Multiferroic materials, in which electric polarization is induced by magnetic phase transitions driven by temperature or applied magnetic fields, have been extensively studied since their discovery in the early 21st century. From an applications standpoint, identifying compounds that exhibit large changes in polarization (ΔP ) is crucial. However, materials showing ΔP larger than 10 mC/m² have been scarce.

　The polar ferrimagnet CaBaCo₄O₇ is known to exhibit the largest ΔP  among multiferroic materials discovered to date. This large magnetoelectric (ME) response accompanies the transition from an antiferromagnetic phase (stable between 69 and 62 K) to a ferrimagnetic phase that becomes stable at lower temperatures, and it can be triggered not only by temperature changes but also by applied magnetic fields. We demonstrate that substituting as little as 2.5% Ni for Co in CaBaCo₄O₇ significanly enhances the ME effect [A]. Specifically, (i) the magnitude of ΔP  increases from 8 mC/m² to more than 10 mC/m², and (ii) the temperature window over which a giant field-induced ME effect appears expands by more than an order of magnitude. These results indicate that chemical substitution of existing multiferroics is a powerful route to amplifying magnetoelectric responses.

References

[A] M. Gen et al., Phys. Rev. B 105, 214412 (2022). (Original paper [14])