Qureshi Navid, Ressouche Eric, Mukhin Alexander, Gospodinov Marin, Skumryev Vassil
Institut Laue-Langevin, 71 Avenue des Martyrs, 38042 Grenoble Cedex 9, France.
Université Grenoble Alpes, CEA, IRIG, MEM, MDN, F-38000 Grenoble, France.
Sci Adv. 2020 Feb 14;6(7):eaay7661. doi: 10.1126/sciadv.aay7661. eCollection 2020 Feb.
CuO is the only known binary multiferroic compound, and due to its high transition temperature into the multiferroic state, it has been extensively studied. In comparison to other prototype multiferroics, the nature and even the existence of the high-temperature incommensurate paraelectric phase (AF3) were strongly debated-both experimentally and theoretically-since it is stable for only a few tenths of a kelvin just below the Néel temperature. Until now, there is no proof by neutron diffraction techniques owing to its very small ordered Cu magnetic moment. Here, we demonstrate the potential of spherical neutron polarimetry, first, in detecting magnetic structure changes, which are not or weakly manifest in the peak intensity and, second, in deducing the spin arrangement of the so far hypothetic AF3 phase. Our findings suggest two coexisting spin density waves emerging from an accidental degeneracy of the respective states implying a delicate energy balance in the spin Hamiltonian.
氧化铜是唯一已知的二元多铁性化合物，由于其转变为多铁性状态的温度较高，因此受到了广泛研究。与其他典型的多铁性材料相比，高温非公度顺电相（AF3）的性质甚至其存在性在实验和理论上都存在激烈争论，因为它仅在略低于尼尔温度的几十分之一开尔文范围内稳定。到目前为止，由于其有序铜磁矩非常小，尚无通过中子衍射技术获得的证据。在此，我们展示了球形中子极化imetry的潜力，首先是检测在峰强度中不明显或微弱显现的磁结构变化，其次是推断迄今为止假设的AF3相的自旋排列。我们的研究结果表明，两个共存的自旋密度波源自各自状态的偶然简并，这意味着自旋哈密顿量中存在微妙的能量平衡。
