Structural transformations and magnetic properties of Bi1-xLnxFeO3 (Ln = La, Nd, Eu) multiferroics

Crystal structures of Bi(1-x)Ln(x)FeO(3) systems (Ln = La, Nd, Eu) are studied using X-ray and neutron diffraction, magnetization measurements as well as electron microscopy. It was shown that the unit cell of the Bi1-xLaxFeO3 system is described with the R3c space group in the concentration interval 0 < x < 0.15, with the space group Imma (0.4 < x < 0.5) and with the Puma at x > 0.5. The mixed-phase state was observed in the range 0.15 < x < 0.4 independent of synthesis conditions. A similar sequence of the phase transformations was observed for Bi1-xNdxFeO3 system, In the case of qBi(1-x)Eu(x)FeO(3) series the unit cell is rhombohedral (R3c) at x 0.08 and orthorhombic (Pnma) at x > 0.20, whereas no evidence for Imma phase was found. The magnetization study has revealed the spontaneous magnetization to be associated with Prima and Imma phases that do not allow conventional ferroelectricity, The ferroelectric R3c phase exhibits meta-magnetic behavior due to transition from an incommensurately modulated antiferromagnetic state to a weak ferromagnetic state. Substitution of Bi3+ with Ln(3+) leads to a strong decrease of external magnetic field inducing a metamagnetic transition. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim