Smaller rare-earth cation and mixed valent Mn incorporation as a dual strategy to enhance ferrimagnetic ordering temperatures in A-site ordered quadruple perovskites, LnCu3Mn1+xTi3-xO12 (Ln = La, Nd; x=0, 0.3)

High-T-C ferro-/ferrimagnetic quadruple perovskites constitute an important class of oxides that has garnered a lot of research attention in recent times, but their synthesis is commonly achieved under high-pressure conditions. Thus, the development of high-T-C quadruple perovskites that can be synthesized under ambient pressure can be a key to the above problem. Herein, we report ambient pressure synthesis of a series of new A-site ordered quadruple perovskites, LnCu(3)Mn(1+x)Ti(3-x)O(12) (Ln = La, Nd; x = 0, 0.3), by coupled aliovalent-cation manipulation in CaCu3Ti4O12. The effect of smaller lanthanide Nd incorporation in place of La has been investigated. Furthermore, 30% mixed valency of Mn per Mn3+ has been introduced in place of Ti4+ following similar strategies adopted to achieve giant magnetoresistive manganites La(0.7)A(0.3)MnO(3) (A = Ca, Sr, Ba) from LaMnO3. Mn is present in the 3+ state for x = 0 and in a mixed valent state (3+ and 4+) for x = 0.3, whereas Cu exists in the 2+ state in all the compounds. While LaCu3MnTi3O12 and LaCu3Mn1.3Ti2.7O12 show the onset of ferrimagnetic order at similar to 60 and 110 K, respectively, the corresponding Nd analogs, NdCu3MnTi3O12 and NdCu3Mn1.3Ti2.7O12, exhibit enhanced T-C's of similar to 80 and 140 K, respectively. This work reveals an effective strategy of mixed-valent Mn incorporation in the B-sublattice and smaller rare-earth cation incorporation to achieve higher ferrimagnetic ordering temperatures in quadruple perovskites.