What is it?
So simple, so fascinating, so fundamental to our modern society! The Earth is a giant magnetic as we all know from the
action of a compass. The vast majority of electrical power generation is through the medium of magnetism. Electric motors found in almost everything rely upon magnetism. All wireless transmissions -
in fact all radiation - is a beautiful matrix of electric and magnetic fields as so well described by Maxwell. Magnetism is fundamental to so much, so what is it
exactly? Well it seems that a magnetic field is created by the movement through space of electric charge. Well how does that work with a material like the coating
of a magnetic disk? At the atomic level in ferromagnetic materials (iron, cobalt and nickel), it is possible for electrons of the atoms to circulate in a way that creates a
tiny magnet. The tiny magnets tend to align creating a larger and stronger magnet. Now in a magnetic coating like on a computer disk or a tape, the ferrite material is magnetised by the write head
which applies a magnetic field in a particular direction, aligning the magnetic domains in the material. The alignment remains after the write head has gone - remembering the magnetising event! For
a practical memory medium, the trick is for the material to have little islands of magnetism that point in one direction or the other without undue interference.
Additionally, the material should be as uniform as possible so there are no holes or weak magnetic islands.
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