On the effect of a regular S=1 dilution of S=1/2 antiferromagnetic Heisenberg chains obtained from quantum Monte Carlo simulations

The effect of an S-1 = 1 regular dilution in an S-2 = 1/2 isotropic antiferromagnetic chain is investigated with quantum Monte Carlo simulations. Our numerical results show that there exist two kinds of ground state phases with different variations of the S-1 = 1 concentration. When the effective spin in a unit cell is half-integer, the ground state is ferromagnetic with a gapless energy spectrum, and the magnetism is continuously weakened as the spin S' concentration p decreases. When the effective spin in a unit cell is integer, however, a non-magnetic ground state with a gapped energy spectrum emerges, and the gap decays gradually, with Delta approximate to 1.25 root rho.