Photomagnetic Properties of Some Inorganic Solids

Examples of molecular switching in inorganic solids, due to temperature, light, pressure, and magnetic field

“…The reversibility of the photoprocess is, of course, appealing for applications to optical information storage, and similar effects have been reported for the PBAs [6]. In the case of SC, photoexcitation usually occurs as a bleaching effect [23b], for both the direct and reverse processes [2]. A useful scheme is the Jablonski diagram, which has been reproduced many times, see ref.…”

“…Because of both electronic and vibrational factors, ∆S > 0, therefore, g >> 1. The Ising-like model has been used for describing the static [12] and dynamic [13] properties of SC solids, and was applied as well to the VT compound [2]. The Ising Hamiltonian writes: (1) with fictitious spins r having eigenvalues +1 in the HS state, -1 in the LS state, and degeneracies gHS, gLS, and ∆ = E(HS)-E(LS) denoted energy gap (or "fictitious field") in the following.…”

“…The Ising Hamiltonian writes: (1) with fictitious spins r having eigenvalues +1 in the HS state, -1 in the LS state, and degeneracies gHS, gLS, and ∆ = E(HS)-E(LS) denoted energy gap (or "fictitious field") in the following. The HS fraction is expressed as a function of the "fictitious magnetization": (2) A convenient form of the Ising-like Hamiltonian is the Ising equivalent form [10b], obtained by rewriting the canonical partition function to get rid of the pre-exponential factors. The Ising equivalent form involves a temperature-dependent energy gap (= "fictitious effective field") accounting for the degeneracy ratio: Fig.…”

“…The pressure dependence of the energy gap ∆ = E(HS)-E(LS) merely writes: (9) with δV, the molecular volume increase upon spin conversion, leading to: (10) where ∆V = N δV is the molar volume increase upon total conversion. Most of the experimental data [2,9,36] for the considered families of compounds yield δV ~ 20-30 Å 3 . In Figs.…”

“…A. Ammeter [1]. We report here on several families of inorganic systems [2] where a SC is involved in the switching process between the two molecular states: SC solids, PBAs, valence-tautomeric system (VT), see table below. A previous presentation of the underlying concept of "molecular bistability" was given by O. Kahn [3], on the example of SC solids.…”