Diamagnetic Molecules Exhibiting Room-Temperature Ferromagnetism in Supramolecular Aggregates

Abstract

Molecule-based materials exhibiting room-temperature ferromagnetism and semiconducting property are promising for molecular spintronic applications. Chemically tunable electronic and magnetic properties of metallo-phthalocyanine (MPc) molecules make them potential candidates in the frame. Here, we show room-temperature ferromagnetism in supramolecular aggregates of two diamagnetic MPcs, nickel(II) phthalocyanine (NiPc; S = 0) and zinc(II) hexadecafluorophthalocyanine (ZnFPc; S = 0). In the magnetization versus applied field (M-H) plot, recorded at room temperature, the supramolecular NiPc---ZnFPc aggregate revealed a clear hysteresis loop with coercive field (Hc) of ?180 Oe. The Hc values were further increased with decreasing the temperature down to 95 K. The direct current (DC) electrical conductivity value of the supramolecular NiPc---ZnFPc system was observed to be significantly higher than that of a mechanical mixture of NiPc+ZnFPc. An optical band gap of ?1.25 eV for the supramolecular solid was estimated from the Tauc plot, and no appreciable charge-transfer interaction between NiPc and ZnFPc was detected. The origin of such unusual ferromagnetism is understood with the help of Goodenough-Kanamori-Anderson (GKA) empirical rules and the Zener model of sp-d exchange interaction.