ceramic - coated powdered ferromagnetic materials for forming magnetic articles , and which maintain the mechanical and magnetic properties of the articles at high temperatures , such as during annealing to relieve stresses induced during the forming operation . the ceramic coatings are formed by one of several techniques to provide an encapsulating layer on each ferromagnetic particle . the particles are then compacted to form a solid magnetic article , which can be annealed without concern for degrading the ceramic coating .