Magnetic properties of Zn 0.7 Co 2.3 O 4+ δ spinel prepared by thermal decomposition of binary oxalates in air

Magnetization and ac susceptibility of two Zn 0.7 Co 2.3 O 4+ δ spinel specimens obtained by decomposition of the binary oxalate Zn x Co 1– x C 2 O 4 ·2H 2 O in air were measured in the temperature range 2–300 K. It is shown that the complex oxide Zn 0.7 Co 2.3 O 4+ 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)