Dramatic variation of the multiferroic properties in Sr doped Ca_1-xSr_xMn₇O₁₂

Abstract

CaMn₇O₁₂ is a magnetic multiferroic material, in which large ferroelectric polarization has reportedly been induced by magnetic ordering. In this work, we observe remarkable changes in the spontaneous ferroelectric polarization PS as well as the magnetization M with only 2% Sr doping. In Ca_0.98Sr_0.02Mn₇O₁₂, P_S dramatically becomes more than double the P_S in the un-doped material and concomitantly M is reduced to less than half of its value therein. Increase of P_S together with the decrease of M points out clearly the coupling of P_S and M in CaMn₇O₁₂. We stress here that as Ca and Sr are isovalent, no charge carriers (electrons and holes) are added in the system due to Sr-doping. X-ray diffraction shows that all our Sr-doped materials Ca_1-xSr_xMn₇O₁₂ (x = 0.01, 0.02, 0.05, 0.10) are free from secondary phases. From our work, it becomes clear why SrMn₇O₁₂ exhibits no or weak ferroelectricity.