A Basis for Lanthanide Single-Molecule Magnets

Abstract

The basic information on lanthanide single-molecule magnets (SMMs) has been introduced systematically in this chapter covering the magnetism of lanthanide, the characterization and relaxation dynamics of SMMs, and advanced means of studying lanthanide SMMs. In particular, the brief introduction to the single-crystal magnetic measurements and ab initio calculations of lanthanide SMMs demonstrate the up-to-date progresses on elucidating the magnetic anisotropy and relaxation mechanism of highly anisotropic lanthanide SMMs. Such basic knowledge is very essential for the readers to grasp the subject of this book. Keywords Single-molecule magnet · Lanthanide ions · Magnetic anisotropy · Relaxation dynamics · Ab initio calculationsThis chapter will provide a basis for lanthanide single-molecule magnets [1, 2] (SMMs) ranging from the magnetism of lanthanide and the magnetic relaxation theory to advanced means for characterizing SMMs. We believe this basis is very essential for the readers to grasp the subject of this book. In 2011, Long et al. depicted the requisite electronic structure for a lanthanide complex to exhibit single-molecule magnetic behavior by applying a simple model [3]. Herein, the free-ion and crystal-field contributions to the 4f electronic structure are highlighted. Considering the complexity and specialty of the 4f-element electronic structure, we will introduce the magnetic properties of lanthanide ions in the first section of this chapter. The second part focuses on the characterization and relaxation dynamics of SMMs, which is a foundation for understanding and grasping this field for new and current researchers. Finally, lanthanide SMMs are discussed with an emphasis on the specialty in contrast to transition metal SMMs, especially the advanced means, such as angle-resolved magnetometry and ab initio calculations, which can provide a direct detection for the relationship between the crystal structure and magnetic properties, are introduced.

The rise of 3-d single-ion magnets in molecular magnetism: towards materials from molecules?

“…As a result the authors were able to rule out phonon bottlenecks and transverse anisotropy respectively, as the causes of the observed slow relaxation. Instead, they suggest that an optical/acoustic Raman process is responsible for the spin relaxation, since the relaxation time ( τ –1 ) for the complex can be fitted to a T – n law 10. This yields a best-fit n = 4.5.…”

“…It is these additional relaxation pathways (Fig. 2) that cause experimentally observed deviations from linearity in Arrhenius plots 10. Specifically, there are three types of spin-lattice relaxation mechanism: (i) direct processes involve relaxation from – M s to + M s with emission of a single lattice phonon (ii) an Orbach process involves absorption of a phonon followed by phonon emission and relaxation from an excited state whereas (iii) a Raman process, is analogous to the Orbach mechanism with the exception that the relaxation occurs from a virtual state.…”

Molecular single-ion magnets based on lanthanides and actinides: Design considerations and new advances in the context of quantum technologies

“…The loop width generally increases with a decrease of temperature and with an increase of the field-charging rate [32]. The most used method for detecting and characterising slow magnetic relaxation is through the use of alternating current (ac) magnetic susceptibility measurements [65][66][67][68][69][70]. Wherein, a small oscillating magnetic field is applied to the sample, and the in-phase and out-of-phase components of magnetic susceptibility are measured over a range of temperatures, oscillation frequencies, and static magnetic fields.…”

Two-color thermosensors based on [Y $$_{1-x}$$ 1 - x Dy $$_x$$ x (acetylacetonate) $$_3$$ 3 (1,10-phenanthroline)] molecular crystals

“…This energy transfer is typically radiationless and can occur via several possible mechanisms: electron exchange [48,53], dipole-dipole interactions (both allowed [62][63][64][65] and unallowed transitions [48,66]), dipole-quadrapole interactions [48], and excitons [67,68] This energy transfer has been empirically found to be most efficient if the ligand's lowest triplet energy level is between 0.23 eV and 0.62 eV greater than the lanthanide's primary luminescent state, as energy back-transfer is more likely to occur for energy differences of < 0.23 eV [51,69]. One such material, satisfying this criterion is [Dy(acetylacetonate) 3 (1,10-phenanthroline)] ([Dy(acac) 3 (phen)]) [52,[70][71][72][73], which is the subject material of this study. To demonstrate the energy level spacing of the ligands and Dy ion we provide a simplified energy level diagram in Figure 1 where the energy levels are taken from the literature [45,47,52,74,75].…”

“…This means that during excitation the primary absorption is due to the acac ligand, which can then nonradiatively transition to the lowest triplet state T 1 (energy ≈ 3.134 eV) via intersystem crossing. [70,71], a phosphor for white OLEDs [72,73], and a NIR optical phosphor for use in telecommunications [52]. In these previous studies the authors prepared the material with a Dy concentration of 100 mol%, while in our study we dilute [Dy(acac) 3 3 (phen)] MCs we use X-ray diffraction (XRD) with a Cu-Kα radiation source (λ=1.5418Å) operated at 40 kV and 40 mA.…”