Investigation of the role of morphology on the magnetic properties of Ca2Mn3O8 materials

Abstract

Ca₂Mn₃O₈ exhibits a complex layered structure comprised of Mn₃O₈⁴⁻ layers separated by Ca²⁺ ions. In contrast with the more traditional triangular delafossite layered materials the Mn₃O₈⁴⁻ layers additionally exhibit an ordered vacancy, which forms a ‘bow-tie’ like arrangement of the Mn⁴⁺ ions. We report a comprehensive study of the magnetic properties of a series of Ca₂Mn₃O₈ materials with different morphologies. EXAFS and XANES analysis confirm no differences in either manganese environment or oxidation state between materials. Apparent differences in magnetic order from SQUID magnetometry can be rationalised by uncompensated surface spins arising as a result of changes to the surface to volume ratio between morphologies. Furthermore, these data suggest these materials are potentially frustrated in nature, due to the triangular connectivity of Mn⁴⁺ spins, with a simple ‘spin-up/spin-down’ (↑↓) antiferromagnetic model unable to explain the data collected.