Competition between single ion and single chain magnetism in stoichiometric spin chain oxides [Sr4Mn2CoO9]n [Sr5Mn3CoO12]

Abstract

Stoichiometric spin chain “Mn4+-Co2+” oxides [Sr4Mn2CoO9]n[Sr5Mn3CoO12] have been synthesized for n ​= ​1, 2, 3, 4, 5, ∞. The X-ray powder diffraction study of these oxides also formulated Sr1+x(Mn1-xCox)O3, shows that their hexagonal aperiodic structure (a≈9.6 ​Å, c1 ​~ ​2.6 ​Å, c2 ​~ ​3.9 ​Å; modulation vector q ​= ​γc1∗, with γ ​= ​c1/c2) consists of blocks of multiple (n) Mn2CoO9 trimeric units that alternate with single Mn3CoO12 tetrameric units. Competition between single ion (SIM) and single chain magnetism (SCM) is established from ac-susceptibility magnetic measurements: introduction of tetrameric units in trimeric chains hinders SIM signal which decreases with n and disappears for n ​= ​1. A model is proposed for the origin of SIM based on the presence of [Mn4+2Co2+Mn4+2O18]18−groups in the structure. This scheme is supported by the SIM signal observed for the n ​= ​∞ member Sr2Ca2Mn2Co0.5Zn0.5O9 that contains a majority of isolated [Mn4+2Co2+Mn4+2O18] groups.