Gambardella P, Dallmeyer A, Maiti K, Malagoli M C, Eberhardt W, Kern K, Carbone C
Institut de Physique des Nanostructures, EPF-Lausanne, CH-1015 Lausanne, Switzerland.
Nature. 2002 Mar 21;416(6878):301-4. doi: 10.1038/416301a.
Two-dimensional systems, such as ultrathin epitaxial films and superlattices, display magnetic properties distinct from bulk materials. A challenging aim of current research in magnetism is to explore structures of still lower dimensionality. As the dimensionality of a physical system is reduced, magnetic ordering tends to decrease as fluctuations become relatively more important. Spin lattice models predict that an infinite one-dimensional linear chain with short-range magnetic interactions spontaneously breaks up into segments with different orientation of the magnetization, thereby prohibiting long-range ferromagnetic order at a finite temperature. These models, however, do not take into account kinetic barriers to reaching equilibrium or interactions with the substrates that support the one-dimensional nanostructures. Here we demonstrate the existence of both short- and long-range ferromagnetic order for one-dimensional monatomic chains of Co constructed on a Pt substrate. We find evidence that the monatomic chains consist of thermally fluctuating segments of ferromagnetically coupled atoms which, below a threshold temperature, evolve into a ferromagnetic long-range-ordered state owing to the presence of anisotropy barriers. The Co chains are characterized by large localized orbital moments and correspondingly large magnetic anisotropy energies compared to two-dimensional films and bulk Co.
二维系统，如超薄外延膜和超晶格，展现出与块状材料不同的磁特性。当前磁学研究的一个具有挑战性的目标是探索维度更低的结构。随着物理系统维度的降低，由于涨落变得相对更重要，磁有序倾向于减弱。自旋晶格模型预测，具有短程磁相互作用的无限一维线性链会自发分裂成具有不同磁化方向的段，从而在有限温度下禁止长程铁磁序。然而，这些模型没有考虑达到平衡的动力学障碍或与支撑一维纳米结构的衬底的相互作用。在这里，我们证明了在铂衬底上构建的钴一维单原子链中同时存在短程和长程铁磁序。我们发现证据表明，单原子链由铁磁耦合原子的热涨落段组成，在低于阈值温度时，由于各向异性势垒的存在，这些段会演变成铁磁长程有序状态。与二维薄膜和块状钴相比，钴链的特征是具有大的局域轨道磁矩以及相应大的磁各向异性能量。
