These are non-metallic compounds consisting of ferric oxide and one or two bivalent metal oxides such as NiO, MnO. These have resistivity of the order of 10⁹O cm, which reduces eddy current losses at high frequency. These magnets made out of it have high coercive force and square hysteresis loop. Magnetic permeability for these may be as high as 10,000 to 30,000. These materials are fabricated into shapes, such as triodes, E, U, I, beads and self shielding pot cores.

APPLICATIONS: CORES MADE OF ITS find use in filter applications up to 1MHz, high frequency power transformer operating at 10 to 100 KHz, pulse transforms up to 100MHz, adjustable air gap inductors recording heads and transducers.