Effect of correlated disorder on the magnetism of double exchange systems

We study the effects of short-range-correlated disorder arising from chemical dopants or local lattice distortions on the ferromagnetism of 3d double exchange systems. For this, we integrate out the carriers and treat the resulting disordered spin Hamiltonian within a local random phase approximation, whose reliability is shown by direct comparison with Monte Carlo simulations. We find large-scale inhomogeneities in the charge, couplings, and spin densities. Compared with the homogeneous case, we obtain larger Curie temperatures (T-C) and very small spin stiffnesses (D). As a result, the large variations of D/T-C measured in manganites may be explained by correlated disorder. We also provide a microscopic model for Griffiths phases in double exchange systems.