Exploration of spin state and exchange integral of cobalt ions in stoichiometric ZnCo2O4 spinel oxides

This work reports on spin state and exchange integral of cobalt ions in stoichiometric ZnCo2O4 nanoparticles with varying particle size from about 24 to 105 nm. Cobalt ions in ZnCo2O4 nanoparticles are present as trivalence in mixed spin state. The effective magnetic moment is distributed in the range of 2.1 ∼ 1.31 μB at room temperature with coarsening of nanoparticles. Further, it is demonstrated that stoichiometric ZnCo2O4 undergoes a magnetic transition from paramagnetism to antiferromagnetism with decrease of temperature, showing a transition temperature of about 5 K. The standard molar entropy and enthalpy for 24 nm ZnCo2O4 are 170.6 ± 1.7 J K−1 mol−1 and 28.2 ± 0.3 kJ mol−1 at 298.15 K, respectively. Based on the heat capacity data, the exchange integral is determined to be 4.16 × 10−22 J. The results report here are really important for further understanding the magnetic and electronic properties of spinel oxides.