Oxygen excess in the “114” cobaltite hexagonal structure: The ferrimagnet CaBaCo4O7.50

The study of the oxidation of the “114” orthorhombic cobaltite CaBaCo4O7, using first electrochemistry and then soft chemistry based on oxidation by NaClO, has allowed a new phase, CaBaCo4O7.50, to be prepared topotactically. The structural study of this phase shows that its hexagonal structure, closely related to that of orthorhombic CaBaCo4O7, is curiously similar to that of the members of the LnBaCo4O7 series, in spite of its excess oxygen. Its magnetic study shows that this phase, like CaBaCo4O7, is ferrimagnetic with the same TC (60 K), but differently exhibits an unusual magnetic hysteresis. This exceptional behavior of CaBaCo4O7 with respect to oxidation as well as the magnetic properties of CaBaCo4O7.50 is interpreted in terms of the presence of defects due to oxidation.