Magnetic properties of (C1TEX-TTF)FeBr4(X=S, Se)

The correlation between the magnetic properties and crystal structure of is ostructural pi-d interaction systems (C1TEX-TTF)FeBr4 (X=S, Se) is investig ated by crystal structure analysis and magnetic susceptibility measurements . These salts form a sheet structure consisting of one-dimensional anion zi gzag chains and donor dimers, the latter of which bridge between two anion chains. The susceptibility, to which only Fe3+ (S=5/2) spins contribute as a triangle-based spin ladder system, shows antiferromagnetic phase transiti ons at T-N=4.2K and 3.6K for X=S and Se, respectively Below T-N, weak ferro magnetism appears due to the Dzyaloshinski-Moriya interaction when the fiel d is applied along one of the spin hard-axes. The difference between the tw o salts in the weak ferromagnetic transition suggests that the interaction between two Fe3+ spin ladders is reduced by a half with changing X=S to Se.