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

Abstract

We report the multiferroic properties of doubly ordered perovskites NaLnCoWO 6 (Ln = Er, Tm, Yb, and Lu) and NaLuMnWO 6 synthesized under high-pressure (4.5 GPa) and high-temperature (1000 °C) conditions. Analysis of the powder Xray diffraction data reveals that these compounds crystallize in the polar monoclinic (P2 1 ) structure. These compounds are derived from the ABO 3 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 (T N ∼ 6−8 K) accompanied by a dielectric anomaly. Furthermore, pyroelectrical current measurements show a nonswitchable polarization below T N for NaLnCoWO 6 (Ln = Er, Tm, and Yb) and NaLuMnWO 6 . In contrast, the polarization can be switched in NaLuCoWO 6 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 (T N ) confirmed the magnetoelectric coupling of these compounds.

Insights into Cation Ordering of Double Perovskite Oxides from Machine Learning and Causal Relations

“…The rock-salt ordering of B-site cations helps to keep highly charged cations farther apart from each other enabling ordering in AA'BB'O 6 . For NaLnMWO 6 (M = Mn, Co, Ni, and Ln = La–Lu), stablized A-site layer with B-site rock-salt ordering has been observed. − …”

“…(b)­Additionally, we have constructed another validation set based on selected compounds for which experimental evidence of A-site cation ordering is available. − , We have chosen a total of 17 compounds, NaLaInNbO 6 , NaLaInTaO 6 , NaYMnWO 6 , NaYNiWO 6 , NaDyNiWO 6 , NaHoNiWO 6 , NaLaNiWO 6 , NaPrNiWO 6 , NaNdNiWO 6 , NaSmNiWO 6 , NaEuNiWO 6 , NaGdNiWO 6 , NaTbNiWO 6 , NaErCoWO 6 , NaTmCoWO 6 , NaYbCoWO 6 , and NaLuCoWO 6 . All of these compounds crystallize into noncentrosymmetric space groups such as P 2 1 and P 42 1 2 for which (a – a – c + ) distortion is possible.…”

“…At its current stage, these data on different A-site cation ordering arrangements are not available in literature. Most of the experimental observations have reported compounds where A-site layered ordering is favorable. − Thus, our computational data can become a good addition for further explorations. The study is intended to aid into interpretability as well as discovery of cause–effect relationships (going beyond the standard practices of ML to uncover structure–property relationships) between features representing cation ordering in double perovskites.…”

“…In this case, a cutoff energy difference of −32 meV is set. This choice is driven by the fact that double perovskite systems most likely exhibit clear layered ordering as validated by experimental observations. − More compounds may show clear layered ordered phases if the cutoff energy is lowered and vice versa. We specify the cutoff at −32 meV for the following reasons.…”

Pressure Dependence of Structural Behavior and Electronic Properties in Double Perovskite Ba2SmSbO6

“…12,13 A 2 B′B″O 6 with rare-earth B′ and B″ cations attracts widespread attention, due to geometric magnetic frustration 14 and high-quality superconducting thick films. 15 Recently, reports of double perovskites continue to exhibit significant progress in magnetic order 16,17 and photoluminescence properties. 41,42 For example, the antiferromagnetic order of Ni 2+ ion moments is determined by Ln = La, Pr, Nd, Sm, Eu, Gd, and Tb in double perovskite NaLnNiWO 6 in the range of 23−30 K. 16 The ferrimagnetic order of Er 2 CoMnO 6 stems from the longrange order of Er 3+ moments below 10 K. 17 Furthermore, when Eu 3+ ions are doped into the Sr 2 YTaO 6 41 and La 2 CaSnO 6 , 42 the phosphors emit high purity red light.…”