Abstract/Details

Magnetostatic interactions in highly ordered self-assembled arrays of epsilon-cobalt nanoparticles


2007 2007

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Abstract (summary)

Interparticle magnetostatic interactions are studied in magnetic nanoparticle assemblies. &epsis;-Co nanoparticles obtained by solution chemistry techniques were used for these studies. These particles are highly monodisperse and self-assemble to form macroscopic ordered structures. 2D arrays (monolayers) were prepared via a modified Langmuir film technique and 3D arrays ( crystals) by colloidal crystallization. The interaction between the particles in the arrays is purely magnetostatic due to the surfactant layer on the particle surface that keeps particle cores well-separated for exchange interaction to become significant. Evidence of interparticle magnetic correlations is observed and quantitative estimates on correlation lengths are obtained in 2D and 3D arrays using the Small Angle Neutron Scattering (SANS) and Electron Holography, respectively. Dipolar coupled domains are found to be much larger (∼17 μm) in 2D monolayers compared to 3D crystals (∼70 nm). The differences in domain sizes are explained by shape anisotropy due to dimensionality and anisotropy averaging effects due to random crystallographic orientation of particles in the array. Macroscopic zero-field cooled (ZFC) measurements performed on MPMS-SQUID magnetometer were used to estimate the net anisotropy in the two structures. A change in curvature is observed in Arrott plots similar to exchange-based ferromagnets. The dipolar Curie temperature thus measured is consistent with theoretical estimates and is much higher than the blocking temperature of the particles. The macroscopic magnetic properties of the highly ordered nanoparticle assemblies with purely dipolar coupling are consistent with a very soft nanocrystalline ferromagnet.

Indexing (details)


Subject
Condensed matter physics
Classification
0611: Condensed matter physics
Identifier / keyword
Pure sciences; Cobalt; Magnetic nanoparticles; Magnetostatic interactions; Nanoparticles; Neutron scattering; Self-assembled arrays
Title
Magnetostatic interactions in highly ordered self-assembled arrays of epsilon-cobalt nanoparticles
Author
Sachan, Madhur
Number of pages
159
Publication year
2007
Degree date
2007
School code
0041
Source
DAI-B 69/08, Dissertation Abstracts International
Place of publication
Ann Arbor
Country of publication
United States
ISBN
9780549773764
Advisor
Majetich, Sara A.
University/institution
Carnegie Mellon University
University location
United States -- Pennsylvania
Degree
Ph.D.
Source type
Dissertations & Theses
Language
English
Document type
Dissertation/Thesis
Dissertation/thesis number
3326629
ProQuest document ID
304882362
Copyright
Database copyright ProQuest LLC; ProQuest does not claim copyright in the individual underlying works.
Document URL
http://search.proquest.com/docview/304882362/abstract
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