Effect of chemical pressure induced by La3+/ Y3+ substitution on the magnetic ordering of (A Mn3) Mn4 O12 quadruple perovskites

We report on the successful high-pressure synthesis of single-phase powders of the quadruple perovskite (YMn3)Mn4O12, where the chemical pressure exerted by the small Y3+ ion is expected to enhance the exchange interaction between Mn3+ ions. According to this expectation, powder neutron diffraction, specific heat, and magnetization measurements give evidence of a C-type antiferromagnetic ordering of the Mn3+ ions in the octahedrally coordinated B sites at TN,B=108K, 30 K higher than in the isostructural and isovalent compound, (LaMn3)Mn4O12. Surprisingly, we found no evidence of long-range magnetic order of the square-coordinated A′ sites, although an indication of latent magnetic order is given by a broad peak of the DC magnetization between 70 and 40 K and by a sharp peak in the AC susceptibility at T∗=70K. A further unexpected feature of (YMn3)Mn4O12, not found in previously reported (AMn3)Mn4O12 compounds, is a second-order structural phase transition at Ts=200K, attributed to a partial redistribution of charge involving both the B and A′-site Mn3+ ions. The present results suggest the existence of competing magnetic orderings, which may be linked to the occurrence of magnetic ferroelectricity in the (AMn3)Mn4O12 system.