Composition- and magnetic field-driven antiferromagnetic-weak ferromagnetic transition in Bi1−xCaxFe1−xTixO3 multiferroics

• Multiferroic properties of the Bi1−xCaxFe1−xTixO3 (x≤0.2) compounds were studied.
• The chemical replacement influences the stability of the cycloidal magnetic structure.
• The substitution results in the appearance of a weak-ferromagnetic polar state.

The investigation aims at assessing the influence of Ca2+/Ti4+ co-doping on the crystal structure and magnetic properties of the BiFeO3 multiferroic exhibiting cycloidal spin ordering in the polar phase. We show that increasing the content of the substituents results in reducing the stability range of the cycloidal antiferromagnetic structure in external magnetic field. Above the critical concentration corresponding to the composition with x=0.15, the cycloidal order is removed to enable the formation of a weak ferromagnetic state. The spontaneous magnetization characteristic of the doping-stabilized weak ferromagnetic phase is very close to the locked magnetization releasing upon the magnetic field-induced cycloidal ordering ↔ canted ordering transition observed in the compounds with x≤0.15. Since the doping-driven magnetic transformation is not accompanied by changes in the symmetry of the crystal lattice, the Ca2+/Ti4+ co-substitution provides a promising opportunity to combine switchable magnetization and polarization in a single phase.

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