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Anisotropy And 3d-4f Magnetic Exchange Interactions

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relaxation barrier depends on both single-ion anisotropy and 3d-4f magnetic exchange interactions.10 Thus when the 3d-4f magnetic exchange coupling is strong enough, the exchange coupled levels are well separated (avoiding mixing of low-lying excited states in the ground state) and the QTM is suppressed, so that large energy barriers, hysteresis loops and relaxation times are observed. It should be noted that only a few heterometallic 3d/4f complexes where the magnetic exchange interaction is able to effectively reduce the QTM process have been reported so far. The best example of this phenomenon, is the family of heterometallic tetranuclear CrIII2 LnIII2 butterfly-like type SMMs complexes recently reported by Murray et al.,10b, 10f, 11…show more content…
MMCs are complexes exhibiting enhanced magneto-caloric effect (MCE), which is based on the change of magnetic entropy upon application of a magnetic field and can be exploited for molecular refrigeration.6 Contrary to SMM behaviour, which is favoured by highly anisotropic Ln3+ ions, the MCE is improved in molecules containing isotropic metal ions and exhibiting weak magnetic coupling between them. This is because in these conditions multiple low-lying excited, field-accessible states are generated, which can contribute to the magnetic entropy of the system. In view of the above considerations, 3d-4f dinuclear complexes containing the isotropic Gd3+ ion, which has the maximum entropy value calculated as Rln(2SGd + 1)/MGd = 110 Jkg-1K-1 and the MnIII ion (despite being anisotropic has a maximum entropy value of 271 Jkg-1K-1) could be good candidates for constructing magnetic coolers. It should be noted that although numerous MnIII/LnIII cluster complexes exist,13 to the best of our knowledge, no examples of fully structurally and magnetically characterized simple dinuclear MnIIILnIII complexes have been reported so far (actually, an example of dinuclear MnIIIGdIII can be found in the literature, but its crystal structure was not reported). This is
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