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15 May 2002

Volume 91, Issue 10, pp. 6227-8917

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Magnetization reversal in magnetostatically coupled dot arrays

H. Shima, K. Yu. Guslienko, V. Novosad, Y. Otani, K. Fukamichi, N. Kikuchi, O. Kitakami, and Y. Shimada

J. Appl. Phys. 91, 6952 (2002); http://dx.doi.org/10.1063/1.1450840 (3 pages) | Cited 6 times

Online Publication Date: 13 May 2002

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The submicron permalloy dots with variable diameter and interdot distance were microfabricated into a rectangular lattice by means of e-beam lithography and lift-off techniques. The hysteresis loops exhibit characteristic magnetization reversal accompanied by “nucleation” and “annihilation” of magnetic vortices inside the dots. The magnetic response of the samples with well-separated elements is isotropic in the plane. The arrays with a small interdot distance show magnetic anisotropy with the easy axis along the shortest period in the array. This anisotropy is originated from the interdot magnetostatic interaction. In the closely packed (when interdot distance is smaller than dot radius) arrays so that d/R<1, the magnetostatic interaction decreases the vortex nucleation and annihilation fields, and increases the initial susceptibility. © 2002 American Institute of Physics.
Show PACS
75.75.-c Magnetic properties of nanostructures
75.60.Jk Magnetization reversal mechanisms
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Bb Fe and its alloys
81.07.Ta Quantum dots
81.16.Nd Micro- and nanolithography
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Gw Magnetic anisotropy
75.30.Cr Saturation moments and magnetic susceptibilities

Magnetic domains and magnetostatic interactions of self-assembled Co dots

Chengtao Yu, J. Pearson, and Dongqi Li

J. Appl. Phys. 91, 6955 (2002); http://dx.doi.org/10.1063/1.1453334 (3 pages) | Cited 5 times

Online Publication Date: 13 May 2002

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Submicron quasihexagonal Co dots and dot chains have been grown epitaxially on Ru(0001) substrate with molecular beam epitaxy and investigated with magnetic force microscopy. All the dots exhibit in-plane single domains. The magnetization of the dots in a chain prefers to align along the chain direction due to inter-dot magnetostatic interactions. Micromagnetic calculations suggest that the observed single domains are metastable energetically and both vortex and single domain can exist in zero field. The inter-dot magnetostatic coupling, modeled with a dot pair, introduces a uniaxial anisotropy with easy axis along the pair/chain direction. The induced anisotropy field decreases with increasing inter-dot distance and approaches the dipolar limit. © 2002 American Institute of Physics.
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75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.60.Ch Domain walls and domain structure
75.30.Gw Magnetic anisotropy
75.30.Ds Spin waves

Production of monodispersed particles by using effective size selection

O. Perales-Perez, H. Sasaki, A. Kasuya, B. Jeyadevan, K. Tohji, T. Hihara, and K. Sumiyama

J. Appl. Phys. 91, 6958 (2002); http://dx.doi.org/10.1063/1.1452193 (3 pages) | Cited 10 times

Online Publication Date: 13 May 2002

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In this article we report the results of two size selection methods that are based on interfacial interaction between nanosize particles, magnetite in this case, anionic surfactants, and nonpolar solvents. It is proposed that by selecting a suitable surfactant type and/or conditions to modify the particle–particle separation distance, only smaller particles can be stabilized against aggregation and settling making a size sensitive separation possible. Using this phenomenon, an effective size selection at the nanosize level has been achieved and the preliminary results are presented here. Depending on the conditions, stable suspensions of nearly monodispersed nanoparticles of magnetite (diameter less than 10 nm and standard deviation, σ, below 0.2) were obtained from polydispersed powders (less than 40 nm in diameter and σ around 0.6) synthesized from aqueous solutions at 25 °C. Magnetization measurements of the fractions confirmed the effectiveness of the developed size selection methods. © 2002 American Institute of Physics.
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82.70.Kj Emulsions and suspensions
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Mm Magnetic liquids

Magnetic relaxation of iron nanoparticles

Ralph V. Chamberlin, Keith D. Humfeld, Dorothy Farrell, Saeki Yamamuro, Yumi Ijiri, and Sara A. Majetich

J. Appl. Phys. 91, 6961 (2002); http://dx.doi.org/10.1063/1.1452194 (3 pages) | Cited 10 times

Online Publication Date: 13 May 2002

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The magnetic relaxation of highly diluted monodisperse iron-based particles was measured between 10−5 and 104 s, for different temperatures and particle sizes. The decay over a very broad range of times indicated a distribution of energy barriers remained despite the narrow range of sizes. Many features of this decay could be explained using a percolation model of particles with weak dipolar interactions. However, this model did not predict the abrupt change in the decay rate at long times, which was observed for samples of both 8.0 and 5.5 nm particles below a threshold temperature. © 2002 American Institute of Physics.
Show PACS
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Bb Fe and its alloys
75.75.-c Magnetic properties of nanostructures
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
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