Effects of calcination temperature on structure and magnetic properties of pure FeCo2O4 powders

Abstract A series of FeCo2O4 powders was initially synthesized using a hydrothermal method and subsequently calcined at various temperatures to produce the final product. Pure phase FeCo2O4 powders can only be formed in the temperature range of 950–1050 °C. In this work, we study the cation occupation, cation valence, bond length and bond angle changes of the pure phase FeCo2O4 powders formed in such a narrow temperature range. Octahedral lattice distortion in the pure phase FeCo2O4 samples has been observed. More tetrahedral Fe3+ and octahedral Co2+ are excited and exchanged their sites as the calcination temperature increases from 950 °C to 1000 °C, and part of Co3+ ions are reduced to Co2+ in the sample calcined at 1050 °C. The structure of the sample calcined at 1000 °C is close to that of the ideal FeCo2O4 spinel. Magnetic measurements show that ferrimagnetism and anti-ferromagnetism coexist in the pure phase FeCo2O4 samples. Interaction changes between ferrimagnetism and antiferromagnetism caused by the structural changes of the samples have been studied. Due to the pinning of the local anti-ferromagnetism to ferrimagnetism in the sample, the sample shows a Barkhausen jump below 150 K. As the measurement temperature increases further, the system enters into a reentrant spin glass state.