Quenched disorder suppression of the first-order magnetic phase transition in manganites

The role of quenched disorder on the magnetic phase transition of ferromagnetic manganites is investigated through the field and pressure dependence of magnetization around T-C. Our results demonstrate that moderate-small chemical disorder promotes second-order behavior. This can be rationalized on the basis of a simple thermodynamic model in which the magnetic order parameter is coupled to the lattice, this coupling being sensitive to chemical disorder. A plausible microscopic scenario is also discussed.