Magnetic properties of Zn0.7Co2.3O4+δ spinel prepared by thermal decomposition of binary oxalates in air

Magnetization and ac susceptibility of two Zn0.7Co2.3O4+δ spinel specimens obtained by decomposition of the binary oxalate Znx Co1–x C2O4·2H2O in air were measured in the temperature range 2–300 K. It is shown that the complex oxide Zn0.7Co2.3O4+δ formed right after the decomposition of the oxalate (at 220 °C) contains about 0.002 mass% metal cobalt, which is responsible for the dependence of the magnetic susceptibility χ on magnetic field at 300 K. Below 100 K, the χ = f (T) dependence of this specimen is characterized by divergence between curves measured under ZFC and FC conditions and a magnetic hysteresis loop at 2 K. The specimen synthesized at 700 °C does not contain a ferromagnetic component and is paramagnetic in the temperature interval 2–300 K. The observed differences in magnetic properties are explained by a higher degree of oxidation of cobalt and the nanodimensional state of the compound formed at a lower temperature. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)