permanent magnet
Quick Summary
A permanent magnet is a material that retains its magnetism after the magnetizing force is removed. This magnetism arises from the motion of electric charges, creating a magnetic field. Ferromagnetic materials, such as iron, nickel, and cobalt, are capable of being permanently magnetized.1234
The process of magnetization involves aligning tiny magnetic domains within these materials. When a magnetizing field is applied, these domains reorient. In permanent magnets, this alignment persists, allowing them to produce a magnetic field outside themselves. Materials like steel can be better permanent magnets than soft iron due to internal imperfections that hinder domain wall movement, increasing coercivity. Permanent magnet motors, for example, utilize materials like neodymium-boron-iron or samarium-cobalt for their rotors.345
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- cobalt processingMagnetic alloys
The best permanent magnets contain a substantial quantity of cobalt.
Read MoreThe best permanent magnets contain a substantial quantity of cobalt.
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magnetismRemanenceA good permanent magnet must have a large spontaneous magnetization in zero field (i.e., a high retentivity) and a high coercive force to prevent its being easily demagnetized by an external field. Both of these imply a “fat,” almost rectangular hysteresis loop, typical of a hard magnetic…
Read MoreA good permanent magnet must have a large spontaneous magnetization in zero field (i.e., a high retentivity) and a high coercive force to prevent its being easily demagnetized by an external field. Both of these imply a “fat,” almost rectangular hysteresis loop, typical of a hard magnetic…
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rare-earth elementPermanent magnetsThe most prominent rare-earth intermetallic compound is Nd2Fe14B, which is ferromagnetic and, with proper heat treatment, becomes the hardest magnetic material known. Hence, this intermetallic compound is used as a permanent magnet in many applications. Its main uses are in electric motors (e.g.,…
Read MoreThe most prominent rare-earth intermetallic compound is Nd2Fe14B, which is ferromagnetic and, with proper heat treatment, becomes the hardest magnetic material known. Hence, this intermetallic compound is used as a permanent magnet in many applications. Its main uses are in electric motors (e.g.,…
Read More- rare-earth element
…an electrical traction motor, with permanent magnets containing rare-earth elements. In addition, modern media and communication devices—cell phones, televisions, and computers—all employ rare earths as magnets for speakers and hard drives and phosphors for optical displays. The amounts of rare earths used are quite small (0.1–5 percent by weight, except…
Read More…an electrical traction motor, with permanent magnets containing rare-earth elements. In addition, modern media and communication devices—cell phones, televisions, and computers—all employ rare earths as magnets for speakers and hard drives and phosphors for optical displays. The amounts of rare earths used are quite small (0.1–5 percent by weight, except…
Read More - rare-earth elementAbundance, occurrence, and reserves
…as large SmCo5- and Nd2Fe14B-based permanent magnets. All of these materials hold 25–30 percent by weight light lanthanides—much more than even the best rare-earth-containing ore (see below). However, the majority of consumer electronic devices contain only small amounts of rare earths. For example, a hard drive’s spindle magnet contains only…
Read More…as large SmCo5- and Nd2Fe14B-based permanent magnets. All of these materials hold 25–30 percent by weight light lanthanides—much more than even the best rare-earth-containing ore (see below). However, the majority of consumer electronic devices contain only small amounts of rare earths. For example, a hard drive’s spindle magnet contains only…
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