Author:Site Editor Publish Time: 2020-08-11 Origin:Site
Magnets that can maintain their magnetism for a long time are called permanent magnets. Such as natural magnets (magnetite) and artificial magnets (alnico). In addition to permanent magnets, there are electromagnets that require electricity to be magnetic. Permanent magnets are also called hard magnets, which are not easy to lose magnetism and are not easy to be magnetized. But it does not mean that it will never lose magnetism. When the permanent magnet is heated above the Curie temperature, or in an environment with high reverse magnetic field strength, its magnetism will also decrease or disappear. Some magnets are brittle and may break at high temperatures. The maximum operating temperature of alnico magnets exceeds 540 °C (1,000 °F), samarium cobalt magnets and ferrites are about 300 °C (570 °F), neodymium magnets and soft magnets are about 140 °C ( 280 °F), but the actual value will still vary depending on the crystal grain of the material.
The materials used as magnetic conductors and electromagnets are mostly soft magnets. The polarity of the permanent magnet does not change, while the polarity of the soft magnet changes with the polarity of the applied magnetic field. They can attract iron objects. We call this property magnetism.
Neodymium Permanent Magnet
A magnet is magnetized by an external magnetic field in a closed circuit environment until the technology is saturated and then the external magnetic field is cancelled. At this time, the magnetic induction intensity of the magnet is called remanence. The unit of remanence (Br) is Tesla (T) and Gauss (Gs) 1Gs=0.0001T, which represents the maximum magnetic flux value that the magnet can provide. It can be seen from the demagnetization curve that it corresponds to the situation when the air gap is zero, so the magnetic induction intensity of the magnet in the actual magnetic circuit is less than the remanence. NdFeB magnet is the highest practical permanent magnet material for Br found today.
The unit of magnetic induction coercive force (Hcb) is ampere/meter (A/m) and Oersted (Oe) or 1Oe≈79.6A/m; when the magnet after the technical saturation magnetization is magnetized in the reverse direction, the magnetic induction The value of the reverse magnetic field strength required for the strength to drop to zero is called the magnetic coercive force (Hcb). But at this time, the magnetization of the magnet is not zero, but the effect of the applied reverse magnetic field and the magnetization of the magnet cancel each other out. (The external magnetic induction intensity is zero.) At this time, if the external magnetic field is cancelled, the magnet still has certain magnetic properties. The coercivity of neodymium iron boron is generally more than 11000 Oe.
Permanent magnets are mainly divided into: alloy permanent magnet materials, including rare earth permanent magnet materials (NdFeB Nd2Fe14B), samarium cobalt (SmCo), aluminum nickel cobalt (AlNiCo), and ferrite permanent magnet materials (Ferrite).
According to the different production processes, it can be divided into: sintered ferrite, bonded ferrite, and injection molded ferrite. These three processes are divided into isotropic and anisotropic magnets according to the different orientation of the magnetic crystal.