High-temperature ferroelectric order and magnetoelectric coupling driven by the magnetic field cooling effect in R2BaCuO5(R=Er,Dy,Sm)

The high-temperature ferroelectric order and a remarkable magnetoelectric effect driven by the magnetic field cooling are reported in ${R}₂{\mathrm{BaCuO}}₅\phantom{\rule{4pt}{0ex}}(R$ = Er, Dy, Sm) series. The ferroelectric (FE) orders are observed at much higher temperatures than their magnetic orders for all three members. The value of FE Curie temperature $({T}_{\mathrm{FE}})$ is considerably high as $\ensuremath{\sim}235$ K with the polarization value $(P)$ of $\ensuremath{\sim}1410\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{C}/{\mathrm{m}}²$ for a 4 kV/cm poling field in the case of ${\mathrm{Er}}₂{\mathrm{BaCuO}}₅$, whereas the values of ${T}_{\mathrm{FE}}$ and $P$ are also promising as $\ensuremath{\sim}232$ and $\ensuremath{\sim}992\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{C}/{\mathrm{m}}²$ for ${\mathrm{Dy}}₂{\mathrm{BaCuO}}₅$, and $\ensuremath{\sim}184$ K and $\ensuremath{\sim}980\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{C}/{\mathrm{m}}²$ for ${\mathrm{Sm}}₂{\mathrm{BaCuO}}₅$. The synchrotron diffraction studies of ${\mathrm{Dy}}₂{\mathrm{BaCuO}}₅$ confirm a structural transition at ${T}_{\mathrm{FE}}$ to a polar $Pna{2}₁$ structure, which correlates the FE order. An unusual magnetoelectric coupling is observed below the $R$ order for Er and Dy compounds and below the Cu order for Sm compound, when the pyroelectric current is recorded only with the magnetic field both in heating and cooling cycles, i.e., the typical magnetic field cooled effect. The magnetic field cooled effect driven emergence of polarization is ferroelectric in nature, as it reverses due to the opposite poling field.