Electronic structure and magnetic anisotropy for nickel-based molecular magnets

TL;DR

This study uses density-functional theory to analyze the electronic structure and magnetic anisotropy of nickel-based molecular magnets, aiming to explain experimental magnetic phenomena such as exchange bias and EPR anomalies.

Contribution

It provides detailed theoretical calculations of electronic and magnetic properties for Ni4 molecules with different ligands, highlighting discrepancies with experimental spin states.

Findings

Calculated magnetic anisotropy barriers of 4-6 K.

Total spin of the lowest-energy state is S=0, contrary to experimental results.

Electronic structure insights into ligand effects on magnetic properties.

Abstract

Recent magnetic measurements on tetra-nickel molecular magnets [Ni(hmp)(ROH)Cl]$_4$, where R=CH$_3$, CH$_2$CH$_3$, or (CH$_2$)$_2$C(CH$_3$)$_3$ and hmp$^-$ is the monoanion of 2-hydroxymethylpyridine, revealed a strong exchange bias prior to the external magnetic field reversal as well as anomalies in electron paramagnetic resonance peaks at low temperatures. To understand the exchange bias and observed anomalies, we calculate the electronic structure and magnetic properties for the Ni$_4$ molecules with the three different ligands, employing density-functional theory. Considering the optimized structure with possible collinear spin configurations, we determine a total spin of the lowest-energy state to be S=0, which does not agree with experiment. We also calculate magnetic anisotropy barriers for all three types of Ni$_4$ molecules to be in the range of 4-6 K.