Magnetic susceptibility in quasi one-dimensional Ba2V3O9: chain segmentation versus the staggered field effect

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A pronounced Curie-like upturn of the magnetic susceptibility chi(T) of the quasi one-dimensional spin chain compound Ba2V3O9 has been found recently. Frequently this is taken as a signature for a staggered field mechanism due to the presence of g-factor anisotropy and Dzyaloshinskii-Moriya interaction. We calculate this contribution within a realistic structure of vanadium 3d- and oxygen 2p-orbitals and conclude that this mechanism is far too small to explain experimental results. We propose that the Curie term is rather due to a segmentation of spin chains caused by broken magnetic bonds which leads to uncompensated S=1/2 spins of segments with odd numbers of spins. Using a finite-temperature Lanczos method we calculate their effective moment and show that 1% of broken magnetic bonds is sufficient to reproduce the anomalous low-T behavior of chi(T) in Ba2V3O9.