Single-ion magnetism in the extended solid-state: insights from X-ray absorption and emission spectroscopy.
AuthorsHuzan, Myron S; orcid: 0000-0002-6238-3735
Mosselmans, J Frederick W; orcid: 0000-0001-6473-2743
Breitner, Franziska A
Gee, Leland B; orcid: 0000-0002-5817-3997
Titus, Charles J; orcid: 0000-0001-6312-8552
Baker, Michael L; orcid: 0000-0002-8246-3177
MetadataShow full item record
AbstractLarge single-ion magnetic anisotropy is observed in lithium nitride doped with iron. The iron sites are two-coordinate, putting iron doped lithium nitride amongst a growing number of two coordinate transition metal single-ion magnets (SIMs). Uniquely, the relaxation times to magnetisation reversal are over two orders of magnitude longer in iron doped lithium nitride than other 3d-metal SIMs, and comparable with high-performance lanthanide-based SIMs. To understand the origin of these enhanced magnetic properties a detailed characterisation of electronic structure is presented. Access to dopant electronic structure calls for atomic specific techniques, hence a combination of detailed single-crystal X-ray absorption and emission spectroscopies are applied. Together K-edge, L<sub>2,3</sub>-edge and Kβ X-ray spectroscopies probe local geometry and electronic structure, identifying iron doped lithium nitride to be a prototype, solid-state SIM, clean of stoichiometric vacancies where Fe lattice sites are geometrically equivalent. Extended X-ray absorption fine structure and angular dependent single-crystal X-ray absorption near edge spectroscopy measurements determine Fe<sup>I</sup> dopant ions to be linearly coordinated, occupying a <i>D</i> <sub>6h</sub> symmetry pocket. The dopant engages in strong 3dπ-bonding, resulting in an exceptionally short Fe-N bond length (1.873(7) Å) and rigorous linearity. It is proposed that this structure protects dopant sites from Renner-Teller vibronic coupling and pseudo Jahn-Teller distortions, enhancing magnetic properties with respect to molecular-based linear complexes. The Fe ligand field is quantified by L<sub>2,3</sub>-edge XAS from which the energy reduction of 3d <sub><i>z</i> <sup>2</sup></sub> due to strong 4s mixing is deduced. Quantification of magnetic anisotropy barriers in low concentration dopant sites is inhibited by many established methods, including far-infrared and neutron scattering. We deduce variable temperature L<sub>3</sub>-edge XAS can be applied to quantify the <i>J</i> = 7/2 magnetic anisotropy barrier, 34.80 meV (∼280 cm<sup>-1</sup>), that corresponds with Orbach relaxation <i>via</i> the first excited, <i>M</i> <sub>J</sub> = ±5/2 doublet. The results demonstrate that dopant sites within solid-state host lattices could offer a viable alternative to rare-earth bulk magnets and high-performance SIMs, where the host matrix can be tailored to impose high symmetry and control lattice induced relaxation effects.
CitationChemical science, volume 11, issue 43, page 11801-11810
DescriptionFrom Europe PMC via Jisc Publications Router
History: ppub 2020-10-01, epub 2020-10-07
Publication status: Published
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