Conventional (MCE) and rotating (RMCE) magnetocaloric effects have been explored in the two-dimensional (2D) coordination polymer {(tetren)H)Cu[W(CN)]·7.2HO} (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 and Cu spins of /, underlying the Berezinskii-Kosterlitz-Thouless (BKT) topological phase transition to the long-range-ordered state at T = 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 μΔH = 7.0 T reached ∼4.01 J K kg. 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 kg. 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 = /.
Magnetocaloric effect is considered as an energy-efficient and environmentally friendly technique which can take the cooling technology on the next level. Apart from its commercial application around room temperature, the...
Chiral photomagnets
compose a class of multifunctional molecule-based
materials with light-induced alteration of magnetization and chiral
properties. The rational design and synthesis of such assemblies is
a challenge, and only few such systems are known. Herein, the remarkable
octacyanide-bridged enantiomeric pair of 1-D chains [Cu((R,R)-chxn)2]2[Mo(CN)8]·H2O (1R) and [Cu((S,S)-chxn)2]2[Mo(CN)8]·H2O (1S) exhibiting enantiopure structural helicity, which results in optical
activity in the 350–800 nm range as confirmed by natural circular
dichroism (NCD) spectra, is reported. The photomagnetic effects of 1R, 1S, and 1rac result from the
blue light excitation (436 nm) of the photomagnetically active octacyanidomolybdate(IV)
ions. In the excited state MoIV
HS centers with S = 1 couple antiferromagnetically with the neighboring
CuII centers with J
CuMo values
of −1.3, −1.0, and −1.1 cm–1 for 1R, 1S, and 1rac, respectively.
The values of thermal relaxation energy barriers have been estimated
as 142 and 356 K for 1R and 1S, being comparable
with the energy range of the thermal bath. The value for 1rac reveals a significantly lower value of 75 K. On the basis of these
results the value of g
Mo
HS has
been estimated to be in the range 4.8–5.8.
The rotating magnetocaloric effect (RMCE) is a new issue in the field of magnetic refrigeration. We have explored this subject on the two-dimensional (2D) enantiopure {[Mn(R-mpm)][Nb(CN)]}·4HO (where mpm = α-methyl-2-pyridinemethanol) coordination ferrimagnet. In this study, the magnetic and magnetocaloric properties of single crystals were investigated along the bc//H easy plane and the a*//H hard axis. The observed small easy plane anisotropy is due to the dipole-dipole interactions. For fields higher than 0.5 T, no significant difference in the magnetocaloric effect between both geometries was noticed. The maximal magnetic entropy change for conventional effect was observed at 32 K and the magnetic field change μΔH = 5.0 T attaining the value of ∼5 J mol K. The obtained maximal value of -ΔS is comparable to previously reported results for polycrystalline octacyanidoniobate-based bimetallic coordination polymers. A substantial anisotropy of magnetocaloric effect between the easy plane and hard axis appears in low fields. This includes the presence of inverse magnetocaloric effect only for the a*//H direction. The difference between both geometries was used to study the rotating magnetocaloric effect. We show that the inverse part of magnetocaloric effect can be used to enhance the rotating magnetic entropy change up to 51%. This finding is of key importance for searching efficient materials for RMCE.
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