Physical Properties of Nanometer-Scale Magnets

Awschalom, D. D.

doi:10.1007/978-1-4612-0531-9_12

Cited by 7 publications

(7 citation statements)

References 38 publications

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“…This is estimated by taking into account the coupling dipolar interaction constant, defined as the ratio of the dipolar to the anisotropy energies. Since the saturation magnetization markedly increases by annealing, we would expect, from the coupling constant R d ) (πM s 2 /12K a )(D/d) 3 (deduced from Stoner-Wolfarth particles where D and d are the average diameter and the interparticle distance, M s in emu/cm 3 (i.e. emu/g × density), respectively, to observe a change in the magnetization loop.…”

Section: Effect Of Annealing On the Nanoparticle Structurementioning

confidence: 99%

“…1,2 However, thermal fluctuations in magnetization and dipolar magnetic interactions among nanocrystals in an array are important limitations for their use as a support for magnetic storage at room temperature. 3 Actually, there is no clear solution to prevent the superparamagnetism phase transformation of nanocrystals of sizes below 10 nm. For any synthesis route, further postsynthesis treatment is needed to obtain ferromagnetic nanoparticles stable at room temperature.…”

Section: Introductionmentioning

confidence: 99%

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Seven-Nanometer Hexagonal Close Packed Cobalt Nanocrystals for High-Temperature Magnetic Applications through a Novel Annealing Process

2005

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Seven-nanometer cobalt nanocrystals are synthesized by colloidal chemistry. Gentle annealing induces a direct structural transition from a low crystalline state to the hexagonal close packed (hcp) phase without changing the size, size distribution, and the lauric acid passivating layer. The hcp structured nanocrystals can be easily redispersed in solvent for further application and processing. We found that the magnetization at saturation and the magnetic anisotropy are strongly modified through the annealing process. Monolayer self-assembly of the hcp cobalt nanocrystals is obtained, and due to the dipolar interaction, ferromagnetic behavior close to room temperature has been observed. This work demonstrates a novel approach for obtaining small size hcp structured cobalt magnetic nanocrystals for many technological applications.

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Section: Effect Of Annealing On the Nanoparticle Structurementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Seven-Nanometer Hexagonal Close Packed Cobalt Nanocrystals for High-Temperature Magnetic Applications through a Novel Annealing Process

2005

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“…Also, magnetic nanostructures often exhibit interesting properties, such as when the sample size becomes comparable to that of the spin-flip diffusion length and magnetic-domain-wall width. [7] The production of small dots of controlled size usually requires very sophisticated techniques. A highly efficient technique for the deposition of monodisperse and size-controlled clusters on surfaces uses size-selected molecular beams.…”

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confidence: 99%

Multilamellar‐Vesicle‐Assisted Electrodeposition of Inorganic Nanodots

et al. 2006

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Dots with dimensions below 100 nm are important in materials science for their original properties (luminescence, magnetism, catalysis, etc.), [1] and have been used to achieve higher data-storage densities, increased signal intensities, and higher reactivities, finding use in the computer industry, biotechnology, and catalysis. Although several techniques such as electron-and ion-beam lithography and scanning-probe methods are available today for producing nanostructures with size-dependent properties, [2][3][4] these are so expensive and time consuming that they hardly fulfill industrial requirements. Other techniques such as those based on masked surfaces [5,6] are less costly but are multistep approaches and usually limited to metallic deposition. We report a new process that combines a low-cost implementation and only a single step to produce nanodots over large areas with controlled size and density. This process is based on multilamellar vesicles, which serve as nanovectors. They incorporate metal ions such as copper ions, and under an appropriate electric field they can be directed towards an electrode. The reduction of ions on the electrode causes metal-nanodot production. Their density is controlled by the vesicle density and their size by the electric-field parameters.The manufacture of dots with sizes below 100 nm is motivated firstly by the specific properties exhibited by such nanostructures. These properties are due to surface effects and size reduction.[1] As an example, quantum dots are crystalline particles of semiconductor materials having unique optical properties. Since these are smaller in size than the wavelength of visible light, they cannot be seen under normal conditions, but become luminescent under UV light. The size of the particle controls the color of the emitted light. Also, magnetic nanostructures often exhibit interesting properties, such as when the sample size becomes comparable to that of the spin-flip diffusion length and magnetic-domain-wall width.[7]The production of small dots of controlled size usually requires very sophisticated techniques. A highly efficient technique for the deposition of monodisperse and size-controlled clusters on surfaces uses size-selected molecular beams.[8] Dots with a controlled number of atoms are then produced by laser evaporation or a sputter source. Electron-beam [2] or ion-beam lithography, [3] or nanolithography with scanning probe microscopes [4,9] such as dip-pen lithography, [10] are other examples of available techniques for deposition of dots with controlled size. However, these bottom-up techniques are so costly due to intricate fabrication processes and expensive equipment, and so time-consuming because of their step-by-step processes, that they are unsuitable as mass-production techniques.In some applications, like biosensor, biomaterial, or catalytic applications, the number of dots and the surface coverage are also of importance. Tailoring both features is essential to obtain functional structures inducing measurable signals [11]...

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“…However, with decreasing particle size, we come into conflict with the superparamagnetism caused by the reduction of the anisotropy energy per particle [35][36][37][38][39]. To overcome this problem, the use of hard magnetic nanomaterials is required.…”

Section: Control Of the Co Crystallinitymentioning

confidence: 99%

From the Co Nanocrystals to Their Self-Organizations: Towards Ferromagnetism at Room Temperature

Lisiecki

2012

Acta Phys. Pol. A

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Here, we show that rather uniform 7 nm Co nanocrystals self-organize into long-range two-and three--dimensional superlattices. Due to this ability we have to control the mesoscopic ordering; unexpected intrinsic collective chemical and physical properties have been discovered. By annealing treatment, a crystallographic transition from a polycrystalline fcc-to single crystalline hcp-Co phase is obtained leading to a drastic change in the magnetic properties such as an increase in the blocking temperature that can reach a value close to room temperature. Neither coalescence between nanocrystals nor oxidation of the Co material is observed. In these artificial solids, when the individual nanocrystal anisotropy is low, super-spin glass behavior is observed.

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Physical Properties of Nanometer-Scale Magnets

Cited by 7 publications

References 38 publications

Seven-Nanometer Hexagonal Close Packed Cobalt Nanocrystals for High-Temperature Magnetic Applications through a Novel Annealing Process

Seven-Nanometer Hexagonal Close Packed Cobalt Nanocrystals for High-Temperature Magnetic Applications through a Novel Annealing Process

Multilamellar‐Vesicle‐Assisted Electrodeposition of Inorganic Nanodots

From the Co Nanocrystals to Their Self-Organizations: Towards Ferromagnetism at Room Temperature

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