Single-Molecule Magnets:  Preparation and Properties of Mixed-Carboxylate Complexes [Mn12O12(O2CR)8(O2CR‘)8(H2O)4]

Soler, Mónica; Artus, Pau; Folting, Kirsten; Huffman, John C.; Hendrickson, David N.; Christou, George

doi:10.1021/ic0104048

Cited by 124 publications

(72 citation statements)

References 29 publications

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“…The crossover can occur in a narrow temperature interval with the field at which the system crosses the anisotropy barrier shifting abruptly with temperature, or the crossover can occur in a broad interval of temperature with this field changing smoothly [15,22,23]. The first studies were published on Mn 12 -Ac [11,12,13] 4 ] was prepared by the carboxylate substitution procedure described elsewhere [25], and crystallizes in triclinic space group P1 [26].…”

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confidence: 99%

Resonant Tunneling in Truly Axial SymmetryMn12Single-Molecule Magnets: Sharp Crossover between Thermally Assisted and Pure Quantum Tunneling

2006

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Magnetization measurements of a truly axial symmetry Mn12-tBuAc molecular nanomagnet with a spin ground state of S = 10 show resonance tunneling. This compound has the same magnetic anisotropy as Mn12-Ac but the molecules are better isolated and the crystals have less disorder and a higher symmetry. Hysteresis loop measurements at several temperatures reveal a well-resolved step fine-structure which is due to level crossings of excited states. All step positions can be modeled by a simple spin Hamiltonian. The crossover between thermally assisted and pure quantum tunneling can be investigated with unprecedented detail.PACS numbers: 75.50. Xx, 75.60.Jk, 75.75.+a, 75.45.+j Mn 12 -Ac for short, was the first single-molecule magnet (SMM), exhibiting slow magnetization relaxation of its S = 10 spin ground state which is split by axial zero-field splitting [1]. It was also the first system to show thermally assisted tunneling of magnetization [2,3,4]. During the last several years, many more SMMs have been discovered and they are now among the most promising candidates for observing the limits between classical and quantum physics since they have a well defined structure, spin ground state and magnetic anisotropy [5,6,7,9].Nevertheless, Mn 12 -Ac is still the most widely studied SMM [10,11,12,13,14,15,16,17,18,19,20,21,22]. While a rough understanding of the quantum phenomena in Mn 12 -Ac was clear from the early studies, a detailed understanding has not yet emerged. For example, current theoretical models assume the presence of quadratic and quartic transverse crystal-field interactions in the spin Hamiltonian, where the former has been ascribed to solvent disorder [21]. However, these interactions, which contain only even powers of the raising and lowering operators, do not provide an explanation for the observation of odd tunneling steps in the hysteresis loops. It has been proposed that easy-axis tilting might give the missing odd transverse interactions [18]. Although such solvent disorder induced tilts exist, the tilt values are still unclear [24]. Hyperfine, dipolar, and Dzyaloshinsky-Moriya interactions were also proposed to be responsible for odd transverse terms [10,13].Other theoretical and experimental studies concern the crossover between thermally assisted and pure quantum tunneling [11,12,13,14,15,22,23]. The crossover can occur in a narrow temperature interval with the field at which the system crosses the anisotropy barrier shifting abruptly with temperature, or the crossover can occur in a broad interval of temperature with this field changing smoothly [15,22,23]. The first studies were published on Mn 12 -Ac [11,12,13] We show that this compound has the same magnetic anisotropy as Mn 12 Ac but the molecules are better isolated and the crystals contain less disorder and a higher symmetry. Hysteresis loop measurements at several temperatures reveal a fine structure of steps which is due to the dominating energy level crossings. All step positions can be modeled by a simple spin Hamiltonian. The cr...

