Spin-specific heat determination of the ratio of competing first- and second-neighbor exchange interactions in frustrated spin-$\frac{1}{2}$ chains

TL;DR

This paper demonstrates that spin specific heat measurements can uniquely determine the ratio of competing exchange interactions in frustrated spin-1/2 chains, resolving ambiguities from magnetic susceptibility data.

Contribution

It introduces a method to determine the ratio J2/|J1| using spin specific heat, providing a new tool for analyzing frustrated magnetic chains.

Findings

Spin specific heat directly determines the exchange ratio.

The method resolves ambiguities in magnetic susceptibility analysis.

Application to LiCuSbO4 confirms the effectiveness of the approach.

Abstract

The magnetic susceptibility $\chi(T)$ of spin-1/2 chains is widely used to quantify exchange interactions, even though $\chi(T)$ is similar for different combinations of ferromagnetic $J_1$ between first neighbors and antiferromagnetic $J_2$ between second neighbors. We point out that the spin specific heat $C(T)$ directly determines the ratio $\alpha = J_2/|J_1|$ of competing interactions. The $J_1-J_2$ model is used to fit the isothermal magnetization $M(T,H)$ and $C(T,H)$ of spin-1/2 Cu(II) chains in LiCuSbO$_4$. By fixing $\alpha$, $C(T)$ resolves the offsetting $J_1$, $\alpha$ combinations obtained from $M(T,H)$ in cuprates with frustrated spin chains.