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Nanostructured Hybrid Magnetic Materials
Published in Ram K. Gupta, Sanjay R. Mishra, Tuan Anh Nguyen, Fundamentals of Low Dimensional Magnets, 2023
Single-molecule magnets represent the smallest bistable magnetic systems, which makes them ideal candidates for quantum computation. However, the thermal spin fluctuations usually lead to random magnetization at room temperature. The magnetic coupling between the molecule and FMs has a significant influence on the magnetization ordering. The magnetic exchange by coupling the SMM with FM could significantly affect the magnetization within the interface. Therefore, the deposition of molecular magnets on FMs may provide an effective solution to manipulate the magnetization in a controllable way. Wende et al. [40] observed ordered molecular structure and magnetization for octaethylporphyrin Fe(III) chloride (OEP) on 5 ML Ni/Cu(100) surface. The Fe and Ni atoms show identical hysteresis loops. These results demonstrated that a ferromagnetic exchange coupling exists between the Fe moments in the porphyrin molecules and the magnetic substrate.
Low Temperature Investigation of Magnetic Molecules by Scanning Probe Microscopies
Published in Klaus D. Sattler, st Century Nanoscience – A Handbook, 2020
Giulia Serrano, Matteo Mannini, Luigi Malavolti, Michele Serri
An interesting class of molecules is represented by single-molecule magnets (SMMs). This fascinating family of molecular complexes features, at low temperature, magnetic bistability that is characteristic of the individual molecule and manifests as magnetic hysteresis loops (Gatteschi et al. 2006). The SMM properties usually originate from a giant spin, resulting from the presence of (super-)exchange-coupled magnetic ions, and an easy axis of magnetic anisotropy defining two preferable orientations of the magnetic moment. Recently, a similar behavior has also been obtained using single ion systems achieving the manifestation of SMM behavior at unprecedented temperatures (Ishikawa 2007; Goodwin et al. 2017). In all SMMs, reversal of the magnetization can be thermally activated, overcoming the barrier between the two lower energy states, or, in specific resonance conditions, by a quantum tunneling process (Quantum Tunneling of the Magnetization, QTM). The former mechanism is predominant above the so-called blocking temperature of the system, while the latter is responsible for the relaxation of the magnetization also observed at low temperature, for example when, in zero magnetic field, the two low-energy states are degenerate. By applying a magnetic field along the easy axis of magnetization, the spin levels are shifted according to the Zeeman interaction and different tunneling paths are activated or made inactive. This leads to the observation of a stepped magnetization hysteresis loop below the blocking temperature, as it was demonstrated in ensembles of SMMs such as single crystals (Sangregorio et al. 1997) or mono-layers of well-ordered molecules (Mannini et al. 2010). Early experiments addressing individual molecules have opened fascinating perspectives for developing devices that profit from both magnetic bistability and quantum features (Urdampilleta et al. 2011; Thiele et al. 2014).
Synthesis, characterization and magnetic studies of dinuclear lanthanide complexes constructed with a Schiff base ligand
Published in Journal of Coordination Chemistry, 2020
Amin Khan, Olaf Fuhr, Muhammad Nadeem Akhtar, Yanhua Lan, Madhu Thomas, Annie K. Powell
Single molecule magnets (SMMs) in the field of research are attractive for both physicists and chemists because of their promising applications in high-density information storage, molecular spintronics and quantum computing [1, 2]. Large negative axial magnetic anisotropy (D) and high spin values (S) are fundamental requirements and useful to increase the anisotropic energy barrier (Ueff) to reversal of the molecular magnetization [3]. Recently, attention has been diverted to lanthanide systems due to the significant magnetic anisotropy of lanthanide ions arising from their large, unquenched orbital angular momentum [4]. The significance of homonuclear lanthanide complexes in molecular magnetism has increased with the discovery of the {Dy5} [5] and {Dy4K2} [6] complexes which display the highest barriers of energy for reversal of magnetization in any system so far. Up to now, various nuclearity lanthanide clusters have been reported [7–11] but proper ligand design system to synthesis polynuclear Ln(III) complexes with interesting properties is still a synthetic challenge.
Synthesis and characterization of some novel Mn(III) glycinato complexes with catalytic applications
Published in Journal of Coordination Chemistry, 2019
Mn(III) complexes have important roles in chemical and biological catalysis [1–5]. (Salen) Mn(III) complexes have been used for preparation of chiral epoxides and sulphoxides, both of which are important chiral synthons in organic chemistry [3, 5]. Mn(III) complexes have been used as catalysts for alcohol oxidation in the presence of H2O2 [6] and olefin oxygenation to alcohol in the presence of NaBH4 [7]. Zeolite-Y enslaved manganese(III) complexes have been used as heterogeneous catalysts [8]. A Mn(III) porphyrin complex anchored onto multiwalled carbon nanotubes have been used as efficient and reusable catalysts for heterogeneous reduction of aldehyde and ketones [9]. Mn(III) has been found to play an important role at the redox centers of biological systems; important among those are catalase, superoxide dismutase, ribonucleotide reductase, and the oxygen evolving center of photosystem II (PS-II) [10]. Attempts have been made to mimic the active site of these enzymes [11–13]. Membrane permeable Mn(III) complexes for molecular magnetic resonance imaging of intracellular targets have been synthesized [14]. A number of Mn(III) complexes with special magnetic properties have been prepared and characterized [15–18]. Important among these are preparations of compounds having single molecule magnet properties [18]. The potential applications of single molecule magnets [SMMs] include information processing, data storage, quantum computing, spintronics, and biomedical applications [19, 20].
A new β-diketonate Dy(III) single‒ion magnet featuring multiple magnetic relaxation processes
Published in Journal of Coordination Chemistry, 2018
Peipei Cen, Xiufang Ma, Xiangyu Liu, Yi-Quan Zhang, Gang Xie, Sanping Chen
Single-molecule magnets (SMMs) have been a hot topic in molecular magnetism due to their potential applications in high density information storage, quantum computing, spintronics devices [1], and magnetic refrigeration [2]. Because of the strong spin-orbital coupling effect and significant magnetic anisotropies of lanthanide ions [3], a number of lanthanide-containing SMMs, including d–f and pure f-based polynuclear SMMs [4], have been explored and display SMM behavior with superior effective energy barriers (Ueff) and blocking temperatures (TB) [5]. Notably, the Dy(III) ion was widely employed to design a number of SMMs with mononuclear, multinuclear and chain structures owing to its large magnetic moment with a Kramers ground state of 6H15/2 and large Ising-type magnetic anisotropy [6]. Thereinto, the exploitation of monometallic Dy(III)-containing molecular magnets or so-called single-ion magnets (SIMs) is especially focused, since these models possess definitely slow magnetic relaxation and are conducive to ascertaining the synergistic effect between uniaxial magnetic anisotropy and steric configuration in enhancing effective barrier [7]. Moreover, the relatively simple geometric structures of such Dy(III) SMMs is conducive to probing into the magneto-structure correlation which is not clear for most lanthanide-based SIMs [8].