Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Straße 40, 01187 Dresden, Germany.
Institut Laue-Langevin, 71 Avenue des Martyrs, F-38042 Grenoble Cedex 9, France.
Sci Adv. 2016 May 27;2(5):e1600353. doi: 10.1126/sciadv.1600353. eCollection 2016 May.
Magnetoelectric multiferroics have attracted enormous attention in the past years because of their high potential for applications in electronic devices, which arises from the intrinsic coupling between magnetic and ferroelectric ordering parameters. The initial finding in TbMnO3 has triggered the search for other multiferroics with higher ordering temperatures and strong magnetoelectric coupling for applications. To date, spin-driven multiferroicity is found mainly in oxides, as well as in a few halogenides. We report multiferroic properties for synthetic melanothallite Cu2OCl2, which is the first discovery of multiferroicity in a transition metal oxyhalide. Measurements of pyrocurrent and the dielectric constant in Cu2OCl2 reveal ferroelectricity below the Néel temperature of ~70 K. Thus, melanothallite belongs to a new class of multiferroic materials with an exceptionally high critical temperature. Powder neutron diffraction measurements reveal an incommensurate magnetic structure below T N, and all magnetic reflections can be indexed with a propagation vector [0.827(7), 0, 0], thus discarding the claimed pyrochlore-like "all-in-all-out" spin structure for Cu2OCl2, and indicating that this transition metal oxyhalide is, indeed, a spin-induced multiferroic material.
磁电多铁性材料在过去几年中引起了极大的关注，因为它们在电子设备中的应用潜力很大，这是由于磁有序参数和铁电有序参数之间的固有耦合。在 TbMnO3 中的最初发现引发了对其他具有更高有序温度和强磁电耦合的多铁性材料的研究。迄今为止，自旋驱动的多铁性主要存在于氧化物中，以及少数卤化物中。我们报告了合成的黑钨铜矿 Cu2OCl2 的多铁性，这是在过渡金属卤氧化物中首次发现的多铁性。在 Cu2OCl2 中测量的热电流和介电常数表明在约 70 K 的奈尔温度以下存在铁电性。因此，黑钨铜矿属于具有异常高临界温度的新型多铁性材料。粉末中子衍射测量表明在 TN 以下存在非共线磁结构，并且所有磁反射都可以用传播矢量 [0.827(7)，0，0] 索引，从而排除了对 Cu2OCl2 中所声称的钙钛矿样“全内全出”自旋结构的要求，并表明这种过渡金属卤氧化物确实是一种由自旋诱导的多铁性材料。
