Three-dimensional antiferromagnetic transition of iodine-doped fluoro-aluminum phthalocyanine with a disordered polymer chain

A bulk three-dimensional (3D) antiferromagnet of iodinated fluoro-aluminum polymer phthalocyanine AlPcF-I0.87 has been synthesized. A powder x-ray-diffraction analysis indicates that the stoichiometry of the antiferromagnetic phase is AlPcF-I₁ with a tetragonal unit cell of a=13.914±{}0.009 {} and c=7.096±{}0.028 {} and that the array of the cofacially linked phthalocyanine (Pc) rings as well as that of the I atoms has a large disorder along the c direction with a distribution in the c coordinates of ±{}1.14 {} around the average position. The magnetism of the AlPcF-I0.87 is caused by the unpaired spins residing on the AlPcF polymer chain which are produced by the charge transfer from the Pc rings to the iodine. A 3D-antiferromagnetic transition occurs at 80 K, which is evidenced by a quenching of the electron paramagnetic resonance (EPR) signal intensity, an anomalous broadening of the linewidth, and a maximized static susceptibility at this temperature. The angular dependence of the EPR linewidth indicates that the exchange interaction in the system is three dimensional in agreement with the dimensionality of the magnetism. The EPR signal intensity at 300 K is compatible with the localized-spin picture. An interpretation of the results is that the large disorder in the AlPcF chain causes the localization of the spins which is a necessary condition for the magnetic phase transition to occur.