abstract
Neutron powder diffraction measurements on the 35 % La-substituted Bi1-xLaxFe0.5Sc0.5O3-composition revealed that the samples obtained under high-pressure (6 GPa) and high-temperature (1500 K) conditions crystalize into a distorted perovskite structure with the orthorhombic Pnma symmetry and the unit cell para-meters: a(0) = 5.6745(2) angstrom, b(0) = 7.9834(3) angstrom and c(0) = 5.6310(2) angstrom. A long-range magnetic ordering takes place below 220 K and implies a G-type magnetic structure with the moments 4.10(4)mu(B) per Fe aligned predominately along the orthorhombic c-axis. The space group representation theory using the orthorhombic symmetry yields four bi-linear coupling schemes for the magnetic order parameters imposed by antisymmetric exchange interactions. The couplings are analysed based on symmetry adapted distortion modes defined in respect of the undistorted cubic perovskite structure. The approach allows a quantitative estimation of the coupling strength. It is shown that the experimentally found spin configuration combines the magnetic order parameters coupled by the atomic displacement modes with the largest amplitudes. The results indicate that the antisymmetric exchange is the dominant anisotropic term which fully controls the direction of the Fe3+ spins in the distorted perovskite lattice.
keywords
WEAK FERROMAGNETISM; THERMODYNAMIC THEORY; PEROVSKITES
subject category
Crystallography
authors
Khalyavin, DD; Salak, AN; Manuel, P; Olekhnovich, NM; Pushkarev, AV; Radysh, YV; Fedorchenko, AV; Fertman, EL; Desnenko, VA; Ferreira, MGS
our authors
Andrei Salak
Principal Researcher
Mário Guerreiro Silva Ferreira
Retired Professoracknowledgements
This work was supported by project TUMOCS. This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 645660.