The Quest for Nanoscale Magnets: The example of [Mn12] Single Molecule Magnets

Rogez, Guillaume; Donnio, Bertrand; Terazzi, Emmanuel; Gallani, Jean‐Louis; Kappler, J.P.; Bucher, J. P.; Drillon, Marc

doi:10.1002/adma.200803020

Cited by 87 publications

(54 citation statements)

References 114 publications

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“…The value (S-31) is promising in view of the values obtained for state-of-the-art single-molecule magnets used in transport experiments, e.g., |D| ≈ 0.056 meV for a Fe 4 molecule embedded in a three-terminal device geometry 35,55 or |D| ≈ 0.06 meV for a Mn 12 molecule grafted on an insulating BN monolayer on Rh and studied by means of scanning tunneling spectroscopy 53 . Such experiments are challenging since molecular magnets often lose their magnetic anisotropy when deposited on a metal surface as required for device applications 53,[96][97][98] . In our spintronic approach the anisotropy is generated (rather than lost) when a high spin system is incorporated into a spin-valve device structure.…”

Section: Electrode Spin-polarization Pmentioning

confidence: 99%

Spintronic magnetic anisotropy

2013

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An attractive feature of magnetic adatoms and molecules for nanoscale applications is their superparamagnetism, the preferred alignment of their spin along an easy axis preventing undesired spin reversal. The underlying magnetic anisotropy barrier -a quadrupolar energy splitting -is internally generated by spin-orbit interaction and can nowadays be probed by electronic transport. Here we predict that in a much broader class of quantum-dot systems with spin larger than one-half, superparamagnetism may arise without spin-orbit interaction: by attaching ferromagnets a spintronic exchange field of quadrupolar nature is generated locally. It can be observed in conductance measurements and surprisingly leads to enhanced spin filtering even in a state with zero average spin. Analogously to the spintronic dipolar exchange field, responsible for a local spin torque, the effect is susceptible to electric control and increases with tunnel coupling as well as with spin polarization.The growing interest in nanomagnets, e.g., magnetic adatoms 1 and single-molecule magnets 2 is fueled by prospects of their application in novel spintronic devices whose functionality derives from their unique magnetic features 3 . A key property of such systems is their strong magnetic anisotropy leading to magnetic bistability, required for building blocks for nanoscale memory cells 4,5 and non-trivial quantum dynamics, useful for quantum information processing 6,7 . In either case, operational stability of such devices hinges heavily on the height of the energy barrier opposing the spin reversal. Though recently progress in the control over the magnetic anisotropy by synthesis 8 , mechanical straining 9 , atomic manipulation 10 or electrical gating 11 has been made, achieving of a high spin-reversal barrier still remains a challenge. Incorporating a nanomagnet into an electronic circuit may significantly alter its magnetic properties [12][13][14] , but may also be advantageous. One possible, spintronic route for manipulation of nanomagnets entails ferromagnetic electrodes and uses the spin torque due to spin-polarized scattering 15 or Coulomb interaction 16 , magnetic analogs of the proximity effect in superconducting junctions. In this article, we present another route that combines spintronics with molecular magnetism: high-spin quantum dots can acquire a significant magnetic anisotropy that is purely of spintronic origin, instead of deriving from the spin-orbit interaction, as the tunneling to ferromagnets induces a local, quadrupolar exchange field. Besides providing an alternative approach to electrical manipulation and engineering of superparamagnetic nanomagnets, this new quantity is of key importance for the analysis of experiments that probe atoms or molecules using highly spin-polarized electrodes. DIPOLAR VS. QUADRUPOLAR EXCHANGE FIELDThe origin of superparamagnetism, usually dominating the magnetic behaviour of a nanomagnet, is a magnetic anisotropy energy barrier. For instance, an adatom with a spin-degenerate ground multiplet (q...

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Section: Electrode Spin-polarization Pmentioning

confidence: 99%

Spintronic magnetic anisotropy

2013

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“…Generally, the above value of the anisotropy energy (ΔE) agrees well with the U eff value obtained from ac susceptibility measurements. In the case of Mn 12 SMM, the barrier can be well described by a double-well scheme [46] (Fig. 1.11), where a negative axial zero-field splitting (D) stabilizes the largest spin states m s = −10 (spin-up) and m s = +10 (spin-down) lying lowest in energy, and thus, it needs to surmount the energy barrier to reorient the spin via the perpendicular m s = 0 state [1].…”

Section: Effective Barrier (U Eff )mentioning

confidence: 99%

A Basis for Lanthanide Single-Molecule Magnets

Tang

Zhang

2015

Lanthanide Single Molecule Magnets

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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.

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“…5,6 Logically, one of the goals in this research field was to look for molecules with a high spin-flipping barrier. Since the magnetic anisotropy barrier depends on the square of the total spin of the ground state, the presence of ferromagnetic couplings is of crucial importance to reaching a large S value.…”

Section: Introductionmentioning

confidence: 99%

Exchange coupling and magnetic anisotropy of exchanged-biased quantum tunnelling single-molecule magnet Ni3Mn2 complexes using theoretical methods based on Density Functional Theory

Gómez‐Coca

Ruiz

2012

Dalton Trans.

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The magnetic properties of a new family of single-molecule magnet Ni(3)Mn(2) complexes were studied using theoretical methods based on Density Functional Theory (DFT). The first part of this study is devoted to analysing the exchange coupling constants, focusing on the intramolecular as well as the intermolecular interactions. The calculated intramolecular J values were in excellent agreement with the experimental data, which show that all the couplings are ferromagnetic, leading to an S = 7 ground state. The intermolecular interactions were investigated because the two complexes studied do not show tunnelling at zero magnetic field. Usually, this exchange-biased quantum tunnelling is attributed to the presence of intermolecular interactions calculated with the help of theoretical methods. The results indicate the presence of weak intermolecular antiferromagnetic couplings that cannot explain the ferromagnetic value found experimentally for one of the systems. In the second part, the goal is to analyse magnetic anisotropy through the calculation of the zero-field splitting parameters (D and E), using DFT methods including the spin-orbit effect.

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The Quest for Nanoscale Magnets: The example of [Mn12] Single Molecule Magnets

Cited by 87 publications

References 114 publications

Spintronic magnetic anisotropy

Spintronic magnetic anisotropy

A Basis for Lanthanide Single-Molecule Magnets

Exchange coupling and magnetic anisotropy of exchanged-biased quantum tunnelling single-molecule magnet Ni3Mn2 complexes using theoretical methods based on Density Functional Theory

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