Ordered State in a Haldane Material PbNi$_2$V$_2$O$_8$ Doped with Magnetic and Non-Magnetic Impurities

TL;DR

This study investigates how different magnetic and non-magnetic impurities induce three-dimensional magnetic order in the Haldane material PbNi2V2O8, revealing impurity-specific effects on transition temperatures and underlying interactions.

Contribution

It provides the first comprehensive phase diagrams for impurity-doped PbNi2V2O8 and explains the impurity-dependent transition temperatures using an effective Hamiltonian based on the VBS model.

Findings

Universal occurrence of 3D order in doped samples

Transition temperatures strongly depend on impurity species

Effective interactions include ferromagnetic and antiferromagnetic components

Abstract

Impurity effect is systematically studied in doped Haldane material Pb(Ni$_{1-x}$$M_x$)$_2$V$_2$O$_8$ ($M$ = Mn, Co, Cu, and Mg) by use of DC and AC susceptibility, and heat capacity measurements. The occurrence of three-dimensional ordered state is universally observed for all the impurities and the complete temperature -- concentration phase diagrams are obtained, which are qualitatively similar to that in other spin-gap materials. The unique feature is found in the drastic dependence of the transition temperatures on the species of the impurities. The consideration of effective Hamiltonian based on VBS model makes it clear that the ferromagnetic next-nearest-neighbor interaction and the antiferromagnetic nearest-neighbor interaction between impurity and edge spins play a key role in the unique feature.