Microstructure and magnetic properties of metastable RFeO₃ (R: Rare-earth element) formed from undercooled melt

Containerless levitation technique, where the undercooling can be treated as one of the major thermodynamic parameters, was used to study the influence of oxygen partial pressure (PO2) on the microstructure and physical properties of rare-earth orthoferrites RFeO₃ (where R = Rare-earth element) in the PO2 ranges from 10⁵ to 10^-1 Pa. The microstructure of the as-solidified samples changed into orthorhombic RFeO₃ (o-RFeO ₃), metastable hexagonal RFeO₃ (h-RFeO₃), and Fe²⁺-containing RFe₂O₄ and a new metastable R₃Fe₂O₇ phases with decreasing PO2. The effect of PO2 on the magnetic properties was indicated as that the saturation magnetization gradually increased for R = La to Yb and decreased for R = Lu with decreasing PO2 due to the formation of metastable and magnetic phases such as Fe₃O₄ and Fe.