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Abstract:
The compound KTi(SO4)(2)center dot H2O was recently reported as a
quasi-one-dimensional spin-1/2 compound with competing antiferromagnetic
nearest-neighbor exchange J(1) and next-nearest-neighbor exchange J(2)
along the chain with a frustration ratio alpha = J(2)/J(1) approximate
to 0.29 [G. J. Nilsen, H. M. Ronnow, A. M. Lauchli, F. P. A. Fabbiani,
J. Sanchez-Benitez, K. V. Kamenev, and A. Harrison, Chem. Mater. 20, 8
(2008)]. Here, we report a microscopically based magnetic model for this
compound derived from density functional theory (DFT) based electronic
structure calculations along with respective tight-binding models. Our
(LSDA+U-d) calculations confirm the quasi-one-dimensional nature of the
system with antiferromagnetic J(1) and J(2), but suggest a significantly
larger frustration ratio alpha(DFT) approximate to 0.94-1.4, depending
on the choice of U-d and structural parameters. Based on transfer matrix
renormalization group (TMRG) calculations we find alpha(TMRG) = 1.5. Due
to an intrinsic symmetry of the J(1)-J(2) model, our larger frustration
ratio alpha is also consistent with the previous thermodynamic data. To
identify the frustration ratio alpha unambiguously, we propose
performing high-field magnetization and low-temperature susceptibility
measurements.
