Baker Michael L, Lancaster Tom, Chiesa Alessandro, Amoretti Giuseppe, Baker Peter J, Barker Claire, Blundell Stephen J, Carretta Stefano, Collison David, Güdel Hans U, Guidi Tatiana, McInnes Eric J L, Möller Johannes S, Mutka Hannu, Ollivier Jacques, Pratt Francis L, Santini Paolo, Tuna Floriana, Tregenna-Piggott Philip L W, Vitorica-Yrezabal Iñigo J, Timco Grigore A, Winpenny Richard E P
School of Chemistry and Photon Science Institute, The University of Manchester, Oxford Road, Manchester, M13 9PL, UK.
Institut Laue-Langevin, BP 156, 6 rue Jules Horowitz, 38042, Grenoble Cedex 9, France.
Chemistry. 2016 Jan 26;22(5):1779-88. doi: 10.1002/chem.201503431. Epub 2016 Jan 8.
The spin dynamics of Cr8 Mn, a nine-membered antiferromagnetic (AF) molecular nanomagnet, are investigated. Cr8 Mn is a rare example of a large odd-membered AF ring, and has an odd-number of 3d-electrons present. Odd-membered AF rings are unusual and of interest due to the presence of competing exchange interactions that result in frustrated-spin ground states. The chemical synthesis and structures of two Cr8 Mn variants that differ only in their crystal packing are reported. Evidence of spin frustration is investigated by inelastic neutron scattering (INS) and muon spin relaxation spectroscopy (μSR). From INS studies we accurately determine an appropriate microscopic spin Hamiltonian and we show that μSR is sensitive to the ground-spin-state crossing from S=1/2 to S=3/2 in Cr8 Mn. The estimated width of the muon asymmetry resonance is consistent with the presence of an avoided crossing. The investigation of the internal spin structure of the ground state, through the analysis of spin-pair correlations and scalar-spin chirality, shows a non-collinear spin structure that fluctuates between non-planar states of opposite chiralities.
研究了九元反铁磁（AF）分子纳米磁体Cr8 Mn的自旋动力学。Cr8 Mn是大型奇数元AF环的一个罕见例子，且存在奇数个3d电子。由于存在导致自旋受挫基态的竞争交换相互作用，奇数元AF环并不常见且备受关注。报道了仅在晶体堆积上有所不同的两种Cr8 Mn变体的化学合成及结构。通过非弹性中子散射（INS）和μ子自旋弛豫光谱（μSR）研究了自旋受挫的证据。通过INS研究，我们精确确定了合适的微观自旋哈密顿量，并表明μSR对Cr8 Mn中基态自旋从S = 1/2到S = 3/2的交叉敏感。估计的μ子不对称共振宽度与存在避免交叉相一致。通过对自旋对关联和标量自旋手性的分析，对基态内部自旋结构的研究表明，存在一种非共线自旋结构，该结构在相反手性的非平面状态之间波动。
