Can the ferroelectric soft mode trigger an antiferromagnetic phase transition?

Type-II multiferroics, where spin interactions induce a ferroelectric polarization, are interesting for new device functionalities due to large magnetoelectric coupling. We report on a new type of multiferroicity in the quadruple-perovskite BiMn3Cr4O12, where an antiferromagnetic phase is induced by the structural change at the ferroelectric phase transition. The displacive nature of the ferroelectric phase transition at 125 K, with a crossover to an order-disorder mechanism, is evidenced by a polar soft phonon in the THz range and a central mode. Dielectric and pyroelectric studies show that the ferroelectric critical temperature corresponds to the previously reported Ne ' el temperature of the Cr3+ spins. An increase in ferroelectric polarization is observed below 48 K, coinciding with the Ne ' el temperature of the Mn3+ spins. This increase in polarization is attributed to an enhanced magnetoelectric coupling, as no change in the crystal symmetry below 48 K is detected from infrared and Raman spectra.

Automated summary

Type-II multiferroics show large magnetoelectric coupling and are promising for new device functionalities. We report a new multiferroic material, BiMn3Cr4O12, where an antiferromagnetic phase is induced by the structural change at the ferroelectric phase transition. Thermodynamic, dielectric, and pyroelectric studies reveal that the ferroelectric critical temperature corresponds to the Ne'el temperature of the Cr3+ spins, and an increase in ferroelectric polarization is observed below the Ne'el temperature of the Mn3+ spins.