Remanent

Remanent, in magnetism, refers to the residual magnetization or magnetic flux that remains in a magnetic material after the external magnetic field that produced it is removed. It is commonly described as remanence and is quantified as remanent flux density (Br) or, when expressed as magnetization, remanent magnetization (Mr). In a typical hysteresis loop, Br is the value of the magnetic flux density B when the applied field H returns to zero, indicating how strongly the material retains its magnetization.

Remanence arises from the alignment of magnetic domains within ferromagnetic materials. Under a magnetizing field, domains grow and align; when the field is removed, many domains remain oriented, producing a residual magnetic field. The material may require a larger opposing field to bring the net magnetization to zero; this required field is the coercive field (Hc). Materials with high Br and high coercivity are called hard magnets and are used as permanent magnets, while soft magnets have low Br and low coercivity and are preferred for applications requiring rapid magnetization changes.

In geology and paleomagnetism, remanent magnetization (remanence) is the magnetization stored in rocks after the external field disappears. Different mechanisms produce remanence, including thermoremanent magnetization (TRM) formed as rocks cool in Earth's field, chemical remanent magnetization (CRM), and depositional remanent magnetization (DRM). These signals underpin reconstructions of past geomagnetic fields and plate movements.

Measurement of remanence is performed with magnetometers such as vibrating-sample magnetometers or SQUID devices, often by tracing B–H curves or recording B with zero applied field. The concept is central to magnetism, material science, and geology.