemed to have the enhancing effect on vortex unbinding energy
rather than the saturated state of $Mn_{12}$-ac molecules at high fields. In
the fully superconducting state, on the other hand, the vortex pinning effects
were found to be more effective in the saturated state of the $Mn_{12}$-ac
molecules, as seen from magnetoresistance and field dependent critical current
measurements. In a separate experiment, a Langmuir-Blodgett film of SMM was
grown on a nano-SQUID to look for local changes in magnetization arising from
magnetizatin tunnelling phenomenon in SMMs. Upon magnetizing the SMM (deposited
on SQUIDs) at 2 K along the plane of the film and allowing it to relax, we
found occasional jumps in the underlying SQUID voltage, unlike bare
nano-SQUIDs, which did not show any such jumps over several hours. Therefore,
we believe that the jumps in the SQUID voltage are the signatures of random
tunneling of magnetization in the SMM layer.
