Multiferroics are rare in nature due to the mutual exclusive origins of magnetism and ferroelectricity. The simultaneous coexistence of robust magnetism/ferroelectricity and strong magnetoelectric coupling in single multiferroics is hitherto unreported, which may also be attributed to their potential conflictions. In this paper, we show the first-principles evidence of such desired coexistence in ultrathin-layer CuCrS₂ and CuCrSe₂. The vertical ferroelectricity is neither induced by empty d-shell nor spin-driven, giving rise to an alternative possibility of resolving those intrinsic exclusions and contradictions. Compared with their bulk phases, the ferromagnetism in the thin-layer structures (2–6 layers) can be greatly stabilized due to the enhanced carrier density and orbital shifting by the vertical polarization, and the Curie temperatures of both ferromagnetism and ferroelectricity can be above room-temperature. Moreover, a considerable net magnetization can be reversed upon a ferroelectric switching, where the change in spin-resolved band structure also renders efficient “magnetic reading + electrical writing”. The thickness-different layers may even exhibit diversified types of magnetoelectric coupling, which both enriches the physics of multiferroics and facilitates their practical applications.

中文翻译：

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二维材料中的室温多铁性和多样化磁电耦合


由于磁性和铁电性的相互排斥的起源，多铁性在自然界中很少见。迄今为止，单一多铁性材料中强磁/铁电性和强磁电耦合的同时共存尚未见报道，这也可能归因于它们潜在的冲突。在本文中，我们展示了超薄层 CuCrS ₂和 CuCrSe ₂中这种理想共存的第一原理证据。垂直铁电性既不是由空 d 壳层引起的，也不是自旋驱动的，从而产生了解决这些内在排斥和矛盾的另一种可能性。与体相相比，由于垂直极化增强的载流子密度和轨道移位，薄层结构（2-6层）中的铁磁性可以大大稳定，并且铁磁性和铁电性的居里温度都可以高于室温。此外，在铁电切换时可以反转相当大的净磁化强度，其中自旋分辨能带结构的变化也实现了高效的“磁读取+电写入”。不同厚度的层甚至可以表现出多种类型的磁电耦合，这既丰富了多铁性材料的物理性质，又促进了其实际应用。