Book contents
- Frontmatter
- Contents
- Preface
- 1 Microstructural Analysis
- 2 Symmetry
- 3 Miller–Bravais Indices for Hexagonal Crystals
- 4 Stereographic Projection
- 5 Crystal Defects
- 6 Phase Diagrams
- 7 Free Energy Basis for Phase Diagrams
- 8 Ordering of Solid Solutions
- 9 Diffusion
- 10 Freezing
- 11 Phase Transformations
- 12 Surfaces
- 13 Bonding
- 14 Sintering
- 15 Amorphous Materials
- 16 Liquid Crystals
- 17 Molecular Morphology
- 18 Magnetic Behavior of Materials
- 19 Porous and Novel Materials
- 20 Shape Memory and Superelasticity
- 21 Calculations
- Index
- References
18 - Magnetic Behavior of Materials
Published online by Cambridge University Press: 10 December 2009
- Frontmatter
- Contents
- Preface
- 1 Microstructural Analysis
- 2 Symmetry
- 3 Miller–Bravais Indices for Hexagonal Crystals
- 4 Stereographic Projection
- 5 Crystal Defects
- 6 Phase Diagrams
- 7 Free Energy Basis for Phase Diagrams
- 8 Ordering of Solid Solutions
- 9 Diffusion
- 10 Freezing
- 11 Phase Transformations
- 12 Surfaces
- 13 Bonding
- 14 Sintering
- 15 Amorphous Materials
- 16 Liquid Crystals
- 17 Molecular Morphology
- 18 Magnetic Behavior of Materials
- 19 Porous and Novel Materials
- 20 Shape Memory and Superelasticity
- 21 Calculations
- Index
- References
Summary
Until about 200 years ago, magnetism was a mysterious phenomenon. The discovery of the magnetic effect in lodestone (Fe3O4) led to the first use of magnetism in compasses. When we speak of “magnetic behavior,” we usually mean ferromagnetic behavior. All materials have some response to a magnetic field. Paramagnetic materials weakly repulse magnetic fields and diamagnetic materials weakly attract magnetic fields.
Ferromagnetism
In contrast, ferromagnetic materials very strongly attract magnetic fields. There are only a few ferromagnetic elements. The important ones are iron, nickel, and cobalt. A few rare earths are ferromagnetic at low temperatures. Atoms of other transition elements may be ferromagnetic in alloys or compounds where the distance between atoms is different than in the elemental state. These include the manganese alloys Cu2MnAl, Cu2MnSn, Ag5MnAl, and MnBi. Table 18.1 lists a number of ferromagnetic elements, their Curie temperatures (temperature above which they cease to be ferromagnetic), and their saturation magnetizations.
Ferromagnetism arises because of an unbalance of electron spins in the 3d shell of the transition elements (the 4f shell for rare earths). The unbalanced spin causes a magnetic moment. In metals with valences of 1 or 3 (e.g., Cu or Al), each atom has an unbalance of spins, but the unbalance is random so there is no net effect. With the transition elements, the 3d and 4s energy bands overlap (Figure 18.1).
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- Chapter
- Information
- Materials ScienceAn Intermediate Text, pp. 184 - 201Publisher: Cambridge University PressPrint publication year: 2006