A ferrite core is a former that has been shaped in a particular way for use as part of an electromagnetic device. Ferrite is a magnetic material comprising of iron oxides, nickel, zinc and other compounds like manganese. Ferrite cores are distinguished from other ferrite devices like magnets in that they are made from a softer material, referred to as soft ferrites as opposed to hard ferrites. Soft ferrites like those used in cores are ferrimagnetic not ferromagnetic in that the materials have a very different magnetic ordering.

Ferrite cores are used in devices like chokes, transformers, circulators, and antenna cores in RF applications; they are also used as transformers and filtering devices in power supply design. The material’s low coercivity allows changes in the magnetization of the material without very much power dissipation (called hysteresis losses). The material has a high electrical resistance to current flow that suppresses spurious electrical currents that can cause dissipation of power, and lower efficiency.

It is important to have the right material for the right application. Materials are special combinations of iron oxides and other compounds that are optimized to the right frequency range and characteristics required for the application. Ferrite cores are also shaped to optimize performance pertaining to the application. Low frequency broadcast band antennas have rod-like cores because the coil and ferrite physical combination concentrates radio waves. Toroidal cores are formed to be better for higher frequency applications like RF filtering. Beads are a special form of a ferrite core that can have wire wound on it, or passed through it and are used typically used to suppress noise on power supplies.

Ferrites have a curie temperature, also known as the curie point. This is a point where the intrinsic magnetic moments of the material change directions. Spontaneous magnetism, the characteristic used in typical Ferrite applications, collapses at the curie point. The material becomes paramagnetic and the resultant practical effect is the device that the ferrite core is inside loses it's isolating characteristics and can begin dissipating more heat. This can lead to destruction of the component or failure of a circuit to work as designed because the device no longer works as intended.

Circulators are passive three port components made of ferrite material. They operate on a special principle called Faraday rotation that causes currents to flow in one direction and not the other. Hence, they are ideally suited to isolate inputs from outputs and are used in RF designs to isolate transmitters and receivers in shared antenna designs.