title: Structural defects as a factor controlling the magnetic properties of pure and Ti-doped Bi(1-x)Ca(x)FeO(3-x/2) multiferroics.
abstract: Recognition of the factors that may significantly affect the multiferroic properties of BiFeO3-based perovskites remains one of the most challenging tasks in condensed matter physics. To reveal the reasons behind the doping-driven instability of the cycloidal antiferromagnetic order in the polar phase of Bi(1-x)Ca(x)FeO(3-x/2), synthesis and investigation of the crystal structure, microstructure, local ferroelectric and magnetic properties of the ceramic samples of Bi0.9Ca0.1Fe(1-x)Ti(x)O(3-δ) (x  =  0.05, 0.1, 0.15) have been carried out. The compounds possess a rhombohedral structure (space group R3c). The compositional dependence of unit cell volume in this series can be interpreted as suggesting the doping-induced elimination of anion vacancies at x  ⩽  0.1 and the formation of cation vacancies at x  >  0.1. The filling of oxygen vacancies suppresses a weak ferromagnetic contribution characteristic of the parent Bi0.9Ca0.1FeO2.95. The appearance of cation vacancies restores the weak ferromagnetic phase. The key role of lattice defects in the magnetic behavior of Ca-doped BiFeO3 has been confirmed by the observation of a correlation between the magnetic properties and the morphology/ferroelectric domain structure of the Bi0.9Ca0.1Fe(1-x)Ti(x)O(3-δ) ceramics.
authors.affiliation: CFisUC, Department of Physics, University of Coimbra, P-3004-516 Coimbra, Portugal.
authors.forename: V A
authors.initials: VA
authors.lastname: Khomchenko
authors.forename: J A
authors.initials: JA
authors.lastname: Paixão