有限海森堡自旋链中的奇偶效应
Even-odd effects in finite Heisenberg spin chains
摘要：
磁性超晶格和纳米线可以被描述为有限长度N的海森堡自旋链，其中N是磁性单元（分别是膜或原子）的数量。我们研究反铁磁耦合的自旋，也耦合到外部场H（超晶格）或铁磁衬底（纳米线）。该模型是通过一个二维地图，允许快速和可靠的数值计算进行分析。开链和闭链对于偶数和奇数N都有不同的性质（奇偶效应）。具有奇数N的开链是已知的[S.Lounis等人，物理修订版信函101，107204（2008）]，以具有亚铁磁状态的小N和非共线状态的大N。本文用解析方法求出了过渡长度N_c。最后，我们表明，封闭链安排自己在均匀的体自旋翻转状态为偶数N和非均匀状态为奇数N。
英文摘要：
Magnetic superlattices and nanowires may be described as Heisenberg spin chains of finite length N, where N is the number of magnetic units (films or atoms, respectively). We study antiferromagnetically coupled spins which are also coupled to an external field H (superlattices) or to a ferromagnetic substrate (nanowires). The model is analyzed through a two-dimensional map which allows fast and reliable numerical calculations. Both open and closed chains have different properties for even and odd N (parity effect). Open chains with odd N are known [S.Lounis et al., Phys. Rev. Lett. 101, 107204 (2008)] to have a ferrimagnetic state for small N and a noncollinear state for large N. In the present paper, the transition length N_c is found analytically. Finally, we show that closed chains arrange themselves in the uniform bulk spin-flop state for even N and in nonuniform states for odd N.
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