Remanence, also called remanent magnetization or residual magnetism, is the magnetic flux or strength of magnetism remaining in magnetic material or in an electronic circuit after an external magnetic field is withdrawn. Remanence in magnetic materials is a phenomenon utilized in magnetic storage devices, such as some computer memory and hard drives, while remanence in electronic circuits is typically an undesirable property of coils, transformers and generators.
The property of remanence is used to provide information in paleomagnetism, the study of how Earth's magnetism affects magnetic properties of sediment, rocks and archaeological items. By studying the magnetic properties of materials in these items, researchers acquire information about the ages of rocks or geologic layers and learn how tectonic plates moved during Earth's history.
Data remanence refers to the residual data remaining in magnetic storage devices used in electronic equipment such as hard drives, tape recorders and VCRs. Data remanence sometimes allows data to be retrieved from these devices even after they have been erased or wiped, posing a problem for entities that store sensitive data on magnetic media.
Sometimes people see the effects of remanence on their computer monitors or TVs when the buildup of remanence manifests as unwanted lines or color disturbances, often near the edges of the screens. Many TVs and monitors feature buttons or menu options to "degauss" the screen, a process that reduces remanence and derives its name from Gauss, a unit of magnetic field strength.