Enhanced magnetocaloric effect via halide substitution in the tunable molecular magnet, Cu9Br2(cpa)6

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.