Magnetic, magnetoelectric, magnetodielectric and magnetoresistance studies on CuO doped Sr₂Bi₄Ti₅O₁₈ lead free ferroelectric ceramics

As an effort to develop new multiferroic materials at room temperature, we have interstitially doped (x mol %) low dimensional CuO with strong superexchange interactions into lead-free ferroelectric Sr₂Bi₄Ti₅O₁₈ (SBT) ceramics. Upon increase of CuO doping concentration (x = 0, 0.25, 0.5, 0.75 & 1) in SBT + x mol % compound a small and noticeable, but not appreciable, SrTiO₃ secondary phase segregates in the SBT. Thus, CuO doping induces SrTiO₃ phase and induced volume increase with "x". The undoped SBT shows weak magnetization (μemu/g) at room temperature and magnetization enhances three-fold (memu/g) with CuO doping in SBT. The thermomagnetic studies of all the samples under zero field cooled, and field cooled modes show typical paramagnetic nature below room temperature and no spin glass-like phases. The Curie–Weiss law analysis suggest that antiferromagnetic interactions are predominant at low temperature in all the CuO doped samples except x = 0.75, which show ferromagnetic interactions. In the direct test for magnetoelectric properties, all the samples show similar magnetoelectric coupling coefficient (α). Among all, the x = 1 sample shows relatively low "α" indicating the magnetoelectric coupling weakens at high CuO concentration. Further, in an indirect test (magnetocapacitance) for magnetoelectric coupling shows similar to magnetoelectric behavior. As reported, the magnetocapacitance may originate from magnetoresistance (MR) and Maxwell–Wagner polarization effect. Our low field MR study on all samples suggests that large magnetocapacitance in x = 1 sample is not due to the extrinsic phenomenon. However further studies are essential to confirm our present inference. - Highlights: • Sr₂Bi₄Ti₅O₁₈ + x mol% CuO ceramics were prepared by solid state reaction method. • The highest magnetization value of 5.5 memu/g was observed at room temperature for x = 0.75 sample. • Curie–Weiss law analysis suggests that x = 0.75 sample exhibit ferromagnetic behavior at low temperature. • Magnetoelectric coupling was attributed in the prepared samples due to the coexistence of magnetic and electric phases. • The highest room temperature negative magnetoresistance value of ∼4% at 0.85 T was observed for x = 0 and 0.75 samples.