  We characterize molecular magnet heterojunctions in which sublimated CoPc
films as thin as 5 nm are sandwiched between transparent conducting
bottom-layer indium tin oxide and top-layer soft-landing eutectic GaIn (EGaIn)
electrodes. The roughness of the cobalt phthalocyanine (CoPc) films was
determined by atomic force microscopy to be on the order of several nanometers,
and crystalline ordering of lying-down planar molecules was confirmed by X-ray
diffraction. The current-voltage (I-V) characteristics reveal the onset of a
superconducting gap at Tc = 6 K, which together with higher temperature fits to
a modified Simmons' model, provide incontrovertible evidence for direct quantum
mechanical tunneling processes through the magnetic molecules in our
heterojunctions. The voltage dependent features in the differential conductance
measurements relate to spin states of single molecules or aggregates of
molecules and should prove to be important for quantum information device
development.
