Switchable and Nonswitchable Polarization in Doubly Ordered Perovskites NaLnCoWO6 (Ln = Er, Tm, Yb, and Lu)

We report the multiferroic properties of doubly ordered perovskites NaLnCoWO6 (Ln = Er, Tm, Yb, and Lu) and NaLuMnWO6 synthesized under high-pressure (4.5 GPa) and high-temperature (1000 °C) conditions. Analysis of the powder X-ray diffraction data reveals that these compounds crystallize in the polar monoclinic (P21) structure. These compounds are derived from the ABO3 perovskite structure, where A-site cations (Na and Ln) exhibit layer ordering and B-site ions (M = Co or Mn and W) undergo commonly observed rock-salt ordering accompanied by a–a–c+ octahedral tilting. All these materials, characterized by magnetic and dielectric measurements, reveal antiferromagnetic ordering (TN ∼ 6–8 K) accompanied by a dielectric anomaly. Furthermore, pyroelectrical current measurements show a nonswitchable polarization below TN for NaLnCoWO6 (Ln = Er, Tm, and Yb) and NaLuMnWO6. In contrast, the polarization can be switched in NaLuCoWO6 by changing the direction of the electric field (E) indicating the ferroelectric nature of this compound. The appearance of polarization below the magnetic ordering temperature (TN) confirmed the magnetoelectric coupling of these compounds.