Enhancing the high-TC spiral multiferroic phase by uniaxial strain in YBaCuFeO5

YBaCuFeO5 displays magnetism-driven ferroelectricity (FE) at unexpectedly high temperatures. Electrical polarization develops associated to a spiral magnetic order, whose ordering temperature can be increased by more than 180 K (beyond RT) by manipulating the Cu/Fe chemical disorder in powder samples (A. Romaguera et al., Phys. Rev. Research (2022)). However, single crystals present too much Cu/Fe order and lower spiral transition temperatures due to its fabrication method (floating-zone).
We aim to apply uniaxial stress to single crystals of YBaCuFeO5 with Tspi=195 K in normal conditions. This is the highest spiral temperature reported so far in single crystals. Chemical substitutions results (in powders) that favor the compression of the FeCuO9 bipyramids and the theoretical models (Science Adv. 4, eaau6386 (2018)) indicate that compressing the thickness (dt) of the bipyramidal a-b layer raises magnetic frustration and the thermal stability of the spiral order. We aim to apply compressive uniaxial stress along-c to drive the incommensurate spiral phase to normal working temperatures, above 300 K.