Light-induced spin-crossover magnet

Abstract

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.

Shape effects on the cluster spreading process of spin-crossover compounds analyzed within an elastic model with Eden and Kawasaki dynamics

“…These properties form the basis of promising applications, such as memory devices, sensors or actuators. [4][5][6] The hysteresis properties have required the use of the concept of cooperativity as a result of short range and long range interactions which favor the spreading of clusters of molecules in the same spin state, the so-called like-spin domains. However, until a few years ago, only indirect proofs for the existence of domains, such as the experimental determination of minor hysteresis loops 7 or Raman spectroscopy results, 8 were available.…”

Aperiodic Spin State Ordering of Bistable Molecules and Its Photoinduced Erasing

“…Light is known to be an efficient control parameter in the prototype photoactive SC materials 12,[20][21][22]30 , and it was shown for [Fe II H 2 L 2-Me ] that weak laser irradiation at 532 nm can promote the molecules from LS to HS 25,26,28 . Fig.…”

“…Fe(II)-based spin crossover (SC) compounds are prototypic bi-stable molecular systems. Both basic scientific research 20 , as well as potential technological applications were investigated, because of ultrafast-switching 21 , information storage or visual displays 13,22 abilities. The possibility offered by various external control parameters such as temperature, pressure or light irradiation for balancing the relative population between low-spin (LS, S=0) and high-spin (HS, S=2) states has attracted much interest and many such complexes have been widely studied over the past decades 12 . In addition to simple entropy-driven macroscopic conversion from LS to HS, complex phenomena resulting from the partial spin conversion and the periodic ordering of HS and LS states around stepped transitions have been described 23,24,25,26 .…”

“…In the full structure model of a modulated structure 20 , the atoms must be described by their positions in the average 3D unit cell and by their modulation functions along the fourth dimension coordinate x 4 of the superspace.…”

Enhanced Activity and Acid pH Stability of Prussian Blue-type Oxygen Evolution Electrocatalysts Processed by Chemical Etching

“…Besides, if this transition occurs with hysteresis a memory effect is conferred. In very recent years there is a renaissance of SCO materials in molecular magnetism [6][7][8][9][10][11][12] because, in contrast with other bistable species such as single molecule magnets, [13,14] SCO may occur at room temperature.…”