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High-pressure suppression of structural modulation waves in BaCoX2O7 multiferroic chain compounds

BaCoX2O7 (X= As, P) are built on magnetic chains in which strong aperiodic undulations arise from incommensurate structural modulations with large atomic displacive amplitudes, resulting in very unique multiferroic properties. High-pressure structural and vibrational properties have been investigated by synchrotron X-ray powder diffraction and Raman spectroscopy at room temperature and combined with density functional calculations. It highlights the disappearance of the structural modulation with the hydrostatic pressure during a first order transition. In addition to the atypical flattening of strongly waved chains, this is an important issue because the modulation mediates the multiferroicity in this family. This opens up questions about how the disappearance of this incommensurability changes the type of stabilized magnetic structure and how this affects the electrical properties.