Inter-molecule interaction for magnetic property of vanadyl tetrakis(thiadiazole) porphyrazine film on Au(1 1 1)

We report scanning tunneling microscope (STM) observation of vanadyl tetrakis(thiadiazole) porphyrazine (VOTTDPz) molecules, which is a family molecule of phthalocyanine (Pc) but without C–H termination in the perimeter, deposited on Au(1 1 1) surface. Well-ordered film corresponding to 4 × 4 superstructure with respect to Au(1 1 1) surface is formed, in which the centers of the molecules are separated by 1.12 nm, which is much smaller than that observed for a VOPc molecule on Au(1 1 1), due to the absence of C–H termination. At the same time, the azimuthal angles of neighboring molecules rotate with each other by 30°. A contrast variation of bright and dark molecules is observed, which are interpreted as O-up and O-down molecules, respectively, based on the density functional theory simulation. Spin-polarized local density of states calculation shows spin-polarized V 3d state, which is delocalized over the ring. Spin detection is executed by measuring Kondo resonance in the tunneling spectroscopy near the Fermi level, which is caused by the interaction of an isolated spin and conduction electron of the substrate. We detected asymmetric and weak Kondo peak for out-of-plane outer magnetic field of 0 T, which becomes strong and symmetric peak at 5 T, which is understood by the shift of the spin center of the Kondo resonance from V 3d to delocalized π state in ring with the magnetic field.