Enhancing the high-Tc spiral multiferroic phase by pressure in single-crystal YBaCuFeO5

YBaCuFeO5 (YBCFO) displays magnetism-driven ferroelectricity (FE) at unexpectedly high temperatures. The exceptional stability of the spiral magnetic order in YBCFO involves a non-conventional mechanism known as “spiral order by disorder”. Electrical polarization develops associated to the spiral (cycloidal) magnetic order, whose ordering temperature can be increased by more than 180 K (far 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). Chemical pressure results in powders and the theoretical models (Science Adv. 4, eaau6386 (2018)) indicate that compressing the thickness (dt) of the bipyramidal a-b layer in YBaCuFeO5 has a strong influence on the strength of the frustrated magnetic interactions and the stabilization of the spiral phase. We will apply this strategy and will study the influence of pressure on the spiral magnetic order of an YBaCuFeO5 single crystal with Tspi=195 K (previously characterized by polarized&unpolarized neutrons). This is the highest spiral temperature reported so far in single crystals. Our SXRD and Raman characterization under pressure also suggest a possible enhancement of the thermal stability of the spiral phase.