Ferrimagnetic and relaxor ferroelectric properties of R2MnMn(MnTi3)O12 perovskites with R = Nd, Eu, and Gd

Abstract

ABO₃ perovskites have a number of ferroelectric instabilities resulting in varieties of long-range and short-range polar distortions. On the other hand, polar distortions are very limited in quadruple perovskites AA′₃B₄O₁₂ and A₂A′A′′B₄O₁₂. Here we showed that R₂MnMn(MnTi₃)O₁₂ oxides, belonging to a family of A-site columnar-ordered quadruple perovskites, exhibit relaxor-like ferroelectric properties slightly below room temperature. They were synthesized by a high-pressure high-temperature method for R = Nd, Eu, and Gd at about 6 GPa and 1570 K. At room temperature they crystallize in centrosymmetric space group P4₂/nmc (no. 137), and their crystal structures were studied by synchrotron powder X-ray diffraction. They exhibit broad dielectric anomalies just below room temperature with characteristic frequency-dependent features of the relaxor ferroelectric behavior. P–E loop measurements at 77 K confirmed ferroelectricity for R = Nd and Eu. Magnetic and specific heat measurements showed the presence of long-range ferrimagnetic transitions below 20 K (R = Nd), 30 K (R = Eu), and 42 K (R = Gd). Additional specific heat anomalies were observed below about 5 K for R = Nd and Gd probably due to the involvement of rare-earth cations in long-range orderings. The coexistence of ferrimagnetic transitions and relaxor-like ferroelectric properties make R₂MnMn(MnTi₃)O₁₂ perovskites multiferroic materials.