Crossover from one- to three-dimensional behavior in the S = 1/2 Heisenberg antiferromagnet Cu(N2H5)2(SO4)2

TL;DR

This study maps the magnetic phase diagram of the quasi-one-dimensional antiferromagnet Cu(N2H5)2(SO4)2, revealing a crossover from one-dimensional to three-dimensional magnetic behavior driven by temperature and magnetic field.

Contribution

The paper provides the first complete phase diagram combining experimental and theoretical analyses, including exact quantum-transfer-matrix modeling of the crossover behavior.

Findings

Identification of a broad maximum in specific heat at T_max~2 K

Observation of antiferromagnetic order below T_N~1 K

Determination of intrachain exchange parameter J = 4.25 K

Abstract

From experimental and theoretical analyses of magnetic and specific-heat properties, we present the complete magnetic phase diagram of the quasi-one-dimensional antiferromagnet Cu(N$_2$H$_5$)$_2$(SO$_4$)$_2$. On cooling and at zero magnetic field this compound enters a one-dimensional regime with short-range magnetic correlations, marked by a broad maximum in the specific heat and magnetic susceptibility at $T_\mathrm{max}\sim 2\,\mathrm{K}$, followed by an ordered antiferromagnetic phase below $T_\mathrm{N}\sim 1\,\mathrm{K}$ induced by small interchain couplings. The intermediate-temperate one-dimensional regime can be modeled using exact quantum-transfer-matrix calculations, which perfectly describe the nonmonotonic behavior of T_max as a function of the magnetic field, giving $J = 4.25\,\mathrm{K}$ for the intrachain exchange parameter. The analysis of magnetic specific-heat and susceptibility data at low temperature indicates that the interchain exchange couplings are an order of magnitude smaller than the coupling inside the chains.