  The periodic response of magnetoresistance to an externally tunable
parameter, such as magnetic field or chemical composition, in the bulk or an
artificially designed material has been exploited for technological
applications as well as to advance our understanding of many novel effects of
solid state physics. Some notable examples are the giant magnetoresistance
effect in layered materials, the quantum hall effect in semiconductor
heterostructure and the phase coherence of electronic wave function in
disordered metals. In recent years, the ability to engineer materials at the
nanoscale has played a key role in exploring new phenomenon. Using a system
involving periodic Co dots array in direct contact with a surrounding
polycrystalline Cu film, we report the observation of giant thermal hysteresis
and an anomalous oscillatory magnetoresistance behavior. The unusual aspects of
oscillatory magnetoresistance include its observation along only one field scan
direction in an intermediate temperature range of 100 K < T < 200 K. Reducing
the thickness of the Cu film weakens the magnetoresistance oscillation. These
properties suggest a new phenomenon, which could be harnessed for future
technological applications.
