Effect of incoherent interaction between A-site Cu2+ and Mn3+ on magnetic properties of B-site non-magnetic A′A3B4O12 quadruple perovskite

The magnetic state of A-site Cu ²⁺ sublattice is sensitive to the non-magnetic B-site cations in A`A ₃B ₄O ₁₂ as revealed from ferromagnetic CaCu ₃M ₄O ₁₂ (M = Sn and Ge) and antiferromagnetic CaCu ₃Ti ₄O ₁₂. We report the sensitivity of Cu ²⁺ ordering when part of it is substituted by Mn ³⁺ keeping the B-site cations non-magnetic. We observed that mixed occupancy of Cu ²⁺ and Mn ³⁺ in A-site, long-range ordering of Cu ²⁺ is remarkably destabilized in (Ca/La/Y)Cu _3-xMn _xTi _4-yAl _yO ₁₂ (x/y = 0, 0.5 and 1.0). Samples are characterized by powder X-ray diffraction, FE-SEM imaging, EDX analysis, XPS analysis, Raman spectroscopy and magnetization. The antiferromagnetic ordering of CaCu ₃Ti ₄O ₁₂ is drastically suppressed in CaCu ₂MnTi ₃AlO ₁₂. Introduction of Mn ³⁺ in Cu ²⁺ sublattice largely hampers the Cu ²⁺—Cu ²⁺ interaction. This result is in strong contrast to the system with magnetic cations at B-site. This may be attributed to the incoherent interaction between Cu ²⁺ and Mn ³⁺ spins though they occupy the same crystallographic sites. LaCu ₃Ti ₃AlO ₁₂ and La _2/3Cu _2.5Mn _0.5Ti _3.5Al _0.5O ₁₂ show rather similar behaviour. LaCu ₃Ti ₃AlO ₁₂ shows prominent difference in magnetization compare to La _2/3Cu ₃Ti ₄O ₁₂, whereas YCu ₃Ti ₃AlO ₁₂ does not with respect to Y _2/3Cu ₃Ti ₄O ₁₂. The differential magnetic behaviour is possibly due to the size difference between La and Y. The ac-susceptibility measurement in LaCu ₃Ti ₃AlO ₁₂ suggests the formation of short-range ordered magnetic clusters above T _N in the paramagnetic phase and there is no evidence of spin glass-like behaviour at low temperature.