Quenched charge disorder in CuO2 spin chains: Experimental and numerical studies

TL;DR

This study combines experimental measurements and Monte Carlo simulations to investigate how quenched charge disorder affects magnetic properties and spin order in lightly hole-doped CuO2 spin chains, revealing disorder-induced smearing of the spin-flop transition.

Contribution

It provides new experimental and numerical evidence that quenched charge disorder destroys the sharp spin-flop transition in CuO2 spin chains.

Findings

Disorder causes broad anomalies in magnetic susceptibility.

Monte Carlo simulations show smearing of the spin-flop transition due to holes.

Experimental data aligns qualitatively with simulation results.

Abstract

We report on measurements of the magnetic response of the anisotropic CuO_2 spin chains in lightly hole-doped La_x (Ca,Sr)_14-x Cu_24 O_41, x>=5. The experimental data suggest that in magnetic fields B >~ 4T (applied along the easy axis) the system is characterized by short-range spin order and quasi-static (quenched) charge disorder. The magnetic susceptibility chi(B) shows a broad anomaly, which we interpret as the remnant of a spin-flop transition. To corroborate this idea, we present Monte Carlo simulations of a classical, anisotropic Heisenberg model with randomly distributed, static holes. Our numerical results clearly show that the spin-flop transition of the pure model (without holes) is destroyed and smeared out due to the disorder introduced by the quasi-static holes. Both the numerically calculated susceptibility curves chi(B) and the temperature dependence of the position of the anomaly are in qualitative agreement with the experimental data.