Nonmagnetic impurity perturbation to the quasi-two-dimensional quantum helimagnet LiCu(2)O(2)

Abstract

A complete phase diagram of Zn-substituted quantum quasi-two-dimensional helimagnet LiCu(2)O(2) has been presented. Helical ordering transition temperature (T(h)) of the original LiCu(2)O(2) follows finite size scaling for less than similar to 5.5% Zn substitution, which implies the existence of finite helimagnetic domains with domain boundaries formed with nearly isolated spins. Higher Zn substitution >= 5.5% quenches the long-range helical ordering and introduces an intriguing Zn-level-dependent magnetic phase transition with slight thermal hysteresis and a universal quadratic field dependence for T(c)(Zn > 0.055, H). The magnetic coupling constants of nearest-neighbor J(1) and next-nearest-neighbor J(2) (alpha = J(2)/J(1)) are extracted from high temperature series expansion fitting and N = 16 finite chain exact diagonalization simulation. We have also provided evidence of direct correlation between long-range helical spin ordering and the magnitude of electric polarization in this spin-driven multiferroic material.