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confidence: 99%

Resonant Tunneling in Truly Axial SymmetryMn12Single-Molecule Magnets: Sharp Crossover between Thermally Assisted and Pure Quantum Tunneling

2006

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“…12 Mn 12 molecules have been synthesized with various ligands, and prior studies have showed that magnetic properties and exchange interactions of a SMM are strongly R-dependent. [13][14][15][16][17][18][19] To understand the effect of physical environment on properties of SMMs, especially that of a supporting substrate, it is desirable to place Mn 12 on well-defined surfaces and investigate the electronic and magnetic properties of individual molecules and monolayers. Much effort has already been made to deposit Mn 12 on various substrates, such as the metal Au(111), 20,21 the semi-metal Bi(111), 22 and even the ferromagnetic substrate Ni(111).…”

Section: Introductionmentioning

confidence: 99%

Single-molecule magnetMn12on graphene

Fry

Cheng

2014

Phys. Rev. B

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We study energetics, electronic and magnetic structures, and magnetic anisotropy barriers of a monolayer of single-molecule magnets (SMM), [Mn 12 O 12 (COOR) 16 ](H 2 O) 4 (abbreviated as Mn 12 , with R=H, CH 3 , C 6 H 5 and CHCl 2 ), on a graphene surface using spin-polarized density-functional theory with generalized gradient corrections and the inclusion of van der Waals interactions. We find that Mn 12 molecules with ligands -H, -CH 3 , and -C 6 H 5 are physically adsorbed on graphene through weak van der Waals interactions, and a much stronger ionic interaction occurs using a -CHCl 2 ligand. The strength of bonding is closely related to the charge transfer between the molecule and the graphene sheet and can be manipulated by strain in the graphene; specifically, tension enhances n-doping of graphene and compression encourages p-doping. The magnetic anisotropy barrier is computed by including the spin-orbit interaction within density-functional theory. The barriers for the Mn 12 molecules with ligands -H, -CH 3 and -C 6 H 5 on graphene surfaces remain unchanged (within 1 K) from those of isolated molecules because of their weak interaction, and a much larger reduction (10 K) is observed when using the -CHCl 2 ligand on graphene due to a substantial structural deformation as a consequence of the much stronger interaction. Neither strain in graphene nor charge transfer affects the magnetic anisotropy barrier significantly. Finally, we discuss the effect of strong correlation in the high spin state of a Mn 12 SMM and the consequence in SMM-surface adsorption.

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“…Furthermore, the spacing between the QMT steps associated with the FR species (~0.4 T) is not all that dissimilar to those of the SR species (~0.45 T), suggesting that they possess similar uniaxial anisotropy constants D. [14][15][16] Subsequently, detailed synthetic work by Christou, Hendrickson and co-workers, involving ligand substitution and crystallization from a variety of solvents, resulted in the discovery of many different forms of Mn 12 possessing essentially the same neutral Mn 12 O 12 core. 11,12,[17][18][19][20][21][22][23][24][25][26][27] However, important differences have been inferred from X-ray and magnetic studies. Most notably, the various Mn 12 complexes can be grouped broadly into two categories, i.e.…”

Section: Introductionmentioning

confidence: 99%

Anisotropy barrier reduction in fast-relaxingMn12single-molecule magnets

2009

Self Cite

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A novel angle-swept high-frequency electron paramagnetic resonance (HFEPR) technique is described that facilitates efficient in-situ alignment of single-crystal samples containing lowsymmetry magnetic species such as single-molecule magnets (SMMs). This cavity-based technique involves recording HFEPR spectra at fixed frequency and field, while sweeping the applied field orientation. The method is applied to the study of a low-symmetry Jahn-Teller variant of the extensively studied spin S = 10 Mn 12 SMMs (e.g. Mn 12 -acetate). The lowsymmetry complex also exhibits SMM behavior, but with a significantly reduced effective

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Single-Molecule Magnets: Preparation and Properties of Mixed-Carboxylate Complexes [Mn₁₂O₁₂(O₂CR)₈(O₂CR‘)₈(H₂O)₄]

Cited by 124 publications

References 29 publications

Resonant Tunneling in Truly Axial SymmetryMn12Single-Molecule Magnets: Sharp Crossover between Thermally Assisted and Pure Quantum Tunneling

Resonant Tunneling in Truly Axial SymmetryMn12Single-Molecule Magnets: Sharp Crossover between Thermally Assisted and Pure Quantum Tunneling

Single-molecule magnetMn12on graphene

Anisotropy barrier reduction in fast-relaxingMn12single-molecule magnets

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