Microstructure and Magnetic Properties of Metastable RFeO_3 (R: Rare-earth element) Formed from Undercooled Melt

摘要

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 (P_(O_2)) on the microstructure and physical properties of rare-earth orthoferrites RFeO_3 (where R = Rare-earth element) in the P_(O_2) ranges from 10~5 to 10~(-1) Pa. The micro-structure of the as-solidified samples changed into ortho-rhombic RFeO_3 (o-RFeO_3), metastable hexagonal RFeO_3 (h-RFeO_3), and Fe -containing RFe_2O_4 and a new metastable R_3Fe_2O_7 phases with decreasing P_(O_2). The effect of P_(O_2) 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 P_(O_2) due to the formation of metastable and magnetic phases such as Fe_3O_4 and Fe.