Ferromagnetic coupling and magnetic anisotropy in molecular Ni(II) squares

TL;DR

This study explores the magnetic properties of two Ni(II) molecular complexes, revealing weak ferromagnetic coupling and significant anisotropy, with differences in zero-field-splitting parameters attributed to structural factors.

Contribution

It provides detailed analysis of magnetic coupling and anisotropy in Ni(II) squares using magnetometry and effective spin Hamiltonian modeling, highlighting differences in zero-field-splitting.

Findings

Weak ferromagnetic coupling in both compounds

Significant easy-axis anisotropy observed

Differences in zero-field-splitting parameters explained by structural factors

Abstract

We investigated the magnetic properties of two isostructural Ni(II) metal complexes [Ni4Lb8] and [Ni4Lc8]. In each molecule the four Ni(II) centers form almost perfect regular squares. Magnetic coupling and anisotropy of single crystals were examined by magnetization measurements and in particular by high-field torque magnetometry at low temperatures. The data were analyzed in terms of an effective spin Hamiltonian appropriate for Ni(II) centers. For both compounds, we found a weak intramolecular ferromagnetic coupling of the four Ni(II) spins and sizable single-ion anisotropies of the easy-axis type. The coupling strengths are roughly identical for both compounds, whereas the zero-field-splitting parameters are significantly different. Possible reasons for this observation are discussed.