Exchange parameters of copper-based quasi-two-dimensional Heisenberg magnets measured using high magnetic fields and muon-spin rotation

TL;DR

This study combines pulsed-field magnetization and muon-spin rotation to accurately measure exchange parameters in copper-based 2D Heisenberg magnets, revealing the relationship between molecular structure and magnetic interactions.

Contribution

It provides a quantitative method to determine in-plane and interlayer exchange energies in Cu-based 2D magnets using high magnetic fields and muon-spin rotation data.

Findings

Monte-Carlo simulations accurately reproduce magnetization data

The critical field $B_c$ measures the in-plane exchange energy $J$

Structural tilting influences the exchange interactions

Abstract

Pulsed-field magnetization experiments (fields $B$ of up to 85 T and temperatures $T$ down to 0.4 K) are reported on nine organic Cu-based two-dimensional (2D) Heisenberg magnets. All compounds show a low-$T$ magnetization that is concave as a function of $B$, with a sharp ``elbow'' transition to a constant value at a field $B_{\rm c}$. Monte-Carlo simulations including a finite interlayer exchange energy $J_{\perp}$ quantitatively reproduce the data; the concavity indicates the effective dimensionality and $B_{\rm c}$ is an accurate measure of the in-plane exchange energy $J$. Using these values and Ne\'el temperatures measured by muon-spin rotation, it is also possible to obtain a quantitative estimate of $|J_{\perp}/J|$. In the light of these results, it is suggested that in magnets of the form [Cu(HF$_2$)(pyz)$_2$]X, where X is an anion, the sizes of $J$ and $J_{\perp}$ are controlled by the tilting of the pyrazine (pyz) molecule with respect to the 2D planes.