ferrite

Ferrite is a term used in materials science to refer to two related but distinct families of iron-based materials. In metallurgy, ferrite (specifically alpha-iron) is a body-centered cubic form of iron that exists at room temperature with very low carbon content and forms the magnetic matrix of many steels and cast irons. In magnetics and electronics, ferrites are ceramic ferrimagnetic compounds with the general formula MFe2O4, known as spinels, that are used as soft or hard magnetic materials.

Spinel ferrites consist of divalent metal ions (M2+) occupying tetrahedral and octahedral sites with Fe3+ ions. Common substitutions include Zn2+, Ni2+, Mn2+, Cu2+, and Co2+. They exhibit high electrical resistivity and tunable magnetic properties, enabling use in high-frequency magnetic components. Soft ferrites, such as MnZn and NiZn spinels, have low coercivity and high permeability, making them suitable for power transformers, inductors, and EMI suppression cores. Hard ferrites, such as BaFe12O19 and SrFe12O19 (hexagonal ferrites), have higher coercivity and are used as permanent magnets and in magnetic recording media.

Fabrication of ferrite ceramics typically involves solid-state synthesis from oxide precursors followed by calcination, milling, pressing, and sintering at temperatures around 1100–1500°C. The resulting materials are ceramic and brittle but exhibit stable magnetic properties and, for many compositions, high resistivity, reducing eddy-current losses at high frequencies. In consumer electronics, ferrite beads and cores are widely used to suppress high-frequency noise in cables and power lines.

See also: ferrimagnetism, spinel, magnetite, hexagonal ferrites.