Electronic and magnetic properties of K$_{2}$CuP$_{2}$O$_{7}$ - a model S=1/2 Heisenberg chain system

TL;DR

This study investigates K$_{2}$CuP$_{2}$O$_{7}$ as a model S=1/2 Heisenberg chain system, combining experimental measurements and band structure calculations to confirm its one-dimensional magnetic behavior and lack of long-range order.

Contribution

It provides comprehensive experimental and theoretical evidence that K$_{2}$CuP$_{2}$O$_{7}$ is an excellent realization of a nearest neighbor S=1/2 Heisenberg antiferromagnetic chain.

Findings

NMR shift fits HAF model with J₁ ≈ 141 K

Relaxation rate becomes temperature independent below 30 K

No evidence of magnetic order above 2 K

Abstract

The electronic and magnetic properties of K$_{2}$CuP$_{2}$O$_{7}$ were investigated by means of susceptibility, specific heat and $^{31}$P nuclear magnetic resonance (NMR) measurements and by LDA band structure calculations. The temperature dependence of the NMR shift $K(T)$ is well described by the $S=1/2$ Heisenberg antiferromagnetic chain (HAF) model with nearest neighbor exchange $J_{1}$ $\simeq $ $(141\pm 5)$ K. The corresponding mapping of an LDA-derived tight-binding model leads to $J_{1}^{LDA}$ $\simeq$ 196 K. The spin lattice relaxation rate $1/T_{1}$ decreases with temperature below 300 K but becomes nearly temperature independent between 30 K and 2 K as theoretically expected for an $S = {1/2}$ HAF chain. None of the investigated properties give any evidence for long range magnetic order above 2K, in agreement with the results of the band structure calculation, which yield extremely weak exchange to the next nearest neighbor (NNN) and a very small and frustrated inter-chain exchange. Thus, K$_{2}$CuP$_{2}$O$_{7}$ seems to be a better realization of a nearest neighbor $S = {1/2}$ HAF chain than the compounds reported so far.