Ti-rich double perovskites LnCu_3−yTi_2−xMn_2+x+yO₁₂ : ferrimagnetism and magnetoresistance up to room temperature

Abstract

Ti-rich double perovskites LnCu_3−yTi_2−xMn_2+x+yO₁₂ have been synthesized at normal pressure, with a wide homogeneity range, 0 < x < 0.5 and 0 < y ≤ 1. All these oxides are ferrimagnetic, with T_C ranging from 160 K to 293 K, in spite of the high 3d0-Ti content in the octahedral sites. The evolution of T_C can be monitored on the basis of three factors-antiferromagnetic superexchange interactions Cu²⁺↑–O–Mn³⁺/4+↓–O–Cu²⁺↑, double exchange Mn⁴⁺–O–Mn³⁺ interactions in the octahedral sites and chemical pressure due to the size effect of Ln3+. Differently from high pressure synthesized manganites, these oxides exhibit maximum magnetoresistance at T_C, similar to single perovskite manganites. Intrinsic magnetoresistance can thus be obtained at room temperature, but with a smaller amplitude compared to single manganites, due to the dilution effect of titanium.