Weak ferromagnetic response of d electrons and antiferromagnetic response of π electrons in TPP[Mn(Pc)(CN)₂]₂ in torque magnetometry experiments

We have investigated the magnetic properties of TPP[Mn(Pc)(CN)2]2 by the cantilever magnetometry technique. This technique enables us to extract information on the magnetism even if the sample is very small (1 μg). The torque curve measured when the magnetic field (≤7 T) is rotated in a plane that includes the c-axis shows a signature that is characteristic of weak ferromagnetism. The electron responsible for this behavior should be the d electron of the Mn³⁺ ion. On the other hand, when the field is rotated in the ab-plane, the torque curve exhibits an antiferromagnetic signature. The electron responsible for this behavior should be the π electron. Taking the susceptibility data into account, we have proposed two models of the spin configuration for d electrons: canted antiferromagnetism, and the field-induced ferromagnetic alignment. We have pointed out that even in the canted antiferromagnetic case, the torque curve is the same as that in the ferromagnetic case if the anisotropy energy is very small. These models do not contradict the experimental observation that magnetoresistance is hardly seen in TPP[Mn(Pc)(CN)₂]₂ if the interaction between π and d electrons is weak.