Source : Free On-Line Dictionary of Computing

magneto-optical disk
     
         Plastic or glass disks coated with a
        compound (often TbFeCo) with special properties.  The disk is
        read by bouncing a low-intensity laser off the disk.
        Originally the laser was infrared, but frequencies up to blue
        may be possible; the shorter the wavelength the higher the
        possible density.  The polarisation of the reflected light
        depends on the polarity of the stored magnetic field.
     
        To write, a higher-intensity laser is used to heat the
        material up to its Curie point, allowing its magnetisation to
        be altered and "frozen" as it cools.
     
        {Storage FAQ
       
     (http://www.cis.ohio-state.edu/hypertext/faq/usenet/arch-storage/part1/faq.html)}.
     
        (1995-03-15)