remanens

Remanens, also called remanence or remanent magnetization, is the residual magnetization that remains in a ferromagnetic material after the external magnetic field has been removed. It reflects the portion of alignment of magnetic domains that persists due to magnetic anisotropy, lattice defects, and microstructure. The magnetic state after zero applied field is described by the remanent flux density Br and the corresponding remanent magnetization Mr. In a zero-field condition, Br equals μ0 times Mr, illustrating how a material can retain a magnetic signature without ongoing external influence.

The size and direction of remanens depend on material composition, manufacturing history, temperature, and prior magnetic exposure. Materials with strong magnetic anisotropy or high coercivity, such as permanent magnets, typically exhibit large remanent values, while soft magnetic materials often show smaller remanence though they can still retain noticeable magnetization after saturation. The relationship between remanence, saturation, and coercivity is visualized in the material’s hysteresis loop, where Br indicates remanence and Hc indicates the field needed to demagnetize the material.

Remanens has important applications in engineering and geology. In engineering, remanent magnetization is critical for the performance of permanent magnets, magnetic storage, transformers, and magnetic sensors. In geology, natural remanent magnetization (NRM) refers to the magnetization rocks acquire in Earth's past magnetic field, preserved over geological timescales and used in paleomagnetism to reconstruct past field directions and strengths.

Thermal and environmental factors influence remanens: it generally decreases with temperature and vanishes above the material’s critical temperature (Curie or Néel point). Demagnetization, thermal alteration, or mechanical shocks can modify or erase remanence.