Magnetic Properties of (C1TEX-TTF)FeBr4(X˭S, Se)

Abstract

The correlation between the magnetic properties and crystal structure of isostructural π-d interaction systems (C₁TEX-TTF)FeBr₄ (X˭S, Se) is investigated by crystal structure analysis and magnetic susceptibility measurements. These salts form a sheet structure consisting of one-dimensional anion zigzag chains and donor dimers, the latter of which bridge between two anion chains. The susceptibility, to which only Fe^3± (S=5/2) spins contribute as a triangle-based spin ladder system, shows antiferromagnetic phase transitions at T_N=4.2K and 3.6K for X˭S and Se, respectively. Below T _N, weak ferromagnetism appears due to the Dzy-aloshinski-Moriya interaction when the field is applied along one of the spin hard-axes. The difference between the two salts in the weak ferromagnetic transition suggests that the interaction between two Fe^3± spin ladders is reduced by a half with changing X˭S to Se.