For the paradigmatic frustrated spin-half Heisenberg antiferromagnet on the kagomé lattice we performed large-scale numerical investigation of thermodynamic functions by means of the finitetemperature Lanczos method for system sizes of up to N = 42. We present the dependence of magnetization as well as specific heat on temperature and external field and show in particular that a finite-size scaling of specific heat supports the appearance of a low-temperature shoulder below the major maximum. This seems to be the result of a counterintuitive motion of the density of singlet states towards higher energies. Other interesting features that we discuss are the asymmetric melting of the 1/3 magnetization plateau as well the field dependence of the specific heat that exhibits characteristic features caused by the existence of a flat one-magnon band. By comparison with the unfrustrated square-lattice antiferromagnet the tremendous role of frustration in a wide temperature range is illustrated.

Cyclic coordination clusters (CCCs) are proving to provide an extra dimension in terms of exotic magnetic behavior as a result of their finite but cyclized chain structures. The Fe 18 Dy 6 CCC is a Single Molecule Magnet with the highest nuclearity among Ln containing clusters. The three isostructural compounds [Fe 18 Ln 6 (μ OH) 6 (ampd) 12 (Hampd) 12 (PhCO 2 ) 24 ](NO 3 ) 6 • 38MeCN for Ln = Dy III (1), Lu III (2), or Y III (3), where H 2 ampd = 2 amino 2 methyl 1,3 propanediol, are reported. These can be described in terms of the cyclization of six {Fe 3 Ln(μOH)(ampd) 2 (Hampd) 2 (PhCO 2 ) 4 } + units with six nitrate counterions to give the neutral cluster. The overall structure consists of two giant Dy 3 triangles sandwiching a strongly antiferromagnetically coupled Fe 18 ring, leading to a toroidal arrangement of the anisotropy axis of the Dy ions, making this the biggest toroidal arrangement on a molecular level known so far.

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