Influence of magnetic interaction between impurity and impurity-liberated spins on the magnetism in the doped Haldane chain compounds PbNi${}_{2-x${A}${}_{x}$V${}_{2}$O${}_{8}$ (A = Mg, Co)

TL;DR

This study investigates how magnetic and nonmagnetic impurities affect magnetism in doped PbNi${}_{2}$V${}_{2}$O${}_{8}$, revealing impurity-host interactions and relaxation processes through ESR and susceptibility measurements.

Contribution

It provides new quantitative estimates of impurity-liberated spin interactions and impurity-host exchange in doped Haldane chain compounds using ESR and susceptibility data.

Findings

Magnetic Co doping causes severe ESR line broadening due to rapid spin-lattice relaxation.

Exchange parameters explain low-temperature magnetization behavior.

Impurity-liberated spins interact differently depending on impurity type.

Abstract

A comprehensive study of impurity-induced magnetism in nonmagnetically (Mg${}^{2+}$) and magnetically (Co${}^{2+}$) doped PbNi${}_{2}$V${}_{2}$O${}_{8}$ compounds is given, using both macroscopic dc susceptibility and local-probe electron spin resonance (ESR) techniques. Magnetic coupling between impurity-liberated spins is estimated from a linewidth of low-temperature ESR signal in Mg-doped samples. In addition, in the case of magnetic cobalt dopants the impurity-host magnetic exchange is evaluated from the Co-induced contribution to the linewidth in the paramagnetic phase. The experimentally observed severe broadening of the ESR lines in the magnetically doped compounds with respect to nonmagnetic doping is attributed to a rapid spin-lattice relaxation of the Co${}^{2+}$ ions, which results in a bottleneck-type of temperature dependence of the induced linewidth. The exchange parameters obtained from the ESR analysis offer a satisfactory explanation of the observed low-temperature magnetization in doped samples.