Abstract
The magnetothermodynamic properties of the low-dimensional 2-D metal organic framework (MOF) halide series, Cu9X2(cpa)6 (X = F, Cl, Br; cpa = anion of 2-carboxypentonic acid), abbreviated as CPA(X), has been the subject of experimental studies suggesting the tunability of magnetic properties via halide and guest-host chemistry. CPA(X) is best described as a topologically spin frustrated triangles-in-triangles or triangulated-Kagome-lattice (TKL) on a layered MOF. CPA(X) consists of microporous channels (oriented transverse to the layers) available for chemical manipulation, which support tunability of properties and the further expansion of this class of materials. While the spin frustrated topology of CPA(Cl) has been shown to exhibit a magnetocaloric effect (MCE) at temperatures less than 10 K, we report here new temperature- and field-dependent magnetization data for CPA(Br). In this study, we estimate the effect of halide interchangeability on the MCE produced by this system in low field and at cryogenic temperatures. Magnetic entropy change (ΔS), relative cooling power (RCP), and refrigerant capacity (RC) are calculated for this material and the effects of halide interchangeability on the MCE are discussed. The CPA(X) series, as a tunable molecular magnet, may also serve as a candidate for quantum spin liquid (QSL) studies and invites chemical manipulation of its magnetic properties, including the MCE.
Highlights
Space-based applications, superconducting magnets, quantum computing, and detector technologies are all of interest currently for the application of refrigeration at cryogenic temperatures.[1]
The complexities of helium dilution refrigerators that are associated with the issues of gas compression/expansion has led to the use of adiabatic demagnetization refrigeration (ADR) for low gravity applications, where ADR depends on the magnetocaloric effect (MCE) of a material
Beyond interests in MCE materials, enhanced spin frustration allows for the study of the fundamental physics in quantum spin liquids (QSLs).[2,3]
Summary
Space-based applications, superconducting magnets, quantum computing, and detector technologies are all of interest currently for the application of refrigeration at cryogenic temperatures.[1]. Simple paramagnetic salts exhibiting a useful MCE – defined by refrigerant capacity (RC), relative cooling power (RCP), adiabatic temperature change (ΔTad), and maximum entropy change (ΔSM,max) at applied fields – have been used to meet this need to date. The MCE for frustrated systems is expected to be enhanced and assists in reducing the temperature at which the onset of magnetic ordering occurs because of the resilient entropy that exists due to a frustrated ground state.[4,5] Strongly frustrated Heisenberg antiferromagnets (e.g., Kagome, garnet, and pyrochlore lattices) exhibit. Framework is a topologically unique 2-D triangulated-Kagome lattice (TKL) and exhibits a considerably large spin-frustration ratio, θCW/Tc, the signature metric of highly frustrated systems.[17–20]. Recent field-dependent heat capacity data[25] for CPA(Cl) exhibits a boundary resembling that found for Herbertsmithite[44] in which it separates a Landau Fermi liquid (LFL) phase from a non-. We report here the MCE for CPA(Br) from magnetization data and discuss the effect of MCE tunability via halide substitution in CPA(X)
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