Effect of spin-1 impurities in dimerized Heisenberg chains

Abstract

The effects of spin-1 impurities introduced in dimerized antiferromagnetic spin chains are studied using Lanczos diagonalization and quantum Monte Carlo simulations. Firstly, the magnitude of the interaction between a Ni-ion replacing a Cu-ion is derived for the case study system Cu-O-Cu. Then, it is shown that the introduction of S = 1 impurities leads to the suppression of the original spin gap of the dimerized system and to the enhancement of the antiferromagnetic correlations close to the impurity. These features are interpreted in terms of a valence bond picture of the ground state of both the pure and the doped system. The similitudes and differences between the underlying mechanisms that produce these effects in the cases of nonmagnetic and S = 1 impurities are analyzed. It is stressed that a singlet formed between the spin-1 impurity site and the two spin-1/2 neighbors spins behaves as an effective nonmagnetic vacancy which may be partially responsible for the enhancement of the antiferromagnetic correlations on the whole system. Implications of these results for experiment are also discussed.

Slow relaxation experiments in disordered charge and spin density waves: collective dynamics of randomly distributed solitons

“…These substitutions generate either 3D antiferromagnetism at low temperature (in the case of CuGeO 3 and PbNi 2 V 2 O 8 ) or strong 3D antiferromagnetic correlations (in the case of Y 2 BaNiO 5 ). In these two types of low dimensional spin models, the non magnetic defects generate spin-1/2 moments out of the non magnetic ground state, either in the form of solitons in spin-Peierls systems [31][32][33][34][35][36][37][38], or in the form of "edge" spin-1/2 moments in Haldane gap systems [39][40][41][42]. The available theoretical description of these systems is based on the Dasgupta-Ma real space RG [11,43] describing non magnetic defects in 1D and quasi-1D geometries [30,44,45], and appears to be in good agreement with experiments.…”

Synthesis, Structural and Magnetic Properties of the Solid Solution (CuCl1-xBrx)LaNb2O7 (0 ≤x ≤1)

“…So far, there have been many theoretical works on the rapid breaking of spin-singlet dimers upon the addition of vacancies in a variety of spingapped models, a procedure which is considered relevant to creating free spins. Some theories showed that staggered spin-spin correlations are enhanced in the vicinity of spin vacancies, [25][26][27][28][29] which accounts for the emergence of the ordered phase in the cationic-substituted 1D magnetic materials CuGeO 3 and SrCu 2 O 3 . 9,10) In the 2D orthogonal dimer SrCu 2 (BO 3 ) 2 , staggered magnetization develops around the triplet excitation in the 1/8 plateau phase.…”

Low-energy excitations of spin-Peierls chains with modified bond impurities

“…In the limit x → −∞ one recovers the case of a spin-1 impurity (corresponding to a Ni → Cu substitution) previously studied. 23 Precisely in Ref. 23 it was emphasized the role of the three-site subsystem composed by the S = 1 site and its two S = 1/2 NN sites.…”

“…23 Precisely in Ref. 23 it was emphasized the role of the three-site subsystem composed by the S = 1 site and its two S = 1/2 NN sites.…”