remanence

Remanence, or remanent magnetization, is the residual magnetization that remains in a ferromagnetic or ferrimagnetic material after an external magnetic field is removed. It reflects a material’s ability to retain magnetic information. It is commonly denoted Mr and is measured in amperes per meter (A/m). The corresponding remanent flux density Br is related by Br ≈ μ0 Mr when H is zero.

Remanent magnetization can form through several processes: isothermal remanent magnetization (IRM), obtained by applying a strong field in one direction and removing it; thermoremanent magnetization (TRM), developed when a material cools through its Curie point in a field; and related forms such as anhysteretic remanent magnetization (ARM) and saturation remanent magnetization (SRM).

Material factors influence remanence: domain structure, magnetocrystalline anisotropy, grain size and porosity, and temperature. Remanence decreases with increasing temperature toward the Curie point and can be altered by mechanical stress or demagnetization.

Measurement often uses a hysteresis loop, with Br at zero field indicating the remanent flux density; from M_r one can compute Br = μ0 M_r for isotropic cases. Applications include permanent magnets, magnetic storage devices, and palaeomagnetism, where remanence records historical magnetic field directions and intensities in rocks and sediments. Remanence also underpins studies of planetary and geological magnetic histories.