Abstract
The magnetic state of A-site Cu2+ sublattice is sensitive to the non-magnetic B-site cations in A'A3B4O12 as revealed from ferromagnetic CaCu3M4O12 (M = Sn and Ge) and antiferromagnetic CaCu3Ti4O12. We report the sensitivity of Cu2+ ordering when part of it is substituted by Mn3+ keeping the B-site cations non-magnetic. We observed that mixed occupancy of Cu2+ and Mn3+ in A-site, long-range ordering of Cu2+ is remarkably destabilized in (Ca/La/Y)Cu3-xMnxTi4-yAlyO12 (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 CaCu3Ti4O12 is drastically suppressed in CaCu2MnTi3AlO12. Introduction of Mn3+ in Cu2+ sublattice largely hampers the Cu2+—Cu2+ 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 Cu2+ and Mn3+ spins though they occupy the same crystallographic sites. LaCu3Ti3AlO12 and La2/3Cu2.5Mn0.5Ti3.5Al0.5O12 show rather similar behaviour. LaCu3Ti3AlO12 shows prominent difference in magnetization compare to La2/3Cu3Ti4O12, whereas YCu3Ti3AlO12 does not with respect to Y2/3Cu3Ti4O12. The differential magnetic behaviour is possibly due to the size difference between La and Y. The ac-susceptibility measurement in LaCu3Ti3AlO12 suggests the formation of short-range ordered magnetic clusters above TN in the paramagnetic phase and there is no evidence of spin glass-like behaviour at low temperature.
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