CERAMIC MAGNETS
Ceramic (ferrite) magnets are composed of strontium carbonate and iron oxide. They are charcoal gray in color and usually appear in the forms of discs, rings, blocks, cylinders, and sometimes arcs for motors.

Applications of Ceramic Magnets:
 
•Speaker magnets
•DC brushless motors
•Magnetic Resonance Imaging (MRI)
•Magnetos used on lawnmowers and outboard motors
•DC permanent magnet motors (used in cars)
•Separators (separate ferrous material from non-ferrous)
•Used in magnetic assemblies designed for lifting, holding, retrieving and separating
•Magnetic Door Catcher
•Instrument and Meters
•Toys
•Arts and crafts

Attributes of Ceramic Magnets:

•Least expensive material compared to alnico and rare earth magnets
•High intrinsic coercive force
•Available in simple shapes only due to manufacturing process
•Lower service temperature than alnico, greater than rare earth  
•Lower energy product than alnico and rare earth magnets
•Most common grades of Y25,Y30,Y30H-1,Y30H-2,Y32,Y33 ceramic are 1, 5 and 8 (1-8 possible)

Tolerances:

For as pressed material, tolerance on the thickness (direction of magnetization) is ± .005inch. Other dimensions are ± 2% or ± .010inch, whichever is greater.

details:http://www.china-magnet.net/Ferrite.html