Formation of random singlets in the nanocrystalline quasi-one-dimensional spin-1/2 antiferromagnet Sr21Bi8Cu2(CO3)2O41

TL;DR

This study investigates the formation of random singlet states in nanocrystalline Sr21Bi8Cu2(CO3)2O41, revealing unique exchange interaction distributions influenced by finite size effects, through comprehensive thermodynamic measurements.

Contribution

It demonstrates the presence of random-singlet spin pairs with unconventional exchange interaction distributions in a nanocrystalline quasi-one-dimensional antiferromagnet, highlighting finite size effects.

Findings

Random-singlet states with logarithmic P(J) in zero field.

P(J) proportional to 1/J in magnetic fields.

Scaling functions accurately fit thermodynamic data.

Abstract

Induced by quenched disorder, random-singlet states occur in a variety of low-dimensional spin-1/2 antiferromagnets, some of them candidates for quantum spin liquids. Here we report measurements of the specific heat, magnetization, and magnetic susceptibility of nanocrystalline Sr21Bi8Cu2(CO3)2O41, a quasi-one-dimensional spin-1/2 antiferromagnet with alternating bonds. The results uncover the predominant presence of random-singlet spin pairs in this material, with a logarithmic probability distribution, P(J), of the renormalized, emergent exchange interaction, J, in zero magnetic field and P(J) proportional to 1/J in magnetic fields. We postulate that these unexpected J dependences, in contrast to the usual P(J) \propto 1/$J^\gamma$ with 0 < $\gamma$ < 1, and possibly also the dichotomy, arise from the finite size of the nanocrystals. Scaling functions for the specific heat and magnetization reproduce our magnetocaloric-effect data, with no adjustable parameters.