Magnetic versus nonmagnetic doping effects on the magnetic ordering in the Haldane chain compound PbNi2V2O8

TL;DR

This study investigates how magnetic and nonmagnetic dopants influence the magnetic ordering in the Haldane chain compound PbNi2V2O8, revealing that the spin nature of dopants critically affects the stability and characteristics of induced magnetic order.

Contribution

It provides new insights into impurity-driven magnetic phase transitions in Haldane chains, highlighting the contrasting effects of magnetic versus nonmagnetic doping on magnetic order stability.

Findings

Nonmagnetic doping induces a metamagnetic transition at low fields.

Magnetic doping sustains magnetic order at higher fields and temperatures.

NMR confirms staggered impurity-induced spin degrees of freedom.

Abstract

A study of an impurity driven phase-transition into a magnetically ordered state in the spin-liquid Haldane chain compound PbNi2V2O8 is presented. Both, macroscopic magnetization as well as 51V nuclear magnetic resonance (NMR) measurements reveal that the spin nature of dopants has a crucial role in determining the stability of the induced long-range magnetic order. In the case of nonmagnetic (Mg2+) doping on Ni2+ spin sites (S=1) a metamagnetic transition is observed in relatively low magnetic fields. On the other hand, the magnetic order in magnetically (Co2+) doped compounds survives at much higher magnetic fields and temperatures, which is attributed to a significant anisotropic impurity-host magnetic interaction. The NMR measurements confirm the predicted staggered nature of impurity-liberated spin degrees of freedom, which are responsible for the magnetic ordering. In addition, differences in the broadening of the NMR spectra and the increase of nuclear spin-lattice relaxation in doped samples, indicate a diverse nature of electron spin correlations in magnetically and nonmagnetically doped samples, which begin developing at rather high temperatures with respect to the antiferromagnetic phase transition.