Spin dilution in frustrated two-dimensional S=1/2 antiferromagnets on a square lattice

7Li and 29Si nuclear magnetic resonance, muon spin relaxation (muSR), and magnetization measurements in Li2V1−xOTixSiO4, for 0<x<0.2, are presented. The x=0 compound is a prototype of frustrated twodimensional Heisenberg antiferromagnet on a square-lattice with competing nearest- (J1) and next-nearest- (J2) neighbor exchange interactions. Ti4+(S=0) 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 .around (1−x)^2, but also causes the decrease of the effective ratio J2(x) /J1(x). Moreover, the sublattice magnetization curves derived from zero-field muSR 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 antiferromagnets with spin dilution.