Nanomagnetism: Fundamentals and Applications

• Éditeur: Elsevier
• Année: 2014
• ISBN:
  9780080983554
• Sujet: Naturwissenschaften
• Sous-sujet: Physik

Nanomagnetism: Fundamentals and Applications is a complete guide to the theory and practical applications of magnetism at the nanometer scale. It covers a wide range of potential applications including materials science, medicine, and the environment. A tutorial covers the special magnetic properties of nanoscale systems in various environments, from free clusters to nanostructured materials. Subsequent chapters focus on the current state of research in theory and experiment in specific areas, and also include applications of nanoscale systems to synthesizing high-performance materials and devices.

• The only book on nanomagnetism to cover such a wide area of applications
• Includes a tutorial section that covers all the fundamental theory
• Serves as a comprehensive guide for people entering the field

Chapter 1

Tutorial Section on Nanomagnetism

Chris Binns Department of Physics and Astronomy, University of Leicester, Leicester, United Kingdom

Abstract

This chapter presents an overview of the special features of magnetism at the nanometer scale. It begins with a discussion of the reasons for novel magnetic behaviour and goes on to describe changes in orbital and spin magnetic moments in sufficiently small particles. The thermal stability of nanoparticles and superparamagnetism is also explored along with the critical size for single-domain behaviour. The interaction of magnetic nanoparticles with various environments and with each other is considered with a discussion on how their behaviour is modified.

Keywords

Nanomagnetism

Magnetic domains

Single-domain particles

Blocking temperature

Orbital magnetic moment

Spin magnetic moment

1 Why is the Nanometer Scale Special in Magnetism?

Given that distance scales in Physics range from 10^{− 35} m (the Planck length) to 10²⁶ m (the observable Universe), it is interesting to reflect on why the nanoscale (10^{− 9} m) is so important in materials. There are two main reasons. One is that for pieces of matter smaller than ~ 100 nm their fundamental properties are different to those of the bulk material. The other is that those fundamental properties become dependent on the size of the piece. This is quite alien to our macroscopic view of the world in which we take it for granted that when we cut a piece of material in half its fundamental properties remain unchanged. At the nanometer scale, a number of factors come into play to modify this behaviour. The proportion of atoms that are on the surface atomic layer, whose electronic states are modified relative to interior layers, becomes significant. For example in a 10-nm particle, 10% of the atoms are on the surface layer and this proportion increases to 50% in a 2-nm particle. Also in a metallic particle, the energy separation of conduction electron quantum states becomes significant relative to other energy parameters such as thermal and Zeeman energies. These and other effects mean that as the size of a piece of matter is reduced to ~ 100 nm and below, its electronic, magnetic, optical and chemical properties all start to evolve with size. This evolution is smooth near the upper boundary of the nanoscale region but at small sizes significant changes in behaviour can occur with the removal or addition of a single atom.

The detailed quantum mechanical theory of orbital and spin magnetic moments in nanoparticles is presented in Chapter 2, and here, the focus is on understanding the fundamental changes in magnetism at the nanoscale compared with bulk materials. To begin this tutorial, let us examine how intrinsic magnetic properties change as we reduce the size of a piece of material from the bulk through to a single atom. Interestingly, it was this thought process that led Leucippus and his student Demokritos to originally propose the concept of the atom around 400–450 BC. They argued that if matter was truly a continuum, then it could be cut into ever-smaller pieces ad infinitum so that in principle it would be possible to cut it into pieces of nothing that could then not be reassembled. To avoid this paradox, they hypothesised that there must be a smallest uncuttable piece—the atomon. With modern techniques, it is possible to synthesise and study materials at any size scale down to the atom, and if we carry out the Demokritos thought experiment, it turns out that the properties of the material start to change long before we reach the size of an atom. With respect to magnetic properties, arguably the first true size affect in materials is when the dimension of a magnet becomes too smal...

Table des matières

• Cover image
• Title page
• Table of Contents
• Copyright
• Contributors
• Preface
• Chapter 1: Tutorial Section on Nanomagnetism
• Chapter 2: Spin and Orbital Magnetism in Free Nanoparticles: Size, Composition, and Temperature Effects
• Chapter 3: Novel Methods for the Synthesis of Magnetic Nanoparticles
• Chapter 4: Magnetic Interactions: A Tool to Modify the Magnetic Properties of Materials Based on Nanoparticles
• Chapter 5: Magnetic States and Properties of Patterned Ferromagnetic Nanostructures
• Chapter 6: Medical Applications of Magnetic Nanoparticles
• Chapter 7: Environmental Applications of Magnetic Nanoparticles
• Index