Isotope effect in quasi-two-dimensional metal-organic antiferromagnets

TL;DR

This study demonstrates that isotopic substitution in quasi-two-dimensional organic antiferromagnets causes measurable shifts in magnetic transition temperatures and fields, revealing a link between isotopic effects and magnetic properties in layered materials.

Contribution

It provides the first experimental evidence of isotope effects on magnetic properties in Q2D antiferromagnets, highlighting the role of hydrogen bonds in mediating superexchange interactions.

Findings

Neel temperature shifts by approximately 4% with isotopic substitution.

Critical magnetic fields change by about 4% due to isotope effects.

Exchange energies are affected by hydrogen versus deuterium substitution.

Abstract

Although the isotope effect in superconducting materials is well-documented, changes in the magnetic properties of antiferromagnets due to isotopic substitution are seldom discussed and remain poorly understood. This is perhaps surprising given the possible link between the quasi-two-dimensional (Q2D) antiferromagnetic and superconducting phases of the layered cuprates. Here we report the experimental observation of shifts in the N\'{e}el temperature and critical magnetic fields ($\Delta T_{\rm N}/T_{\rm N}\approx 4%$; $\Delta B_{\rm c}/B_{\rm c}\approx 4%$) in a Q2D organic molecular antiferromagnets on substitution of hydrogen for deuterium. These compounds are characterized by strong hydrogen bonds through which the dominant superexchange is mediated. We evaluate how the in-plane and inter-plane exchange energies evolve as the hydrogens on different ligands are substituted, and suggest a possible mechanism for this effect in terms of the relative exchange efficiency of hydrogen and deuterium bonds.