## Rotating Magnetocaloric Effect in an Anisotropic Two-Dimensional
Cu^{II}[W^{V}(CN)_{8}]^{3–} Molecular Magnet with Topological Phase Transition: Experiment and
Theory

journal contribution

posted on 15.09.2017, 19:49 by Piotr Konieczny, Robert Pełka, Dominik Czernia, Robert PodgajnyConventional (MCE)
and rotating (RMCE) magnetocaloric effects have been explored in the
two-dimensional (2D) coordination polymer {(tetren)H

_{5})_{0.8}Cu^{II}_{4}[W^{V}(CN)_{8}]_{4}·7.2H_{2}O}_{n}(**WCu-t**; tetren = tetraethylenepentamine). The unusual magnetostructural properties were exploited, including the bilayered Prussian Blue like coordination skeleton and the*XY*easy-plane magnetic anisotropy based on the*in-plane*correlation between W^{V}and Cu^{II}spins of^{1}/_{2}, underlying the Berezinskii–Kosterlitz–Thouless (BKT) topological phase transition to the long-range-ordered state at*T*_{C}= 33 K. The magnetic properties were studied on single crystals along the*H*∥*ac*easy plane and*H*∥*b*hard axis. The maximal entropy change for MCE for easy-plane geometry at 38.0 K and the magnetic field change μ_{0}Δ*H*= 7.0 T reached ∼4.01 J K^{–1}kg^{–1}. The strong magnetic anisotropy was used to study the RMCE in which the maximal entropy change was observed at 35.5 K for 7.0 T, attaining 1.81 J K^{–1}kg^{–1}. Moreover, easy-plane anisotropy introduces the inverse magnetocaloric effect for*H*∥*b*, which enhances the RMCE by up to 47%. This observation was confirmed by a theoretical investigation considering the*XY*model using a molecular field and cluster variational method in the pair approximation approach, dedicated to the bilayered systems with the adequate nearest neighbor number*z*= 5 and spin*S*=^{1}/_{2}.#### Read the peer-reviewed publication

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coordinationpair approximation approachW Vbilayered Prussian Blueeasy-planeRMCEanisotropycluster variational method0.8 Cu II 4entropy changetetrenBKTCNTopological Phase TransitionXYAnisotropic Two-Dimensional Cu IImagnetocaloricneighbor number zRotating Magnetocaloric Effectkg7.0 TMCEtopological phase transitionfield change μ 0 Δ H

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#### Read the peer-reviewed publication

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### Keywords

coordinationpair approximation approachW Vbilayered Prussian Blueeasy-planeRMCEanisotropycluster variational method0.8 Cu II 4entropy changetetrenBKTCNTopological Phase TransitionXYAnisotropic Two-Dimensional Cu IImagnetocaloricneighbor number zRotating Magnetocaloric Effectkg7.0 TMCEtopological phase transitionfield change μ 0 Δ H