Anomalousg-Anisotropy in the ESR Signals of Halogen-Doped AlPcF Thin Films

Iodine and bromine doped fluoro-aluminum polymer phthalocyanine (AlPcF) thin films are studied by electron spin resonance (ESR). An anomalous g -anisotropy is observed in the ESR spectra of the AlPcF-I 0.1 and the AlPcF-Br 0.3 films in which the resonance frequencies of the spins are averaged to the mean value corresponding to g =( g ⊥ + g // )/2. The mechanism of the averaging is the spin diffusion along the string-like winding crystallite caused by the exchange interaction. The films after heat treatment do not involve the averaging, and their ESR line widths have the angle dependence of Γ=Γ 0 +Γ 1 (1+cos 2 θ), indicating that the exchange interaction is three dimensional. Both the I-doped and the Br-doped films with and without the heat treatment exhibit 3D-antiferromagnetic transition at around 200 K.