Magnetic Anisotropy of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mn>3</mml:mn><mml:mi mathvariant="italic">d</mml:mi></mml:math>Transition-Metal Clusters

Pastor, G.; Dorantes-Dávila, J.; Pick, Štěpán; Dreyssé, H.

doi:10.1103/physrevlett.75.326

Cited by 161 publications

(97 citation statements)

References 13 publications

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“…The same theoretical interpretation can be applied to the atoms at the periphery of small metallic clusters. 4 In this case, the enhanced anisotropy at the surface extends to the inner atoms via the strong exchange interaction with them, which leads to an increase of the average anisotropy of even spherical clusters. 37 This interpretation has been confirmed by X-ray magnetic dichroism experiments performed on Au/Co/Au layers 35 and more recently also on Co disk-like aggregates supported on Au surfaces.…”

Section: Magnetic Anisotropymentioning

confidence: 99%

“…Their properties differ from those of the bulk magnets 1 because, as the size of the particles decreases, an increasing fraction of the total magnetic atoms lies at the surface. The electronic and magnetic structure of these atoms can be modified by the smaller number of neighbors as compared to the bulk [2][3][4] and/or by the interaction with the surrounding atoms of the matrix where the particles are dispersed. For example, it was shown by Van Leeuwen et al that the bonding of CO at the surface of Ni clusters induces quenching of the magnetic moments of those atoms located at the surface.…”

Section: Introductionmentioning

confidence: 99%

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Enhancement of the magnetic anisotropy of nanometer-sized Co clusters: Influence of the surface and of interparticle interactions

et al. 2002

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We study the magnetic properties of spherical Co clusters with diameters between 0.8 nm and 5.4 nm (25 to 7500 atoms) prepared by sequential sputtering of Co and Al2O3. The particle size distribution has been determined from the equilibrium susceptibility and magnetization data and it is compared to previous structural characterizations. The distribution of activation energies was independently obtained from a scaling plot of the ac susceptibility. Combining these two distributions we have accurately determined the effective anisotropy constant K ef f . We find that K ef f is enhanced with respect to the bulk value and that it is dominated by a strong anisotropy induced at the surface of the clusters. Interactions between the magnetic moments of adjacent layers are shown to increase the effective activation energy barrier for the reversal of the magnetic moments. Finally, this reversal is shown to proceed classically down to the lowest temperature investigated (1.8 K).

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Section: Magnetic Anisotropymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Enhancement of the magnetic anisotropy of nanometer-sized Co clusters: Influence of the surface and of interparticle interactions

et al. 2002

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“…It is well known that the magnetic properties of transition metal particles depend on the coordination of the constituent atoms [1][2][3][4]. Small clusters deposited on metal surfaces are predicted to have spin (m S ) and orbital (m L ) magnetic moments in between those of bulk compounds and free atoms [5][6][7], and to exhibit strong magnetic anisotropy with characteristic energies (E a ) of the order of 1-10 meV/atom, i.e., a factor 10 3 larger than bulk ferromagnetic metals [7,8].…”

Section: Introductionmentioning

confidence: 99%

Magnetic anisotropy from single atoms to large monodomain islands of Co/Pt(111)

Gambardella

Rusponi

Cren

et al. 2005

Comptes Rendus. Physique

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By studying the magnetic behavior of self-assembled Co islands on a single-crystal metal surface, Pt(111), we show how the magnetic anisotropy evolves from isolated atoms to monolayer islands and films. Single Co adatoms are found to have a giant magnetocrystalline anisotropy energy of E a = 9.3 ± 1.6 meV/atom arising from the combination of partly preserved orbital moments (m L = 1.1 µ B ) and strong spin-orbit coupling induced by the Pt substrate. Combined scanning tunneling microscopy and X-ray magnetic circular dichroism experiments performed for differently sized small two-dimensional Co islands establish a clear connection between E a and m L , both quantities decrease sharply with the lateral coordination of the magnetic atoms. In accordance with this, Kerr magnetometry experiments, again performed in conjunction with scanning tunneling microscopy, reveal that the anisotropy energy of large two-dimensional Co islands is almost entirely determined by the relatively low number of perimeter atoms, having E a = 0.9 ± 0.1 meV/atom. These results confirm theoretical predictions and are of fundamental value the understanding of how the magnetic anisotropy develops in finite-size magnetic particles. Identification of the role of perimeter and surface atoms opens up new opportunities for engineering the anisotropy and the moment of a magnetic nanostructure. RésuméAnisotropie magnétique de l'atome isolé aux îlots monocouches de Co/Pt(111). En étudiant les propriétés magnétiques de particules de Co auto assemblées sur une surface d'orientation (111) d'un monocristal de Pt, nous montrons comment l'anisotropie magnétique évolue de l'atome isolé aux îlots monocouches et aux films ultraminces. Nous trouvons que les atomes de Co isolés adsorbés en surface ont une énergie d'anisotropie magnétocrystalline de E a = 9.3 ± 1.6 meV/atome provenant de la combinaison d'un moment orbital conservé (m L = 1.1 µ B ) et d'un fort couplage spin-orbite induit par le substrat de Pt. Des expériences combinées de microscopie à effet tunnel et de dichroïsme circulaire magnétique à rayons X, effectués sur des îlots de Co de petit taille établissent une connexion claire entre E a et m L , chacune de ces quantités décroissant rapidement avec la coordination latérale des atomes magnétiques. En conformité avec ceci, nous trouvons en employant la magnétométrie par effet Kerr et le microscope à effet tunnel que l'énergie d'anisotropie de grands îlots bidimensionnels de Co est presque entiè-rement déterminée par le nombre relativement faible d'atomes au périmètre, ayant E a = 0.9 ± 0.1 meV/atome. Ces résultats confirment les prédictions théoriques et sont d'un intérêt fondamental pour comprendre comment l'anisotropie magnétique se développe dans les particules magnétiques de taille finie. L'identification du rôle des atomes au périmètre et des atomes de surface ouvre de nouvelles opportunités pour l'ingénierie de l'anisotropie et du moment de nanostructures magnétiques. Pour citer cet article : P. Gambardella et al., C. R. Physique 6 (200...

