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Fundamentals and Applications of Magnetic Materials$
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Kannan M. Krishnan

Print publication date: 2016

Print ISBN-13: 9780199570447

Published to Oxford Scholarship Online: December 2016

DOI: 10.1093/acprof:oso/9780199570447.001.0001

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Fine Particles and Nanostructured Materials

Fine Particles and Nanostructured Materials

Chapter:
(p.358) 9 Fine Particles and Nanostructured Materials
Source:
Fundamentals and Applications of Magnetic Materials
Author(s):

Kannan M. Krishnan

Publisher:
Oxford University Press
DOI:10.1093/acprof:oso/9780199570447.003.0009

In this chapter, we discuss fundamental aspects of the magnetic behavior of fine particles and nanostructured materials, with emphasis on magnetic reversal, surface, finite size, and interaction effects. Energy barrier distributions and thermal excitations as a function of temperature and measurement time gives rise to superparamagnetism in fine particles below a characteristic size, or above a characteristic blocking temperature. The concept of magnetic viscosity, which maps the energy barrier distribution as well as the behavior of ferrofluids, including their field-dependent viscosity or magnetoviscosity is introduced. Time dependence of magnetization and their dynamics or response to an applied ac field, including the in-phase and loss components are described. Related experimental methods that are specific to determining their magnetic characteristics and the theoretical models used to interpret them are presented. These include Chantrell fitting of magnetization measurements to obtain nanoparticle size distributions, field-cooled and zero-field-cooled measurements, various remanence measurements to determine interactions, and Mössbauer spectroscopy. Some of the basic principles presented here will be further developed in later chapters that deal with specific applications in hard and soft magnets (§11), medicine and biology (§12), and information storage (§14).

Keywords:   magnetization reversals, superparamagnetism, blocking temperature, ZFC & FC measurements, magnetization dynamics, finite size and surface effects, ferrofluids, Mössbauer spectroscopy

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