Permanent magnets are magnets with magnetic fields that do not dissipate under normal circumstances. They are made from hard ferromagnetic materials, which are resistant to becoming demagnetized. Permanent magnets can be used for decoration (refrigerator magnets), for magnetic separation, or in electric motors and magnetic recording and storage media such as hard drives and magnetic tape.
Permanent magnets are made from material that will inherit the properties of a strong magnetic field when exposed to it. Many materials can temporarily inherit the properties of nearby magnetic material, but these properties often fade quickly, returning the material to its nonmagnetic state. In a permanent magnet the magnetic field continues to be exerted once it has been inherited. Alnico and hard ferrite are two examples of material capable of becoming a permanent magnet.
As noted above, the inherited magnetic field will be a permanent characteristic of the affected material. This field is continuous and will not weaken under most circumstances. Occasionally, if the material is subjected to a change in environment, the magnetic field can be altered. Such changes may include temperature variances or intentional demagnetizing of the material.
Under most circumstances, a magnetized material will retain its magnetic field in a variety of environments. Alnico, for example, will retain its properties in temperatures up to 550 °C. This wide-ranging tolerance of temperatures creates versatile and capable magnets. Other materials, such as those combined to make flexible magnets, retain their magnetism only up to 100 °C and have a much more limited range of applications.
Coercivity (or the coercive field) is the property of a material to resist demagnetization due to the intensity of the material's magnetic field. Coercivity is measured by the extent to which a demagnetizing field must be applied to reduce the material's magnetism to zero. Permanent magnets are composed of materials with a high coercivity which retain their inherited magnetic fields under most conditions, unless intentionally demagnetized.
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