Structural transformations and magnetic properties of Bi 1– x Ln x FeO 3 (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 Bi 1– x La x FeO 3 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 Pnma 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 Bi 1– x Nd x FeO 3 system. In the case of Bi 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 Pnma and Imma phases that do not allow conventional ferroelectricity. The ferroelectric R3c phase exhibits metamagnetic behavior due to transition from an incommensurately modulated antiferromagnetic state to a weak ferromagnetic state. Substitution of Bi 3+ with Ln 3+ leads to a strong decrease of external magnetic field inducing a metamagnetic transition. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)