Light-induced spin-state switching in the mixed crystal series of the 2D coordination network {[Zn_1−xFe_x(bbtr)₃](BF₄)₂}_∞: optical spectroscopy and cooperative effects

Abstract

Depending on the iron(ii) concentration, the mixed crystals of {[Zn1-xFex(bbtr)3](BF4)2}∞, bbtr = 1,4-di(1,2,3-triazol-1-yl)butane, 0.01 ≤ x ≤ 1, show macroscopic light-induced bistability between the high-spin and the low-spin state. In the highly diluted system with x = 0.01 and up to x = 0.31, the photoinduced low-spin state always relaxes back to the high-spin state independent of the initial light-induced low-spin fraction. In the highly concentrated mixed crystals with x = 0.67, 0.87 and 1, the strong cooperative effects coupled to a crystallographic phase transition result in light-induced bistability with decreasing critical light-induced low-spin fraction and increasing hysteresis width for increasing iron(ii) concentrations. The lower limit for the light-induced bistability was estimated to be x ≈ 0.5.

Phase diagrams and free-energy landscapes for model spin-crossover materials with antiferromagnetic-like nearest-neighbor and ferromagnetic-like long-range interactions

“…In this paper we have presented detailed phase diagrams, free-energy landscapes, and order-parameter distributions for a model SC material with antiferromagnetic-like nearest-neighbor and ferromagnetic-like long-range interactions [24], covering a wide range of tem- [13,15,21,22]. Topologically different phase diagrams are obtained, depending on the strength of A.…”

“…In the case of optical excitation into the metastable phase, this phenomenon is known as light-induced excited spin trapping (LIESST) [9,11,17]. The metastable properties in combination with the SC materials' sensitivity to a wide range of external stimuli make them promising candidates for applications such as switches, displays, memory devices, sensors, and actuators [13,15,21,22].…”

Equilibrium, metastability, and hysteresis in a model spin-crossover material with nearest-neighbor antiferromagnetic-like and long-range ferromagnetic-like interactions

“…Due to the higher degeneracy of the excited HS state, crystals of such molecules can be brought into a majority HS state by increasing temperature, changing pressure or magnetic field, or by exposure to light. 8,[13][14][15][16][17] If the intermolecular interactions are sufficiently strong, this change of state can become a discontinuous phase transition such that the HS phase becomes metastable and hysteresis occurs. 13,18 In the case of optical excitation into the metastable phase, this effect is known as light-induced excited spin-state trapping (LIESST).…”

A critical review of the T(LIESST) temperature in spin crossover materials − What it is and what it is not

“…Additionally, this hidden hysteresis can be revealed by light irradiation. The compounds reported by Chakraborty et al [49] Tokoro et al [50] belongs to this class III since the HS phase can be erased by light in the temperature range expected for the hidden hysteresis. This peculiar situation that affords a hidden transition is of particular interest since the photoswitching implies two longlived phases.…”