Although the wondrous combination of strength and plasticity is the main reason for developing glassy metals, they also have some surprising magnetic properties. Many metals are ferromagnetic, i.e., able to be magnetized by orienting their molecules in the same direction when a magnetic field is produced by an electric current in a coil round the metal. Some alloys do this more readily than others, but none like to have their state of magnetization changed; they all put up some measure of resistance.
When the current in the coil is switched off, the metal remains magnetized to some extent. To get rid of this remaining magnetization, i.e., to disorient the molecules into random directions again, a "coercive force" must be applied by letting some current flow in the opposite direction. How much is needed depends on the coercivity of the ferromagnetic metal. Cobalt steel, for example, is very recalcitrant, i.e., has a high coercivity, and is therefore well suited for permanent magnets. On the other hand, transformer cores should be magnetically "soft," for the current round them changes direction 60 times a second; if they were made of cobalt steel, their molecules would quickly heat up and, among other things, waste a lot of energy. They are therefore made of metals with low coercivity, such as soft iron, which realigns its magnetization without much opposition when the current is reversed; its molecules are like good Soviet citizens who painlessly reverse their thinking every time the party line is changed.
The trouble with such loyal citizens is that if their beliefs can be so easily changed, they couldn't have been very firm in the first place. Similarly, soft iron can easily be magnetized and de-magnetized, but not to such a high degree as some cobalt alloys.
There may be few true believers whose convictions are fanatical, yet easily changed; but what does exist now is cobalt alloys that are highly ferromagnetic, yet have low coercivity. They exist as glassy metals that have been cooled rapidly enough to prevent recrystallization.
Exactly why this is so is not yet completely understood. Indeed, there are still many points of contention in the theory of glassy metals, though it has advanced by leaps and bounds in the last couple of years. But whatever the reason, development of glassy ferromagnetic metals (or "ferromagnetic glasses") means advances in electrical machinery, where they can save energy by reducing "iron losses" (heat generated by reorienting molecules, i.e., remagnetizing metal with non-zero coercivity), as well as in magnetic memory devices, which they will make more efficient.
[More on the preceding 3 items: "Glassy Metals" by R.M.J. Cotterill, Amer. Scientist, July-Aug. 1976]
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Vol. 4, No. 2
Newsletter: Access to Energy Newsletter Archive Volume: Volume 4 Issue/No.: Vol. 4, No. 2 Date: October 01, 1976 12:42 PM Title: Who pays?
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