Structural, electrical and magnetic properties of rare earth doped spinel ferrites

The first natural magnetic material found to man in pre historic time was magnetite (Fe3O4), which is now known as ferrous ferrite. The story of ferrites begins with the search for ferromagnetic material of usual high resistivity to obtain reasonable low eddy current losses. When ferrimagnetic materials placed in alternating field, eddy current generates into them, which dissipates energy. These losses can be reduced by lamination of ferrimagnetic core to restrict eddy current. Since, eddy current losses are inversely proportional to the resistivity; they can be minimized by use of magnetic materials of high resistivity. Ferrites having resistivity of up to 107Ωm as compared to 10-7Ωm of iron, reduces the eddy current losses in them to a negligible value, even at microwave frequencies