PREPARATION AND MAGNETIC-PROPERTIES OF MANGANESE(II) PHTHALOCYANINE THIN-FILMS

We report the molecular beam epitaxy (MBE) growth of the manganese(II) phthalocyanine thin films with unique crystal structure and the measu rement of their magnetic properties. The epitaxial films were grown on hydrogen-terminated Si(111) substrates. Reflection high energy electr on diffraction observations showed that the crystal structure of the f ilms is different from that of the bulk crystal. A large magnetic anis otropy was observed in the measurements with the SQUID magnetometer. T he films did not show canted ferromagnetism which is usually observed in the beta-type crystal of manganese phthalocyanine. The magnetic sus ceptibility measured with magnetic field normal to the substrate obeye d the Curie-Weiss law with a negative Curie-Weiss constant, indicating the existence of the antiferromagnetic interaction. The negative Curi e-Weiss constant was also observed in disordered films of manganese ph thalocyanine. The variation of magnetic properties between the bulk cr ystal and the films is explained in terms of the difference in superex change interaction caused by microscopic modification of the crystal s tructure, i.e., the stacking arrangement of the molecules. (C) 1998 Am erican Institute of Physics.