Magnetic hysteresis

thumb|A magnet made of [[alnico, a ferromagnetic iron alloy, with its keeper]] thumb|Paramagnetism, ferromagnetism, and spin waves Ferromagnetism is a property of certain materials (such as iron) that results in a significant, observable magnetic permeability, and in many cases, a significant magnetic coercivity, allowing the material to form a permanent magnet. Ferromagnetic materials are noticeably attracted to a magnet, which is a consequence of their substantial magnetic permeability.

Remanence or remanent magnetization or residual magnetism is the magnetization left behind in a ferromagnetic material (such as iron) after an external magnetic field is removed. Colloquially, when a magnet is "magnetized", it has remanence. The remanence of magnetic materials provides the magnetic memory in magnetic storage devices, and is used as a source of information on the past Earth's magnetic field in paleomagnetism. The word remanence is derived from remanent, meaning "that which remains".

thumb|upright=1.5|A family of hysteresis loops for grain-oriented electrical steel, a soft magnetic material. BR denotes [[retentivity and HC is the coercivity. The wider the outside loop is, the higher the coercivity. Movement on the loops is counterclockwise.]]

Degaussing, or deperming, is the process of decreasing or eliminating a remnant magnetic field. It is named after the gauss, a unit of magnetism, which in turn was named after Carl Friedrich Gauss. Due to magnetic hysteresis, it is generally not possible to reduce a magnetic field completely to zero, so degaussing typically induces a very small "known" field referred to as bias. Degaussing was originally applied to reduce ships' magnetic signatures during World War II. Degaussing is also used to reduce magnetic fields in tape recorders and cathode-ray tube displays, and to destroy data held on

application of an external magnetic field to a ferromagnet

(in some magnetic materials) state reached when an increase in applied external magnetic field H cannot increase the magnetization of the material further, so the total magnetic flux density B more or less levels off

occurs in bilayers (or multilayers) of magnetic materials where the hard magnetization behavior of an antiferromagnetic thin film causes a shift in the soft magnetization curve of a ferromagnetic film