Critical Phenomena of Ferromagnetic Transition in Double-Exchange Systems

Critical phenomena of ferromagnetic transition at finite temperatures are studied in double-exchange systems. In order to investigate strong interplay between charge and spin degrees of freedom, the Monte Carlo technique is applied to include fluctuations in a controlled and unbiased manner. By using finite-size scaling analysis, critical exponents and transition temperature are estimated for a model with Ising spin symmetry in two dimensions. The obtained exponents differ significantly from the mean-field values, but are consistent with those of spin models with short-range exchange interactions. The universality class of this transition belongs to that of short-range interaction with the same spin symmetry. We also discuss the case for three dimensions. The results are compared with experimental results in perovskite manganites which show colossal magnetoresistance.