Linear chain compounds: Metamagnetism in Co(pyr)2Cl2, Fe(pyr)2Cl2, Fe(pyr)2(NCS)2 and Ni(pyr)2Cl2

We report the observation of low field metamagnetic behavior in powder samples of Co(pyr)2Cl2, Fe(pyr)2Cl2, Fe(pyr)2(NCS)2 and Ni(pyr)2Cl2 where pyr=pyridine. These materials have linear chain structures with strong ferromagnetic interactions along the chains, and relatively weak antiferromagnetic interactions between chains. In all four compounds the transitions were observed as a rapid increase in the magnetic moment with increasing magnetic field. In Fe(pyr)2Cl2, Fe(pyr)2(NCS)2, and Ni(pyr)2Cl2, the transitions at 4.2 K were observed at 0.7 kG, 1.1 kG and 2.7 kG respectively. In the Co compound the transition (at ∠0.7 kG) was observed for T<3K(TN=3.17K). Differential magnetic moment measurements in Fe(pyr)2Cl2 and Fe(pyr)2(NCS)2 are presented. Above the low field transitions the magnetic moment continues to increase and saturation is not achieved for applied fields up to 200 kG. High field Mossbauer data consistent with these results are discussed.