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“…Calculations for transition-metal clusters show that single spin flips can produce a significant change in the magnetic anisotropy energy [15], and measurements of Gd clusters indicate that anisotropy energies can vary significantly for clusters differing only by a single atom [16].…”

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confidence: 99%

Model for ferromagnetic nanograins with discrete electronic states

et al. 2001

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We propose a simple phenomenological model for an ultrasmall ferromagnetic grain, formulated in terms of the grain's discrete energy levels. We compare the model's predictions with recent measurements of the discrete tunneling spectrum through such a grain. The model can qualitatively account for the observed features if we assume (i) that the anisotropy energy varies among different eigenstates of one grain, and (ii) that nonequilibrium spin accumulation occurs.PACS numbers: 73.23. Hk, 75.50.Cc, 73.40.Gk What are the properties of individual quantum states in the electronic excitation spectrum of a nanometerscale ferromagnetic particle? This is becoming an increasingly important question, since the size of memory elements in magnetic storage technologies is decreasing extremely rapidly [1], and particles as small as 4 nm are coming under investigation [2]. In this size regime, the excitation spectrum becomes discrete; indeed, Guéron, Deshmukh, Myers and Ralph (GDMR) [3] have recently succeeded to resolve individual quantum states in the spectrum of ferromagnetic Cobalt nanograins, using single-electron tunneling spectroscopy. They found complex nonmonotonic and hysteretic energy level shifts in an applied magnetic field and an unexpected abundance of low-energy excitations, which could not be fully understood within the simple models used for ferromagnetic nanograins so far [3,4].In this Letter, we propose a phenomenological model for ferromagnetic nanograins that is explicitly formulated in terms of the discrete states occupied by the itinerant conduction electrons and capable of qualitatively explaining the observed features. The model is similar in spirit to that advanced independently by Canali and MacDonald [4], but our analysis includes two further ingredients beyond theirs: (i) mesoscopic fluctuations of the anisotropy energy (i.e. it may vary among different eigenstates), and (ii) nonequilibrium spin accumulation.Experimental Results.-GDMR studied Co-particles 1-4 nm in diameter. Assuming a hemispherical shape, the number of atoms in such grains is in the range N a ≈ 20-1500, and the total spin, s 0 ≈ 0.83N a [5], thus is s 0 ≈ 17 − 1250. In GDMR's devices, a grain is connected to two aluminum electrodes via aluminum oxide barriers. Its tunneling conductance consists of a series of distinct peaks (see Fig. 2 in [3]), whose positions yield a set of tunneling energies of the form [6] ∆E ± f i ≡ E N ±1 f − E N i each corresponding to the energy cost of some rate-limiting electron tunneling process |i N → |f N ±1 onto or off the grain. Here |i N denotes a discrete eigenstate, with eigenenergy E N i , of a grain with N electrons, etc. As the magnetic field is swept, the resonances for Cograins undergo energy shifts and crossings (Fig. 3 in [3], [7]). The resulting tunneling spectra have several properties that differ strikingly from those of previously-studied nonmagnetic Al and Au grains [8,9]: (P1): Many more low-energy excitations are observed than expected: For all values of magnetic field, the mean l...

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Magnetic Anisotropy of3dTransition-Metal Clusters

Cited by 161 publications

References 13 publications

Enhancement of the magnetic anisotropy of nanometer-sized Co clusters: Influence of the surface and of interparticle interactions

Enhancement of the magnetic anisotropy of nanometer-sized Co clusters: Influence of the surface and of interparticle interactions

Magnetic anisotropy from single atoms to large monodomain islands of Co/Pt(111)

Model for ferromagnetic nanograins with discrete electronic states

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