Department of Chemistry, School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
Nat Chem. 2011 Jun 5;3(7):564-9. doi: 10.1038/nchem.1067.
The light-induced phase transition between the low-spin (LS) and high-spin (HS) states of some transition-metal ions has been extensively studied in the fields of chemistry and materials science. In a crystalline extended system, magnetically ordering the HS sites of such transition-metal ions by irradiation should lead to spontaneous magnetization. Previous examples of light-induced ordering have typically occurred by means of an intermetallic charge transfer mechanism, inducing a change of valence of the metal centres. Here, we describe the long-range magnetic ordering of the extended Fe(II)(HS) sites in a metal-organic framework caused instead by a light-induced excited spin-state trapping effect. The Fe-Nb-based material behaves as a spin-crossover magnet, in which a strong superexchange interaction (magnetic coupling through non-magnetic elements) between photo-produced Fe(II)(HS) and neighbouring Nb(IV) atoms operates through CN bridges. The magnetic phase transition is observed at 20 K with a coercive field of 240 Oe.
在化学和材料科学领域，人们已经广泛研究了一些过渡金属离子的低自旋（LS）和高自旋（HS）态之间的光致相转变。在晶态扩展系统中，通过辐照使这些过渡金属离子的 HS 位有序化，应该会导致自发磁化。以前的光致有序的例子通常是通过金属间电荷转移机制发生的，这会导致金属中心价态的变化。在这里，我们描述了一个由光致激发态捕获效应引起的金属-有机骨架中扩展的 Fe(II)(HS)位的长程磁有序。基于 Fe-Nb 的材料表现为自旋交叉磁体，其中光生成的 Fe(II)(HS)和相邻的 Nb(IV)原子之间通过 CN 桥产生的强超交换相互作用（通过非磁性元素的磁耦合）起作用。在 20 K 时观察到了磁相变，矫顽场为 240 Oe。
