A Multiferroic Morphotropic Phase Boundary.
basic_science · Level V
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- Record sourced from PubMed, PMID 42700399.
- Also identified by DOI 10.1002/adma.74920.
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Abstract
Bismuth ferrite (BiFeO<sub>3</sub>) thin films possess large ferroelectric polarization and antiferromagnetic order, yet their magnetoelectric coupling is limited by weak intrinsic magnetization. Here, a multiferroic morphotropic phase boundary (MPB) is demonstrated wherein the crystal structure, polarization, and magnetic order simultaneously evolve across a chemically induced phase boundary in strain-engineered (1-x)BiFeO<sub>3</sub>-(x)BaTiO<sub>3</sub> thin films. Between 0.1 < x < 0.2, the crystal structure evolves from a monoclinic phase to a newly stabilized tetragonal phase through an intermediate mixed-phase region. This structural transition is accompanied by concurrent changes in magnetic order, resulting in dramatically enhanced functional responses as compared with those of BiFeO<sub>3</sub>. Specifically, films with x = 0.2 exhibit larger electromechanical strains (≈ 0.3%, about three-times larger than BiFeO<sub>3</sub>) and a significantly enhanced magnetoelectric-coupling coefficient (α<sub>ME</sub> ≈ 416 mV cm<sup>-1</sup> Oe<sup>-1</sup>, nearly 1000- and 19-times larger than bulk and thin-film BiFeO<sub>3</sub>, respectively). These enhancements diminish beyond the MPB (x > 0.2) and arise from polarization rotation and evolving spin configurations driven by the near degeneracy of competing ferroic states at the multiferroic MPB. These results establish a rare multiferroic MPB where both the polar and magnetic order evolve simultaneously, providing a promising strategy for designing materials with strongly coupled ferroic order parameters.