  Large magnetoelectric response in thin films is highly desired for
high-throughput and high-density microelectronic applications. However, the d0
rule in single-phase compounds usually results in a weak interaction between
ferroelectric and magnetic orders; the magnetoelectric coupling via elastic
resonance in composites restricts their thin-film integration in broadband.
Here, we effectuate a concurrence of ferroelectric-like and antiferromagnetic
phase transitions in Sr2IrO4/SrTiO3 superlattices by artificial design
periodically non-equivalent interfaces, where a maximum magnetoelectric
coefficient of ~980 mV cm-1 Oe-1 can be measured. Evidenced by synchrotron
X-ray absorption and electron energy loss spectroscopies, a lopsided electron
occupation occurs at the interfacial Ti ions. From perturbative calculations
and numerical results, a strong coupling of antiferromagnetism and asymmetric
electron occupation mediated by spin-orbit interaction leads to a large bulk
magnetoelectric response. This atomic tailoring of the quantum order parameters
in 3d and 5d oxides provides an alternative pathway towards strong
magnetoelectric effects with thin-film integrations.
