Re: Why particules of magnetite put togheter donīt attract metalic objects?

Materials that are said to be ferromagnetic, such as magnetite, get their 
magnetic properties from an ordering of atoms (or molecules).  Within a large 
piece of ferromagnetic material, the ordering of atoms (or molecules) gives 
rise to regions called domains within which all the atomic magnets are oriented 
similarly, resulting in a stronger magnetic effect.  Also, in a large piece of 
ferromagnetic material that exhibits magnetic properties, the many domains are 
similarly oriented.  When you combine particles of magnetite, each particle 
might still have all its domains similarly oriented, but those of neighboring 
particles would have domains oriented in other directions.  So, while the 
individual particles may still exhibit magnetic properties, the collection of 
particles with randomly oriented magnetic fields would not because the fields 
of one particle would be countered by the fields of its neighbors.

Most high-school and college physics textbooks should have a discussion of 
ferromagnetism.  In addition, while searching the web, I found the following 
sites you may be interested in visiting;

[about magnetite]
http://mineral.galleries.com/minerals/oxides/magnetit/magnetit.htm 

[about ferromagnetism]
http://www.treasure-troves.com/physics/Ferromagnetism.html

Thanks for your question.

sid