Evolution of magnetic and dielectric properties in Sr-substituted high-temperature multiferroic YBaCuFeO₅

We report the evolution of structural, magnetic and dielectric properties due to the partial substitution of Ba by Sr in the high-temperature multiferroic YBaCuFeO₅. This compound exhibits ferroelectric and antiferromagnetic transitions around 200 K and these two phenomena are presumed to be coupled with each other. Our studies on magnetic and dielectric properties of the ${\text{YBa}}_{1-x}{\text{Sr}}_x{\text{CuFeO}}_5$ ($x=0.0$, 0.25 and 0.5) show that the substitution of Sr shifts the magnetic transition towards higher temperature, whereas the dielectric transition to lower temperature. These results indicate that the magnetic and dielectric transitions might not be interrelated in the Sr-substituted YBaCuFeO₅. The nature of magnetodielectric coupling changes across the series with the presence of higher-order coupling terms. Additionally, in these compounds glassy dynamics of electric dipoles is observed at low temperatures. (letter)