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

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.