The ferrofluids or the magnetic liquids are biphasic mediums obtained by physicochemical procedure to confer properties to some liquids and which integrate into their structure ultra fine, ferro and ferromagnetic subclass magnetic particles stabilized with certain substances. The extremely reduced dimensions of the particles within 0.30 - 20 nm (in the region of 10 nm, in a typical way) give a special role to their movement of thermal agitation in maintaining stability