Containerless Processing of Metastable Multiferroic Composite in R-Fe-O System (R: Rare-earth element)

Abstract

The hexagonal structure with a space group of P6(sub 3)cm has been known to be stable in the RMnO3 system (R: rare earth element) of the rare earth elements having smaller ionic radius. The hexagonal RMnO3 (h-RMnO3) has attracted great interest towards their wide applications in the field of electronic industry, because h-RMnO3 shows multiferroic properties such as ferroelectricity, ferromagnetism and ferroelasticity in the same phase. Nevertheless, the materials for practical applications remain undeveloped, because h-RMnO3 shows anti-ferromagnetism as well as low magnetic transformation temperature below 100 K. To solve this problem, we considered that a composite of a ferromagnetic phase and a ferroelectric phase is more realistic than a single-phase material. On the basis of this idea, we attempted to synthesize the multiferroic composite consisting of ferroelectric h-RFeO3 and ferromagnetic Fe3O4 by utilizing the containerless technique. The experimental result showed that it is possible to exhibit a fine composite structure when h-LuFeO3 and Fe3O4 are equimolar amounts. However, the orthorhombic phase (o-RFeO3) as well as h-RFeO3 was observed in the samples in which the mole-fraction of Fe3O4 was increased. The reason for forming the o-RFeO3 phase is attributed to the decrease of the driving force for forming a metastable phase due to the fact that the solute atom or molecule is redistributed at the solid-liquid interface of the growing crystal.