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Abstract:
We present low-temperature susceptibility data on a spinS=12dimersystem consisting of nitronyl-nitroxid radicals which are bridged viatolan molecules. The material, exhibiting a double-layer structure,can be regarded as a quasi- 2D system. From SQUID magnetisationmeasurements on high-quality single crystals, an intra-dimer couplingconstant ofJintra/kB≈9.6 K can be determined. In addition, thedata reveal indications for an inter-dimer coupling of the order of 1 K.In order to look for magnetic field-induced ordering phenomena, AC-susceptibility measurements were performed down to temperatures aslow asT= 34 mK and magnetic fields up toB= 10.5 T. For temperatures belowT= 250 mK, a double-peak structure was observedat fields between 8 T and 9.5 T consistent with the expectation basedon the above-mentioned coupling constants. Furthermore, in the sametemperature range another anomaly aroundB= 4.5 T appears. Fora detailed understanding especially with regard to the dimensionalityof the interactions and the implications for the type of order that isrealized here, Quantum Monte Carlo simulations are underway.
