Transition-metal-doped phthalocyanines (TMPc, TM = Co, Ni, Cu, V, and Mn, chemical formula: C32H16N8TM) are molecular semiconductors with interesting electrical, optical, and magnetic properties. Consequently, they have been of considerable interest from both fundamental aspects as well as for their potential applications in organic light-emitting diodes (OLED), organic solar cells, nonlinear optical devices, and spintronic devices. In this work, the nature of magnetism in TMPc was investigated by measuring their magnetization and ac magnetic susceptibilities in magnetic fields up to 90 kOe and covering the wide temperature range of 0.5 K to 300 K. These low temperatures and high magnetic field measurements combined with detailed analysis of the data have provided new information about the nature of magnetism of TMPc. Major results include breakdown of the Hund’s rules for CoPc, NiPc and MnPc, presence of the linear chain magnetism but without long range magnetic ordering, antiferromagnetic exchange coupling in CoPc and CuPc, ferromagnetic exchange coupling in MnPc, near perfect paramagnetism in VOPc and diamagnetism in NiPc.

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