Exploring magnetism and magnetoelectric properties in the green phase of R 2 BaCu O 5 ( R = Er , Eu, Y, Tm, and Lu): The role of 4 f − 3 d exchange coupling

We report a comprehensive investigation into the magnetic and magnetoelectric characteristics of green phase compounds R2BaCuO5 (R=Er, Eu, Y, Tm, and Lu) through an array of experimental techniques, including dc magnetization, specific heat, dielectric, pyrocurrent, and neutron diffraction measurements. Our study reveals that all these compounds exhibit antiferromagnetic ordering of Cu2+ ions in the range TN = 15–20 K. Specifically, magnetic ordering of Er3+ ions is observed at TN = 5.1 K. Intriguingly, independent ordering of Tm3+ ions is not observed. Furthermore, the isothermal magnetization curves for the Er compound confirm the metamagnetic transition at a critical magnetic field of Hc=0.9T, reaching a saturation magnetization value of 9µB/f.u. Notably, above Hc, this compound exhibits field-induced magnetoelectric states at TN, underscoring a pronounced magnetoelectric coupling. Conversely, the compounds with R=Eu, Y, Tm, and Lu do not display magnetoelectric coupling. The presence or absence of such coupling aligns with the magnetic symmetry derived from neutron diffraction. Our findings conclusively establish that 4f−3d exchange coupling is pivotal in enabling the magnetoelectric or multiferroic properties in these well-established green phase compounds. Consequently, our study underscores the rich and diverse magnetism and magnetoelectric properties exhibited by the green phase family, positioning them as equally intriguing as manganites in condensed matter physics.