Generation of high spin state in the spinel Co3O4 nano-domains through interfacial induction

Abstract

The heterogeneous complex oxide, (1 - x)La-xSr-Co oxides (0.8 ≤ x ≤ 0.99), is observed to possess soft ferromagnetic behaviour at ambient temperature, whereas the corresponding perovskite La1-xSrxCoO3-δ solid solution no longer owns magnetic trait at the same temperature. This complex oxide comprises primarily of spinel Co3O4 phase, cubic SrO phase and perovskite La1-αSrαCoO3-β (α ≪ x) phase. Since both pristine spinel Co3O4 and pervoskite structure possess paramagnetic properties at room temperature, the unique ferromagnetic response is interpreted as the result of interfacial induction, presumably through the Jahn-Teller distortion that happened at the octahedral interstices of spinel Co3O4 adjacent to the SrO phase. This perspective was further inferred by XRD, ESR and HR-TEM testing. The HR-TEM images exhibit the interpenetrating SrO and Co3O4 phases with sizes in nano-scale. The existence of a sufficiently large interface is critical to ensure the induction effect to be detected experimentally. Such an extremely high extent of mixing was attained by pyrolysing the metallo-organic chelating gel containing the above three types of metal ions. Besides the interfacial induction effect, an optimum content of La2O3 (1 - x = 0.05) has been verified to play a doping effect, which enhances the response of the spinel Co3O4 nano-phase to the interfacial induction. © 2005 Elsevier B.V. All rights reserved.