Calculations of the susceptibility of interacting superparamagnetic particles

Chantrell, R.W.; Walmsley, N.S.; Gore, J.G.; Maylin, M.G.

doi:10.1103/physrevb.63.024410

Cited by 241 publications

(238 citation statements)

References 30 publications

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“…One indication that such interactions are indeed absent comes from the agreement between experimental and calculated data for χ(T ) in the superparamagnetic regime, where we observe the predicted slightly steeper than 1/T decrease, while calculations show that interactions would considerably flatten this decrease [47]. On the other hand, the absence of interactions can also be rationalized by comparing the island switching field H sw , the applied field H , and the stray field H dipol , created by all other islands at the location of one island.…”

Section: Quantifying the Contribution Of Perimeter Vs Surface Atoms mentioning

confidence: 84%

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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Section: Quantifying the Contribution Of Perimeter Vs Surface Atoms mentioning

confidence: 84%

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

Gambardella

Rusponi

Cren

et al. 2005

Comptes Rendus. Physique

View full text Add to dashboard Cite

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“…Interactions dominate the properties for small applied fields since it is expected that the applied field would dominate over the nearest-neighbor interactions as the system approaches saturation. 47 On the other hand, such dipolar interactions impinge on the ZFC magnetothermal curves as follows: at the beginning, when the sample is being cooled down, the magnetic moments of the particles present a disordered state and are randomly oriented. As the temperature increases, the particle moments tend to orientate along the direction of the field, which increases the magnetization following a particle distribution of energy barriers.…”

Section: Discussionmentioning

confidence: 99%

“…47 On the other hand, the existence of spin-glasslike phase in particle systems, observing an ϳH 2/3 dependence, has been pointed as a result of diverging relaxation times, attributed to competing interactions between surface spins ͑thus, disorder showed by a spin-glass phase shell surrounding a defined magnetic core͒. 4,12 In this case, if the spin-glasslike state would be due only to the existence of a frozen state of spins at the surface, this behavior would be observed as well in the ASD-25 sample, which presents an interface forming Fe-N bonds.…”

Section: Discussionmentioning

confidence: 99%

Effects of interparticle interactions in magneticFe/Si3N4granular systems

et al. 2010

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An experimental evidence of the progressive modification in the magnetic behavior of granular Fe/ Si 3 N 4 samples due to interaction effects between particles is reported. Microstructural features and local structure were determined by x-ray absorption spectroscopy and transmission electron microscopy to select granular samples with predetermined cluster size. Fe/ Si 3 N 4 systems have been characterized by ac-and dcmagnetization measurements to study the gradual evolution of magnetic properties of granular systems, where three different behaviors have been observed. As-deposited samples with Fe thickness layers of 2.5 nm, present a modified superparamagnetic behavior, due to very weak interactions between very small Fe clusters separated by a nonmagnetic FeN phase. An evolution of the average blocking temperature at intermediate fields ͑T B ϳ H 3/2 ͒ is observed, similar to noninteracting systems, but first signatures of a frozen spin state at low temperatures appear. Annealed samples exhibit a noticeable modification from the multilayer character to a random three-dimensional organization of Fe clusters embedded in a Si 3 N 4 matrix. After annealing, samples with initial Fe layer thickness of 0.7 nm provide iron cluster in the range of 1.3 nm and exhibit a superspinglass state, with a de Almeida-Thouless evolution of the energy barriers ͑T B ϳ H 2/3 ͒ that is explained in terms of increasing interparticle interactions. Moreover, annealed samples, with initial layer thickness of 1.3 nm, supply iron cluster of near 3 nm that present stronger interactions and yield a superferromagnetic state, likely provided by residual ultrasmall particles between the blocked clusters.

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“…At T Ͼ 65 K, the decrease in the magnetization when increasing temperature is much smoother than the observed for B-sample in both fields TRM curves. This behavior suggests that strong correlation between particles affects the remanence decay 21,22 in such a way that magnetization is maintained throughout a wide range of temperatures. In this case, magnetic interparticle interactions indicate that partial oxidation at room conditions does not provide a physical decoupling of the magnetic grains.…”

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confidence: 99%