  Electron spin resonance spectra of copper phthalocyanine doped with alkaline
metals (AxCuPc) have been investigated. The temperature dependence of ESR
spectra indicates the ferromagnetic behavior. The Curie-Weiss temperature
varies from 30K to 115K depending on the stoichiometry x of samples. Some
particles of polycrystalline samples were attracted to a weak magnet at
temperature slightly higher than 77K. The observed magnetism is caused by
unpaired pi-electrons of phthalocyanine anions on the Eg doubly degenerated
molecular orbital. The observed ferromagnetism can be understood within the
framework of the McConnell-2 model proposed for organic ferromagnetic
charge-transfer complexes. The high-temperature magnetism in AxCuPc is
considered to be a result of the Zener mechanism of double exchange between
phthalocyanine molecular anions of different valence.
