Introduction to Nanoscience and Nanotechnology. Chris Binns. Читать онлайн. Newlib. NEWLIB.NET

Автор: Chris Binns
Издательство: John Wiley & Sons Limited
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Жанр произведения: Отраслевые издания
Год издания: 0
isbn: 9781119172253
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as a method of high‐quality nanoparticle synthesis (see Chapter 5, Section 5.1.9).

      Interestingly, magnetic nanoparticles with a similar atomic structure have been found on a piece of meteorite known to have come from Mars [3] and this was taken as evidence that there was once life on Mars, though this analysis is controversial. Mars no longer has a significant planetary magnetic field, which disappeared some four billion years ago indicating that the nanofossils, if that is what they are, must be truly ancient. There are, however, localized magnetic fields around magnetic minerals on the surface that could have been used by magnetic bacteria more recently, though still in the distant past.

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      Source: Reproduced with the permission of the Int. J. Microbiol. from D. Schüler [2].

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      Returning to magnetism, a well‐known effect in sufficiently small particles is that, not only are they single domains but also the strength of their magnetism per atom is enhanced. The inset in Figure 1.7 shows the measured strength of magnetism (or the magnetic moment per atom) for Co nanoparticles as a function of size. The data are described in more detail below.

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      Source: Adapted from I. M. L. Billas et al. [4]; A. J. Cox et al. [5]; S. Apset et al. [6]; M. B. Knickelbein [7]; F. W. Paine et al. [8].

      In the Fe curve are also shown measurements (green circles) for Fe nanoparticles supported on a graphite surface and coated with Co [9] (see text).

      Throughout the whole size range in Figure 1.9, the fundamental magnetic behavior of the particles is size‐dependent. Do not lose sight of how strange a property this is and how it runs counter to our experience in the macroscopic world. It is as strange as a piece of metal changing color if we cut it in half. If Democritus was able to do his chopping experiment down to the nanoscale on Fe, when he reached a piece 100 nm across, which would be invisible in even the most powerful optical microscope, he would say that he had not yet reached the a‐tomon as up to then there would have been no observable change in properties. When he cut in half again, he would suddenly find his piece changing from magnetically dead to the full magnetic power of Fe with every atomic magnet aligned as the piece formed a single‐domain particle. He would exclaim “I have reached the a‐tomon,