Magnetic susceptibility in quasi one-dimensional Ba_a2V₃O₉: chain segmentation versus the staggered field effect

Abstract:

A pronounced Curie-like upturn of the magnetic susceptibility x (T) of the quasi one-dimensional spin chain compound Ba₂V₃O₉ has been found recently [1]. 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 3 d- 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 = ½ spins of segments with odd numbers of spins. Using the 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 x(T) in Ba₂V₃O₉.