Understanding the Magnetic Anisotropy toward Single-Ion Magnets

Abstract

Single-molecule magnets (SMMs) can retain their magnetization status preferentially after removal of the magnetic field below a certain temperature. The unique property, magnetic bistable status, enables the molecule-scale SMM to become the next-generation high-density information storage medium. SMMs' new applications are also involved in high-speed quantum computation and molecular spintronics. The development of coordination chemistry, especially in transition metal (3d) and lanthanide (4f) complexes, diversifies SMMs by introducing new ones. In both 3d and 4f SMMs, the ligands play a fundamental role in determining the SMMs' magnetic properties. The strategies for rationally designing and synthesizing high-performance SMMs require a comprehensive understanding of the effects of a crystal field. In this Account, we focus mainly on the magneto-structural correlations of 4f or 3d single-ion magnets (SIMs), within which there is only one spin carrier. These one-spin carrier complexes benefit from getting rid of exchange interactions and relatively large distances of magnetic centers in the lattice, providing the ease to construct high-performance SIMs from the crystal field perspective. We will briefly introduce the crystal field approach for 4f or 3d complexes and then the magnetic anisotropy analysis via the displaced-charge electrostatic model. This idea has been proposed for years, and the related work is also highlighted. The angular-resolved magnetometry method, predominating in determining the magnetic anisotropic axes direction, is discussed. We also give a brief introduction of the quantum chemistry ab initio method, which has shown to be powerful in understanding the magnetic anisotropy and low-lying states. In the constructing and characterizing part, we give an overview of the SIMs based on lanthanide and transition ions, reported by our group in the past 5 years. In the 4f-SIMs survey, we discuss how β-diketonates and cyclomultienes, and their combination, as ligands to influence magnetic anisotropy and provide some suggestion on designing SIMs based on different lanthanide ions. In the 3d-SIMs survey, we fully discuss the correlation between zero-field-splitting parameter D and molecular geometrical angle parameters. Finally, we lay out the challenges and further development of SIMs. We hope the understanding we provide about single-ion magnetic properties will be helpful to design high-performance SMMs.

Mononuclear Dysprosium(III) Complexes with Triphenylphosphine Oxide Ligands: Controlling the Coordination Environment and Magnetic Anisotropy

“…This ligand field is better suited for the prolate Er III ion, as for the Dy III ion, this configuration dramatically reduces the ground-first excited state gap (7 cm −1 , see Table 1) compared to 1. As expected for the hard-plane anisotropy, the g xx , g yy axes are found to point along the {Dy(O-P) 4 } plane, while the g zz axial direction lies along the two (NO 3 ) − ligands (Figure 5b).…”

“…Complexes that exhibit this behavior have been termed single-molecule magnets it is possible to isolate several different coordination complexes, each with a unique coordination environment using the TPPO ligand ( Figure 1). FeCl 3 was used in the synthesis of 5 in order to isolate a further unique coordination environment, this being the previously reported [Dy III (OPPh 3 ) 5 Cl](FeCl 4 ) 2 complex reported by Wang and co-workers [18], however, the product of 5 differed from that reported, resulting in a first coordination sphere identical to that of 4, with four TPPO ligands and two chloride ions-[Dy III (OPPh 3 ) 4 Cl 2 ](FeCl 4 ) (5).…”

“…The χ M T products decrease gradually for 1-5 as the temperature is reduced from 300 K to 12.11, 5.56, 5.00, 5.03 and 9.98 cm 3 ·mol −1 ·K at 2 K in a field of 1 T. (1)(2)(3)(4), with the value for 5 consistent with the presence of a Dy III ion and a non-coordinated {Fe III Cl 4 } − counterion (3d 5 , g = 2, χ M T = 4.375 cm 3 ·mol −1 ·K). The χ M T products are found to decrease upon reducing the temperature for 1-5, which is attributed to depopulation of the m J levels arising from the crystal field levels.…”

“…4 Cl 2 ](FeCl 4 ) (5). These complexes are characterized using single crystal X-ray diffraction, which revealed that each complex has a unique coordination environment around the Dy III ion, which results in varying dynamic magnetic behavior.…”

Field-Induced Slow Magnetic Relaxation of Mono- and Dinuclear Dysprosium(III) Complexes Coordinated by a Chloranilate with Different Resonance Forms

“…Molecule-based nanomagnets, such as single-molecule magnets (SMMs) [1][2][3][4][5][6][7] and single-ion magnets (SIMs) [8][9][10][11][12], are strictly low-dimensional magnetic systems that exhibit magnetization blocking at low temperatures, quantum tunneling of magnetization (QTM) [13], and quantum coherence [14,15]. Accordingly, SMMs have attracted a great deal of interest as promising candidates blocking at low temperatures, quantum tunneling of magnetization (QTM) [13], and quantum coherence [14,15].…”