Magnetic Torque Experiments on TPP[Fe(Pc)L2]2(L = Br and Cl): Antiferromagnetic Short-Range Ordering ofdElectrons, Antiferromagnetic Ordering of π Electrons, and Anisotropy Energy

Abstract

We have measured the magnetic torque of TPP[Fe(Pc)Br2]2 and TPP[Fe(Pc)Cl2]2 to clarify their magnetic state, comparing our results with those of formerly performed experiments on TPP[Fe(Pc)CN2]2. The conductors in this family exhibit giant negative magnetoresistance. We employed the cantilever magnetometry technique with our newly developed calibration method to obtain absolute values of the torque (J/rad Fe mol), enabling the comparison between experimental and calculated results. With decreasing temperature, the antiferromagnetic ordering of the π electron is found to occur at \({\sim}13\) K, and then the antiferromagnetic short-range ordering of the \(d\) electron follows at \({\sim}8\) K in these two salts. Our anisotropic one-dimensional Heisenberg model can explain 1) the susceptibility data quantitatively, 2) the torque curves quantitatively, which were obtained when the magnetic field was rotated in the \(ac\)-plane, and 3) the behavior of the \(d\) electron in the torque curves qualitatively, whi...