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Impurity effets in coupled-ladder BiCu2PO6 : NMR and QMC

L. K. Alexander, J. Bobroff, A. V. Mahajan, B. Koteswararao, N. Laflorencie, F. Alet

par Webmaster - 4 janvier 2010

Phys. Rev. B 81, 054438 (2010), arXiv:0912.4353

We present a ^{31}P NMR study of the coupled spin 1/2 ladder compound BiCu_2PO_6. In the pure material, intrinsic susceptibility and dynamics show a spin gap of about \Delta=35-40K. Substitution of non magnetic Zn or magnetic Ni impurity at Cu site induces a staggered magnetization which results in a broadening of the ^{31}P NMR line, while susceptibility far from the defects is unaffected. The effect of Ni on the NMR line broadening is twice that of Zn, which is consistent with Quantum Monte Carlo (QMC) calculations assuming that Ni couples ferromagnetically to its adjacent Cu. The induced moment follows a 1/T temperature dependence due to the Curie-like development of the moment amplitude while its extension saturates and does not depend on impurity content or nature. This allow us to establish a generic scenario for impurity doping : in an antiferromagnetically correlated low dimensional spin system with antiferromagnetic correlations, any type of impurity induces a staggered moment at low temperature, whose extension is not linked to the impurity nature but to the intrinsic physics at play in the undoped pure system, from 1D to 2D systems.