We report observation of surface-defect-induced room-temperature multiferroicity—surface ferromagnetism ($M_S$ at 50 kOe $\approx 0.005$ emu/g), ferroelectricity ($P_R\approx 2\mathrm{nC}/{\mathrm{cm}}^2$), and significantly large magnetoelectric coupling (decrease in $P_R$ by $\approx 80\%$ under $\approx 15$ kOe field)—in nanorods (diameter $\approx 100$ nm) of double perovskite ${\mathrm{Y}}_2{\mathrm{NiMnO}}_6$ compound. In bulk form, this system exhibits multiferroicity only below its magnetic transition temperature $T_N\approx$ 70 K. On the other hand, the oxygen vacancies, formed at the surface region (thickness $\approx 10$ nm) of the nanorods, yield long-range magnetic order as well as ferroelectricity via Dzyloshinskii-Moriya exchange coupling interactions with strong Rashba spin-orbit coupling. Sharp drop in $P_R$ under magnetic field indicates strong cross coupling between magnetism and ferroelectricity as well. Observation of room-temperature magnetoelectric coupling in nanoscale for a compound which, in bulk form, exhibits multiferroicity only below 70 K underscores an alternative pathway for inducing magnetoelectric multiferroicity via surface defects and, thus, in line with magnetoelectric property observed, for example, in domain walls or boundaries or interfaces of heteroepitaxially grown thin films which do not exhibit such features in their bulk.

中文翻译：

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Y2NiMnO6纳米棒的室温表面多铁性

我们报告了对表面缺陷引起的室温多铁性——表面铁磁性的观察。${米}_{\mathrm{小号}}$在 50 千瓦时$\approx 0.005$emu/g), 铁电性 (${磷}_R\approx 2\mathrm{数控}/{\mathrm{厘米}}^2$），以及显着大的磁电耦合（减少在${磷}_R$经过$\approx 80\%$在下面$\approx 15$kOe 场）——以纳米棒为单位（直径$\approx 100$nm) 的双钙钛矿${\mathrm{是}}_2{\mathrm{镍锰}}_6$化合物。在散装形式中，该系统仅在其磁转变温度以下表现出多铁性${吨}_{ñ}\approx$70 K。另一方面，在表面区域形成的氧空位（厚度$\approx 10$nm）的纳米棒，通过 Dzyloshinskii-Moriya 交换耦合相互作用与强 Rashba 自旋轨道耦合产生长程磁序和铁电性。急剧下降${磷}_R$在磁场下也表明磁性和铁电之间的强交叉耦合。观察到一种化合物在纳米尺度上的室温磁电耦合，该化合物以块状形式仅在 70 K 以下表现出多铁性，强调了通过表面缺陷诱导磁电多铁性的替代途径，因此与观察到的磁电特性一致，例如，在异质外延生长薄膜的畴壁或边界或界面，它们在其体积中不表现出此类特征。