Magnetic and magnetocaloric properties of SrFe0.5Co0.5O3-y upon oxidation and reduction: a heterogeneous distribution of the oxidation states
Résumé
The electrochemical oxidation of SrFe0.5Co0.5O3-y in alkaline solution was used to enhance its oxygen content. As a result of chemical titrations and Mössbauer spectroscopy studies, it is shown that the distribution of cobalt and iron oxidation states are heterogeneous, indicating that oxidation of cobalt cations requires higher oxidation potential than for the iron ones. Consequently, the random distribution of Co4+ and Fe4+ often considered is wrong. When oxygen content increases, a paramagnetic to ferromagnetic transition is evidenced at 305 K for SrFe4+0.50Co3+0.34Co4+0.16O2.83±0.02. The study of its magnetocaloric effect was performed, and special attention was paid to the air aging effect. Despite the small amount of oxygen release that slightly shifts toward a lower temperature of the ferromagnetic transition, the remarkable stability of its refrigerant capacity is highlighted. It suggests that a high content of Co4+ oxidation state is kept.