Field dependence of the Hall effect in the organic superconductors κ-(BEDT-TTF)2Cu[N(CN)2]Cl1 − xBrx

Hall voltage versus magnetic field curves were found to be nonlinear and to have temperature-dependent shape in the organic superconductors κ-(BEDT—TTF)2Cu[N(CN)2]Cl1 − xBrx (BEDT—TTF = bis(ethylenedithio)tetrathiafulvalene). Close relation between the shape of the curves and structural anomalies in the salts was disclosed. The nonlinearity is assigned to magnetic ordering, causing or accompanying structural transformation. Changes of the Hall effect field dependence were used together with magnetic viscosity phenomena to plot a phase diagram of the salts. The main lines of the diagram could be traced through all compositions, irrespective of their resistance behavior. The results cast doubt on the decisive role of purely electronic instabilities in phase transformations in the material and are discussed in relation to the origin of magnetic order.