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Pré-Publication, Document De Travail Année : 2023

Molecules with two electronic energy levels : thermal hysteresis in a set of two molecules linked by a chemical bond

Résumé

A spin-conversion molecule is organised around an iron ion F e +2. This ion has two quantum energy levels : a low spin (LS) ground level, S = 0, and a high spin (HS) excited level, S = 2 , where S is the total spin of the 3d electrons. A macroscopic crystal of a spin-conversion molecule has two thermodynamic phases : a diamagnetic phase where all the molecules are in (LS) level and a paramagnetic phase where they are all in (HS) level. The diamagnetic phase is stable at low temperature. For some spin-conversion crystals, the phase change is accompanied by a thermal hysteresis cycle and for some of them, this hysteresis still exists in very small nanoparticles. From what size this hysteresis can appear and which are the microscopic parameters responsible for it ? It has been shown that a single spin-conversion molecule passes without hysteresis from one level to the other when its temperature varies. In the present theoretical study we consider the case of two spin conversion molecules linked by a chemical bound. We assume that the value of the elastic force constant of the spring between the two molecules depends on the quantum states of the molecules. A thermal hsyteresis cycle can be obtained.

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Dates et versions

hal-03945906 , version 1 (18-01-2023)
hal-03945906 , version 2 (05-03-2023)
hal-03945906 , version 3 (21-05-2023)
hal-03945906 , version 4 (13-07-2023)

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  • HAL Id : hal-03945906 , version 1

Citer

J.A. Nasser. Molecules with two electronic energy levels : thermal hysteresis in a set of two molecules linked by a chemical bond. 2022. ⟨hal-03945906v1⟩
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