Abstract
Single-molecule magnets represent a promising route to achieve potential applications such as high-density information storage and spintronics devices. Among others, 4d/5d elements such as Re(IV) ion are found to exhibit very large magnetic anisotropy, and inclusion of this ion-aggregated clusters yields several attractive molecular magnets. Here, using ab intio calculations, we unravel the source of giant magnetic anisotropy associated with the Re(IV) ions by studying a series of mononuclear Re(IV) six coordinate complexes. The low-lying doublet states are found to be responsible for large magnetic anisotropy and the sign of the axial zero-field splitting parameter (D) can be categorically predicted based on the position of the ligand coordination. Large transverse anisotropy along with large hyperfine interactions opens up multiple relaxation channels leading to a fast quantum tunnelling of the magnetization (QTM) process. Enhancing the Re-ligand covalency is found to significantly quench the QTM process.
Highlights
Single-molecule magnets represent a promising route to achieve potential applications such as high-density information storage and spintronics devices
Owing to inherently large magnetic anisotropy, lanthanide-based complexes are promising candidate for single-ion magnets[2,3,5,12,13,14,15,16,17] and mononuclear SMMs based on transition metal ions are relatively scarce in the literature, as stronger ligand field interactions suppress the orbital contributions to the anisotropy and the barrier heights (Ueff)[18,19,20,21,22,23,24,25]
By modelling structurally diverse 13 mononuclear six coordinate Re(IV) complexes[39,41,43,44,45,46,47,48,49,50,51], we aim to answer the following intriguing questions (i) What is the suitable theoretical methodology to compute ZFS parameters in 5d transition metal ions such as Re(IV) complexes? (ii) What is the origin of giant D values and is there a correlation between the nature of the donor atoms and the sign of the D values in these complexes? (iii) What is mechanism of magnetic relaxation in Re(IV) singleion magnets and how this is influenced by the metal–ligand covalency?
Summary
Single-molecule magnets represent a promising route to achieve potential applications such as high-density information storage and spintronics devices. In the past few years, late-transition metal ions have gained much attention in the area of SMMs. The diffused magnetic orbitals of the 4d/5d ions translate stronger magnetic exchange, whereas larger spin-orbit coupling constants (SOCs) exhibited by these ions[26], often lead to highly anisotropic ground state (highly anisotropic g-tensors with an unusually large zero-field splitting values (ZFS)). The diffused magnetic orbitals of the 4d/5d ions translate stronger magnetic exchange, whereas larger spin-orbit coupling constants (SOCs) exhibited by these ions[26], often lead to highly anisotropic ground state (highly anisotropic g-tensors with an unusually large zero-field splitting values (ZFS)) These two essential conditions along with a possibility of exhibiting anisotropic/anti-symmetric exchange makes this class of molecules ideal for observing SMM behaviour[27,28,29,30,31,32,33]. By modelling structurally diverse 13 mononuclear six coordinate Re(IV) complexes[39,41,43,44,45,46,47,48,49,50,51], we aim to answer the following intriguing questions (i) What is the suitable theoretical methodology to compute ZFS parameters in 5d transition metal ions such as Re(IV) complexes? (ii) What is the origin of giant D values and is there a correlation between the nature of the donor atoms and the sign of the D values in these complexes? (iii) What is mechanism of magnetic relaxation in Re(IV) singleion magnets and how this is influenced by the metal–ligand covalency?
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