Exploring new members of magnetoelectric materials in CuO–CuCl₂–SeO₂ system

Materials containing Cu²⁺ ions with quantum spin S = 1/2 and oxyhalide groups are an intriguing avenue for exploring quantum-magnetic phenomena. The CuO–CuCl₂–SeO₂ system has captured significant attention within the research community because of its potential to unveil new magnetic phases and their corresponding properties. Over the past decade, numerous researchers have investigated the unique physical properties of various compounds in this system and their structural correlations. In this study, we investigate the structural, magnetic, and magnetoelectric properties of three compounds: Cu₃(SeO₃)₂Cl₂, Cu₅(SeO₃)₄Cl₂, and Cu₇O₂(SeO₃)₂Cl₆. The detailed magnetic and dielectric properties of Cu₃(SeO₃)₂Cl₂ indicate antiferromagnetic ordering at T_N = 38 K with a dielectric anomaly independent of the magnetic origin, whereas Cu₅(SeO₃)₄Cl₂ shows finite magnetoelectric coupling near T_N = 42 K. More importantly, we successfully synthesized the Nicksobolevite Cu₇O₂(SeO₃)₂Cl₆ compound, which is a more complex structure, from the CuO–CuCl₂–SeO₂ system. Interestingly, Cu₇O₂(SeO₃)₂Cl₆ and Cu²⁺ ions formed a spin-frustrated lattice with a cluster of corners sharing Cu²⁺ tetrahedra connected by eight Cu atoms running along the crystallographic b-axis. Complex magnetism with canted antiferromagnetic ordering at T_N = 11 K was consistent with the finite hysteresis in the M-H curve, specific heat C_p, and dielectric anomaly, indicative of strong magnetoelectric coupling. Additionally, systematic changes in the magneto-dielectric behavior after magnetoelectric poling revealed resilient coupling between the magnetic and electric domains. Our study provides insights into the unique properties of these compounds and offers a detailed comparison with other multiferroic compounds in the CuO–CuCl₂–SeO₂ system.