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Notes
1 1 Magnetic moment or magnetic dipole moment, denoted by the symbol μ, summarizes the characteristics of a simple loop of current, producing a magnetic field, by the equation μ = IA, where I is the circulating current and A is the area enclosed by the loop. A simple loop such as this produces a dipolar magnetic field similar to that produced by a bar magnet with north and south poles.
2 2 Magnetostatic energy is the energy of a permanent magnet interacting with a static magnetic field.
3 3 A Bohr magneton (1μB) is the magnetic moment of a single free electron produced by its intrinsic angular momentum (spin).
4 4 The high magnetization was first observed in Fe67Co33 alloys, but the magnetically soft variant Fe50Co50 that is used commercially was patented in 1929 by G. W. Elmer.
5 5 Bacterium that infects the lungs of cystic fibrosis sufferers and causes inflammation and breathing problems.
6 6 You should find that your estimate is much larger than the critical size (~100 nm) for a single‐domain particle given in the text. The reason is that the exchange energy in a domain boundary can be reduced by a large factor by spreading it over a number of atomic layers. That is, instead of having an abrupt 180ª reversal of the magnetization across a single atomic plane, the magnetization rotates a fraction of 180° across each plane. This brings the critical size down to ~100 nm.
2 Nanoparticles and the Environment
In the previous chapter, the special properties of matter at nanoscale dimensions were presented and how this novel behavior could be exploited in technologies as diverse as advanced engineering materials and health care. This chapter is about nanoparticles and the environment, which encompasses naturally occurring nanoparticles and environmental applications of nanotechnology. Sections 2.1–2.7 discuss naturally occurring nanoparticles, both in our immediate environment, that is, the Earth's crust, oceans and atmosphere and out into deep space, where nanoparticles with their unique properties have helped shape the observable Universe. Section 2.7 describes the use of nanoparticles in addressing environmental issues via two important examples, that is, removing toxins from groundwater and recycling plastics.
2.1 Nanoparticles in the Atmosphere
The particles in the Earth's atmosphere have an important influence on the climate, but also have a poorly understood effect on life and our health. Improving our understanding of the effect of airborne nanoparticles is becoming increasingly important in a world where nanotechnology is poised to become a major activity. Clearly, the amount of manufactured nanoparticles will increase, so it is wise to be aware of how they interact with life and with the environment. It is important to emphasize, however, that manufactured nanoparticles are normally bound up in some material and the number of “loose” particles produced by nanotechnology will not necessarily become significant compared to those produced by the natural processes described below. In this chapter, the discussion is extended to encompass nanoparticles that are generated by existing human activities not directly involving nanotechnology, such as power generation, transport, etc. Obviously, these are not naturally occurring in the normal sense