In contrast to diamagnetic and paramagnetic materials which show a weak response to the presence of an applied magnetic field ferromagnetic materials show a very strong response. In contrast to paramagnetic materials, ferromagnetic substances may be maximumly magnetized in small, or negligible, fields at normal temperatures. The relationship between Je and ra/rd is of importance in the explanation of the ferromagnetic properties of alloys of nonferromagnetic transition elements. The chapter describes that ferrites for soft magnetic applications have the composition and structures. The curves of magnetization vs. temperature of many ferrites are similar in shape to those of ferromagnetic materials. Neel and others have shown that a substance could have considerable magnetic ordering within its component sublattices and still show little magnetization or susceptibility because the spins are opposed and Je is negative. The barium ferrites are between two and three times more resistant to demagnetization than the Alnico types.