Tunability of crossover phases in MX-compounds

MX materials offer the unique opportunity to study a whole variety of phases from CDW phases over long-range mixed phases to SDW phases by changing the chemical composition, or by applying external pressure. Especially in the regime of the mixed, long wavelength phases, where the free energy differences are small, a magnetic field can be used to select a specific phase characterized by certain charge and spin correlations. We discuss the characteristics of those phases and their relevant parameters regimes and experimental signatures. Since the free energy differences between various phases are small we also discuss the influence of non-adiabaticity and disorder on their relative stability.