Tight-Binding Approach to Pyrazine-Mediated Superexchange in Copper–Pyrazine Antiferromagnets

Abstract

We investigate the cause of spatial superexchange anisotropy in a family of copper-based, quasi-two-dimensional materials with very similar geometries. The compounds in this family differ mainly in their inter-layer separation but they have very different magnetic interactions, even within the basal plane. We use density functional theory and Wannier functions to parameterize two complimentary tight-binding models and show that the superexchange between the Cu2+ ions is dominated by a σ-mediated interaction between hybrid Cu–pyrazine orbitals centered on the copper atoms. We find no correlations between the strength of this exchange interaction and homologous geometric features across the compounds, such as Cu and pyrazine bond lengths and orientations of nearby counterions. We find that the pyrazine tilt angles do not affect the Cu–pyrazine–Cu exchange because the lowest unoccupied molecular orbital on pyrazine is at a very high energy (relative to the frontier orbitals, which are Cu-based). We conclude that careful control of the entire crystal structure, including non-homologous geometric features such as the inter-layer organic ligands, is vital for engineering magnetic properties.

Anomalous magnetic exchange in a dimerized quantum magnet composed of unlike spin species

“…Both Cu-and V-centered orbitals lie perpendicular to the dimers and therefore the overlap between orbitals on adjacent dimers within the bc plane is much stronger than the overlap between orbitals along the dimer. We note that a similar tight-binding model based on Wannier orbitals was able to describe the magnetic interactions in copper-pyrazine antiferromagnets [45]. However, in those systems superexchange is mediated by pyz ligands lying in the JT plane, with the shapes of the Wannier orbitals reflecting this.…”

A Ballistic Transport Nanodevice Based on Graphene Nanoribbon FET by Enhanced Productivity for Both Low-Voltage and Radio-Frequency Scopes

“…In order to accurately analyze the electrical performance of the proposed ultrascale GNRFET, it is essential to describe the atomic description of band structures by the tight-binding (TB) approach. 9,20,21 After a description of band structure, the NEGF method coupled by Schrodinger equation under the non-equilibrium condition is solved in a self-consistent manner by Poisson equation in order to measure the electron transport for the device. In order to save the computational time along with high accuracy, 2D GNR split up into a set of 1D subbands due to structural confinement in transverse direction.…”