Recipes for enhanced molecular cooling

Abstract

Molecular nanomagnets are considered valid candidates for magnetic refrigeration at low temperatures. Designing these materials for enhanced cooling requires the control and optimization of the quantum properties at the molecular level, in particular: spin ground state, magnetic anisotropy, and presence of low-lying excited spin states. Herein, we present the theoretical framework together with a critical review of recent results, and perspectives for future developments.

High spin cycles: topping the spin record for a single molecule verging on quantum criticality

“…As one can see, the entropy changes for ΔB = 7 T are very similar for the actual α = 0.65 of 1 (red) and the critical value of α c = 0.7 (dashed red). The very steep rise at the lowest temperatures signals that this compound should be a powerful cooler at liquid helium temperatures [40][41][42] with impressive MCE figures for a single molecule unit [ΔS = S(7 T)-S(0 T) > 20 R at T≈3 K]. This behaviour is compared in Fig.…”

“…Figure 6 displays the isothermal entropy change, one figure of merit among magnetocaloric properties, 40,41 calculated for the model system Fe 6 Gd 6 . As one can see, the entropy changes for ΔB = 7 T are very similar for the actual α = 0.65 of 1 (red) and the critical value of α c = 0.7 (dashed red).…”

Synthesis, Crystal Structures, and Magnetic Properties of Lanthanide (III) Amino-Phosphonate Complexes

“…Previous results from our group and others indicate that the alkyl groups attached to the aminophosphonic acid has a strong effect on the structures and properties of the lanthanide(III) phosphonates isolated [38,39]. The aminophosphonic acids, H 2 NRPO 3 H 2 (R = alkyl or aryl group), have been proved to be very useful ligands for the synthesis of metal phosphonates with new structure types in which the organic part plays a controllable spacer role and the two inorganic-PO 3 groups chelate with metal ions to form one-, two-, and three-dimensional structures [64,65]. The entropy value for Gadolinium containing complex is 34.5 J kg −1 K −1 , this value being larger than the value of 32.3 J kg −1 K −1 of a previously studied octametallic 4f-phosphonate horseshoes complex {Gd 8 P 6 } [13] for a field change ∆H = 7 T at 3 K. Our future research efforts will be devoted to the syntheses, crystal structures, and magnetic properties of lanthanide(III) compounds of other related amino-phosphonate ligands.…”

Crystal structure of bis(2,6-dihydroxymethyl)pyridine-κ3 N,O,O′)-bis(μ2-6-chloropyridin-2-olato-κ3 N,O:O)-bis(6-chloropyridin-2-olato-κO)-bis(nitrato-κ2 O,O′)digadolinium(III), C34H30Cl4Gd2N8O14

“…eld, and the strong impetus for rapid development originates from the potential applications of such materials as energye cient and environmentally friendly cryogenic refrigerators [1,2]. The Gd 3+ with seven unpaired 4f electrons was preferentially selected to construct molecular units with high MCE because the intrinsic nature of Gd 3+ ful ls the requirements of improving MCEs, such as having a large spin ground state S, negligible magnetic anisotropy and low-lying excited spin states [3,4].…”