  We have studied the magnetoresistance (MR) of thin highly oriented pyrolytic
graphite mesoscopic samples without and with micro-constrictions of different
widths between the voltage electrodes. The MR for fields parallel to the c-axis
shows an anomalous hysteresis loop compatible with the behavior expected for
granular superconductors. The smaller the constriction width the larger is the
anomalous hysteresis and the higher the temperature for its observation. Our
results support the existence of granular superconductivity probably embedded
at interfaces between crystalline graphite regions.
