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

A series of FeCo 2 O 4 powders was initially synthesized using a hydrothermal method and subsequently calcined at various temperatures to produce the final product. Pure phase FeCo 2 O 4 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 FeCo 2 O 4 powders formed in such a narrow temperature range. Octahedral lattice distortion in the pure phase FeCo 2 O 4 samples has been observed. More tetrahedral Fe 3+ and octahedral Co 2+ are excited and exchanged their sites as the calcination temperature increases from 950 °C to 1000 °C, and part of Co 3+ ions are reduced to Co 2+ in the sample calcined at 1050 °C. The structure of the sample calcined at 1000 °C is close to that of the ideal FeCo 2 O 4 spinel. Magnetic measurements show that ferrimagnetism and anti-ferromagnetism coexist in the pure phase FeCo 2 O 4 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.