Departamento de Física de Materiales UPV/EHU, 20018 Donostia-San Sebastián, Spain.
Donostia International Physics Center (DIPC), 20018 Donostia-San Sebastián, Spain.
Molecules. 2018 Apr 20;23(4):964. doi: 10.3390/molecules23040964.
The magnetic anisotropy and exchange coupling between spins localized at the positions of 3d transition metal atoms forming two-dimensional metal⁻organic coordination networks (MOCNs) grown on a Au(111) metal surface are studied. In particular, we consider MOCNs made of Ni or Mn metal centers linked by 7,7,8,8-tetracyanoquinodimethane (TCNQ) organic ligands, which form rectangular networks with 1:1 stoichiometry. Based on the analysis of X-ray magnetic circular dichroism (XMCD) data taken at T = 2.5 K, we find that Ni atoms in the Ni⁻TCNQ MOCNs are coupled ferromagnetically and do not show any significant magnetic anisotropy, while Mn atoms in the Mn⁻TCNQ MOCNs are coupled antiferromagnetically and do show a weak magnetic anisotropy with in-plane magnetization. We explain these observations using both a model Hamiltonian based on mean-field Weiss theory and density functional theory calculations that include spin⁻orbit coupling. Our main conclusion is that the antiferromagnetic coupling between Mn spins and the in-plane magnetization of the Mn spins can be explained by neglecting effects due to the presence of the Au(111) surface, while for Ni⁻TCNQ the metal surface plays a role in determining the absence of magnetic anisotropy in the system.
研究了定位在二维金属-有机配位网络（MOCN）中 3d 过渡金属原子位置的自旋的磁各向异性和交换耦合，该网络生长在 Au(111)金属表面上。特别是，我们考虑了由 Ni 或 Mn 金属中心通过 7,7,8,8-四氰基对醌二甲烷（TCNQ）有机配体连接而成的 MOCN，它们以 1:1 的化学计量比形成矩形网络。基于在 T = 2.5 K 下采集的 X 射线磁圆二色性（XMCD）数据的分析，我们发现 Ni⁻TCNQ MOCN 中的 Ni 原子呈铁磁耦合，且不显示任何显著的磁各向异性，而 Mn⁻TCNQ MOCN 中的 Mn 原子呈反铁磁耦合，且表现出弱的面内磁化磁各向异性。我们使用基于平均场 Weiss 理论的模型哈密顿量和包括自旋-轨道耦合的密度泛函理论计算来解释这些观察结果。我们的主要结论是，Mn 自旋之间的反铁磁耦合和面内 Mn 自旋的磁化可以通过忽略由于存在 Au(111)表面而产生的效应来解释，而对于 Ni⁻TCNQ，金属表面在确定系统中不存在磁各向异性方面起着作用。
