One of the holy grails in the area of single-molecule magnets (SMMs) is to achieve control over microscopic spin Hamiltonian parameters of molecules, and this is generally achieved via chemical intuition, serendipity, and occasionally using external stimuli such as pressure. Among the spin Hamiltonian parameters that control the performance of SMMs, magnetic exchange coupling and magnetic anisotropy are the key parameters that can be controlled via chemical design, which is challengingactive space self-consistent. In this work, we have explored using a combination of density functional theory (DFT) and ab initio CASSCF/RASSI-SO method in combination with the response theory method wherein an external electric field was applied to effect controlled geometric changes that, in turn, were found to alter both the magnetic exchange and magnetic anisotropy in a {Ln-Cr} (Ln= GdIII and DyIII) molecule. Particularly, here we studied [CrF2(py)4]Ln(hfac)4] (Ln = Gd (1) and DyIII (2)) molecule possessing antiferromagnetic coupling between GdIII…CrIII using an oriented external electric field, and our study reveals that application of field 0.4 to 2 V/Å along the Cr–F and Gd–F directions alter the geometry, and this, in turn, alters the J and the associated magnetic anisotropy. As this J is weakly antiferromagnetic, our aim was to apply electric field to reduce the anti-ferromagnetic coupling and see if it is possible to alter the magnitude of magnetic coupling. Applying an oriented external electric field (OEEF) along the ± x-axis led to significant elongation of the Gd−F bond distance, increasing from 2.349 Å in the absence of a field to 2.864 Å at ± 2 V/Å. This structural modification resulted in a notable reduction of the antiferromagnetic J, decreasing from −0.960 cm−1 in the ground state of 1 to −0.100 cm−1 at +2 V/Å, corresponding to an approximate 90% decrease. Conversely, applying the OEEF along the ± z-axis induced negligible changes in both the Gd−F bond distance and the exchange coupling constant. Although the sign change was not achieved, this suggests a viable way to alter the magnetic exchange. For the corresponding DyIII analogues, our calculations indicate that the corresponding geometrical distortions, particularly shorter Dy-F distance at the applied field strength of 0.4 to 2 V/Å, enhance the magnetic anisotropy and eventually yield better performing SMMs. These findings align with experimental observations reported in the literature, where electric fields have been shown to modulate magnetic exchange interactions in molecular systems. Our results demonstrate the potential of using external electric fields to tailor magnetic properties in {3d–4f} complexes, thereby advancing the design of materials with controllable magnetic behaviours. Graphical Abstract External electric fields are explored as a novel tool to modulate magnetic exchange interactions and magnetic anisotropy in {3d–4f} complexes, offering a new avenue to control molecular magnetic properties via structural distortions. This study paves the way for designing materials with tuneable magnetic behaviours using external stimuli.

Modulating magnetic exchange and magnetic anisotropy in {3d–4f} complexes using external electric field

期刊论文
发表日期：

2025年12月2日

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Tanu Sharma,
Gopalan Rajaraman

摘要

One of the holy grails in the area of single-molecule magnets (SMMs) is to achieve control over microscopic spin Hamiltonian parameters of molecules, and this is generally achieved via chemical intuition, serendipity, and occasionally using external stimuli such as pressure. Among the spin Hamiltonian parameters that control the performance of SMMs, magnetic exchange coupling and magnetic anisotropy are the key parameters that can be controlled via chemical design, which is challengingactive space self-consistent. In this work, we have explored using a combination of density functional theory (DFT) and ab initio CASSCF/RASSI-SO method in combination with the response theory method wherein an external electric field was applied to effect controlled geometric changes that, in turn, were found to alter both the magnetic exchange and magnetic anisotropy in a {Ln-Cr} (Ln= Gd^III and Dy^III) molecule. Particularly, here we studied [CrF₂(py)₄]Ln(hfac)₄] (Ln = Gd (1) and Dy^III (2)) molecule possessing antiferromagnetic coupling between Gd^III…Cr^III using an oriented external electric field, and our study reveals that application of field 0.4 to 2 V/Å along the Cr–F and Gd–F directions alter the geometry, and this, in turn, alters the J and the associated magnetic anisotropy. As this J is weakly antiferromagnetic, our aim was to apply electric field to reduce the anti-ferromagnetic coupling and see if it is possible to alter the magnitude of magnetic coupling. Applying an oriented external electric field (OEEF) along the ± x-axis led to significant elongation of the Gd−F bond distance, increasing from 2.349 Å in the absence of a field to 2.864 Å at ± 2 V/Å. This structural modification resulted in a notable reduction of the antiferromagnetic J, decreasing from −0.960 cm⁻¹ in the ground state of 1 to −0.100 cm⁻¹ at +2 V/Å, corresponding to an approximate 90% decrease. Conversely, applying the OEEF along the ± z-axis induced negligible changes in both the Gd−F bond distance and the exchange coupling constant. Although the sign change was not achieved, this suggests a viable way to alter the magnetic exchange. For the corresponding Dy^III analogues, our calculations indicate that the corresponding geometrical distortions, particularly shorter Dy-F distance at the applied field strength of 0.4 to 2 V/Å, enhance the magnetic anisotropy and eventually yield better performing SMMs. These findings align with experimental observations reported in the literature, where electric fields have been shown to modulate magnetic exchange interactions in molecular systems. Our results demonstrate the potential of using external electric fields to tailor magnetic properties in {3d–4f} complexes, thereby advancing the design of materials with controllable magnetic behaviours.

Graphical Abstract

External electric fields are explored as a novel tool to modulate magnetic exchange interactions and magnetic anisotropy in {3d–4f} complexes, offering a new avenue to control molecular magnetic properties via structural distortions. This study paves the way for designing materials with tuneable magnetic behaviours using external stimuli.