Charge Transfer and Disorder in Double Perovskites

The effect of disorder due to anti sites on the charge-transfer processes in the double perovskite Sr2FeMoO6 has been assessed at the microscopic level, using 57Fe Mossbauer spectroscopy. We have followed over a very broad temperature range (from 673 to 4.2 K) the spectral response of three polycrystalline samples only differing in the levels of anti-site disorder of the B sublattice. Our measurements reveal an intricate charge-transfer pattern across TC that is connected to the levels of disorder present in each sample. It is found that the magnetic transition triggers a charge-transfer process between the ordered and anti-site disordered regions for moderate levels of disorder, while this process is completely disabled when disorder becomes dominant. The observed behavior is correlated to the macroscopic properties of the system.