Impurity effects in coupled-ladder BiCu2PO6 studied by NMR and quantum Monte Carlo simulations

TL;DR

This study investigates how impurities affect the magnetic properties of BiCu2PO6 using NMR and quantum Monte Carlo simulations, revealing impurity-induced staggered magnetization and its dependence on impurity type and intrinsic system physics.

Contribution

It demonstrates that impurity doping induces a universal staggered magnetization in low-dimensional antiferromagnetic systems, regardless of impurity nature, supported by NMR data and QMC calculations.

Findings

Ni causes twice the line broadening of Zn, consistent with ferromagnetic coupling.

Induced moments follow a 1/T temperature dependence.

Extension of impurity-induced moments saturates, independent of impurity type.

Abstract

We present a 31P NMR study of the coupled spin 1/2 ladder compound BiCu2PO6. In the pure material, intrinsic susceptibility and dynamics show a spin gap of about . Substitution of non magnetic Zn or magnetic Ni impurity at Cu site induces a staggered magnetization which results in a broadening of the 31P 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 verify the generically expected scenario for impurity doping and to extend it to magnetic impurity case: 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.