Ferrimagnetism up to 200 K in Ti-rich double perovskites ACu3Ti4−xMnxO12: Role of double exchange mechanism

We report the striking switching of the antiferromagnetic ground state of copper-based double perovskites (Ca/La2/3)Cu3Ti4O12 to the ferrimagnetic state by introduction of small amounts of Mn on Ti-sites. CaCu3Ti3MnO12, La2/3Cu3Ti3.5Mn0.5O12, LaCu3Ti3MnO12, and LaCu3Ti2Mn2O12 were synthesized at normal pressure. These Ti-rich oxides are ferrimagnetic despite their strong magnetic dilution. The 200 K ferrimagnet LaCu3Ti2Mn2O12 exhibits intrinsic magnetoresistance, maximum at TC, which is unique in all the series of double distorted perovskites actually known. These properties are discussed in terms of strong antiferromagnetic superexchange Cu–O–Mn interactions. The role of double exchange in the properties of the mixed valent oxide LaCu3Ti2Mn2O12 is discussed.