α-Cobalt Hydroxides as 2D Magnets: Tuning Magnetism through Exchange Interactions

Abstract

In this work, we present a microscopic analysis of the magnetic properties of the α-CoII layered hydroxide (LHs) family. Using first-principles molecular dynamics complemented by DFT+U calculations and Monte Carlo simulations, we provide a detailed magnetic characterization of the previously reported hybrid α-CoII LHs ( Chem. Eur. J. 2021, 27, 921−927). By parametrizing Heisenberg-type Hamiltonians, we demonstrate that interlayer magnetic interactions are significantly weaker than intralayer ones and even smaller than the thermal energies involved in typical experiments. This indicates that the magnetic behavior of these systems is primarily governed by intralayer interactions, effectively rendering them two-dimensional magnets. Monte Carlo simulations allow us to estimate the relevant macroscopic magnetic variables, yielding excellent agreement with our previously reported experimental data. Extending the analysis to different coordination ligands, we find that variations in the magnetic properties of α-CoII LHs are mainly driven by local distortions in the tetrahedral Co(II) environment, which directly modulate the superexchange interaction between tetrahedral and octahedral Co(II) ions. For the hybrid α-CoII LHs, these distortions are closely linked to the specific orientation of the organic molecules within the interlayer region, suggesting that a controlled molecular arrangement can be exploited as a form of molecular engineering to tailor the magnetic response of LHs. Our findings support the formulation of a simplified model that captures the essential magnetic physics of these compounds, based on the modulation of intralayer exchange interactions. These insights pave the way toward the design of layered materials with tunable magnetic properties and underscores their potential as adaptable platforms for future spintronics applications.