Spin dilution in frustrated two-dimensional S=1/2 antiferromagnets on a square lattice -: art. no. 174425

Li-7 and Si-29 nuclear magnetic resonance, muon spin relaxation (mu SR), and magnetization measurements in Li2V1-xOTixSiO4, for 0 <= x <= 0.2, are presented. The x=0 compound is a prototype of frustrated two-dimensional Heisenberg antiferromagnet on a square-lattice with competing nearest-(J(1)) and next-nearest-(J(2))neighbor exchange interactions. Ti4+(S=O) for V4+(S= 1/2) substitution yields the spin dilution of the antiferromagnetic layers. The analysis of the magnetization and of the nuclear spin-lattice relaxation rate shows that spin dilution not only reduces the spin stiffness by a factor similar or equal to(1 - x)(2), but also causes the decrease of the effective ratio J(2)(x)/J(1)(x). Moreover, the sublattice magnetization curves derived from zero-field ASR measurements in the collinear phase point out that, at variance with nonfrustrated two-dimensional Heisenberg antiferromagnets, spin dilution affects the low-temperature staggered magnetization only to a minor extent. This observation is supported also by the x dependence of the collinear ordering temperature. The results obtained for the Ti doped samples are discussed in the light of the results previously obtained in the pure x = 0 compound and in nonfrustrated two-dimensional Heisenberg anti ferromagnets with spin dilution.