Remanence , remanent magnetization, Retentivity or residual magnetism is the magnetization left behind in a ferromagnetic material (such as iron) after an external magnetic field is removed. After certain classes of magnet material are “magnetized” they have remanence. The remanence of magnetic materials provides the magnetic memory in magnetic storage devices, and in common magnets or easily magnetized materials. In cases where where Remanence is unwanted, it can be removed by applying a negative inducing field in a proocess often called degaussing.
In magnetic studies and applications, ARkivak measures and reports residual magnetization using a VSM Magnetometer. The magnitude or strength of the material remanence is used to characterize permanent magnets; Neodymium magnets, for example, have a remanence approximately equal to 1.3 teslas
The default definition of magnetic remanence is the magnetization remaining in zero field after a large magnetic field is applied (enough to achieve saturation).
Source: Wikipedia