Room temperature multiferroicity and magnetoelectric coupling in Ca/Mn-modified BaTiO₃

Materials with magnetoelectric coupling (MEC) between ferroic orders at room temperature are an emerging field in modern technology and physics. BaTiO₃ is a robust ferroelectric material in which several types of doping have led to MEC. Ca- and Mn-modified BaTiO₃ has been studied with a series of Ba_(1−x)Ca_(x)Ti_(1−y)Mn_(y)O₃ (x = y = 0, 0.03, 0.06, and 0.09) substitutions; here, MEC was only observed when x = 0.03. A mixed phase of tetragonal P4mm and hexagonal P6₃/mmc space groups of BaTiO₃ are observed in the substituted samples, with nominal contribution of the hexagonal phase when x = 0.03. Substitution in BaTiO₃ as described above results in structural modifications with reduced Ti-O-Ti bond angles and a large number of defects in the tetragonal phase, leading to weak ferromagnetism. Valence state study using XPS and XANES reveals an enhanced proportion of Mn³⁺ ions in the sample, which supports pseudo Jahn-Teller distortion, thereby supporting ferroelectricity and inducing weak magnetic ordering due to short range magnetic exchange interactions and bound magnetic polarons in the tetragonal phase at x = 0.03. The simultaneous existence of ferroelectricity and ferromagnetism in the tetragonal phase induces magnetoelectric coupling in this material. Furthermore, the linear response of polarization with an applied AC magnetic field indicates direct MEC. A magnetoelectric coupling coefficient (α_ME) of ∼0.704 mV cm⁻¹ Oe⁻¹ was obtained for a DC magnetic field of 800 Oe and an AC field of 40 Oe. This MEC was not observed for Ca and Mn substitutions in BaTiO₃ at x = 0.06 or 0.09, which emphasizes the sensitivity of structural properties towards substitution.