Abstract
A joint experimental and theoretical investigation of the spin 1/2 system suggests a description of this compound as coupled alternating antiferromagnetic Heisenberg chains. Magnetic susceptibility, specific heat, nuclear magnetic resonance, nuclear quadrupole resonance, and high-field magnetization measurements evidence a spin gap of about 25 K. Surprisingly, the leading antiferromagnetic exchange of about 75 K can be assigned by density-functional band-structure calculations to a coupling between the structural dimers, whereas the coupling within these dimers is strongly reduced due to sizable ferromagnetic contributions. The coupling within the structural dimers competes with a number of long-range couplings. The present available experimental data can be consistently described in a scenario of coupled alternating chains. The proposed model should be considered as a minimal model for an appropriate description of this compound.
6 More- Received 7 December 2009
DOI:https://doi.org/10.1103/PhysRevB.81.104416
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