Single-crystal magnetic study on guest-tunable weak ferromagnets [M{N(CN)2}2(pyrimidine)](guest) (M = Fe, Co)

Low-temperature magnets derived from [M {N(CN)(2)}(2)(pm)] (M = Fe-II, Co-II) have guest molecules incorporated in the clearance of the three-dimensional framework, where pm stands for pyrimidine. A pm molecule in [Fe{N(CN)(2)}(2)(pm)](pm) (1) was characterized as a guest by means of X-ray crystallographic analysis. The guest molecules as well as the host N(CN)(2) skeletons are disordered in [Fe{N(CN)(2)}(2)(pm)](guest) (guest = EtOH (2), n-PrOH (3), 1/2 n-BuOH (4)) and also in [Co{N(CN)(2)}(2)(pm)] (guest) (guest = EtOH (5), n-PrOH (6)). The ac and dc magnetic susceptibility measurements on randomly oriented polycrystalline samples of 1-6 revealed that they were weak ferromagnets (canted antiferromagnets) below T-N. The single-crystal magnetization measurements clarified the T-N's and the cant angles at 2 K as follows: T-N = 5.6 K, theta = 1.3degrees (H parallel to c) for 1; T-N = 3.3 K, theta = 16degrees (H parallel to c) for 2; T-N = ca. 2 K, theta = 7.1degrees (H parallel to b) for 5. The magnetic ground state seems to be related with single-ion anisotropy of the metal ions and the spin canting may take place as a combined result of the axial or in-plane anisotropy and antiferromagnetic interaction. The incorporated guest molecule tunes the single-ion anisotropy of the host metal ions, and consequently the magnetic phase transition phenomena were drastically different depending on the guest molecules.