XAS and XMCD Investigation of Mn<sub>12</sub> Monolayers on Gold

Mannini, Matteo; Sainctavit, Philippe; Sessoli, Roberta; Moulin, Christophe; Pineider, Francesco; Arrio, Marie‐Anne; Cornia, Andrea; Gatteschi, Dante

doi:10.1002/chem.200800693

Cited by 128 publications

(139 citation statements)

References 39 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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“…There is growing interest in x-ray magnetic circular dichroism (XMCD) to study SMMs because of its ability to detect element-resolved magnetic moments combined with submonolayer sensitivity. [9][10][11][12][13][14] XMCD has been used to observe magnetic hysteresis, i.e., nonequilibrium magnetization in SMMs. [11][12][13] Here, we demonstrate that in endohedral SMMs the x-ray exposure itself can lead to an acceleration of magnetization relaxation.…”

mentioning

confidence: 99%

X-ray induced demagnetization of single-molecule magnets

Dreiser

Westerström

Piamonteze

et al. 2014

Applied Physics Letters

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Low-temperature x-ray magnetic circular dichroism measurements on the endohedral singlemolecule magnet DySc2N@C80 at the Dy M4,5 edges reveal a shrinking of the opening of the observed hysteresis with increasing x-ray flux. Time-dependent measurements show that the exposure of the molecules to x-rays resonant with the Dy M5 edge accelerates the relaxation of magnetization more than off-resonant x-rays. The results cannot be explained by a homogeneous temperature rise due to x-ray absorption. Moreover, the observed large demagnetization cross sections indicate that the resonant absorption of one x-ray photon induces the demagnetization of many molecules.

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“…Therefore, information stored by manipulating the direction of the molecule's spin vector is quickly lost 5,6,7,8,9,10 . This leads to the important experimental goal of identifying conditions in which the rate of magnetic relaxation of the adsorbed molecule is relatively small.…”

Section: Introductionmentioning

confidence: 99%

Stochastic Boltzmann equation for magnetic relaxation in high-spin molecules

2016

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We introduce the stochastic Boltzmann equation (SBE) as an approach for exploring the spin dynamics of magnetic molecules coupled to a stochastic environment. The SBE is a time-evolution equation for the probability density of the spin density matrix of the system. This probability density is relevant to experiments which take measurements on single molecules, in which probabilities of observing particular spin states (rather than ensemble averages) are of interest. By analogy with standard treatments of the regular Boltzmann equation, we propose a relaxation-time approximation for the SBE, and show that solutions to the SBE under the relaxation-time approximation can be obtained by performing simple trajectory simulations for the case of a boson gas environment.Cases where the relaxation-time approximation are satisfied can therefore be investigated by careful choice of the parameters for the boson gas environment, even if the actual environment is quite different from a boson gas. The application of the SBE approach is demonstrated through an illustrative example.

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XAS and XMCD Investigation of Mn₁₂ Monolayers on Gold

Cited by 128 publications

References 39 publications

Spintronic magnetic anisotropy

Spintronic magnetic anisotropy

X-ray induced demagnetization of single-molecule magnets

Stochastic Boltzmann equation for magnetic relaxation in high-spin molecules

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XAS and XMCD Investigation of Mn12 Monolayers on Gold

Cited by 128 publications

References 39 publications

Spintronic magnetic anisotropy

Spintronic magnetic anisotropy

X-ray induced demagnetization of single-molecule magnets

Stochastic Boltzmann equation for magnetic relaxation in high-spin molecules

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Product

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XAS and XMCD Investigation of Mn₁₂ Monolayers on Gold