Magnetic Chucks, Permanent, Electro-Magnetic, Control, Rectangle, Round Magnetic Chuck, Lifting Magnet, Ferrite, Neodymium, Rare Earth

Magnets

---

Magnets are materials that produce a magnetic field of their own. Extreme examples of magnets are (1) "hard", or "permanent" magnets (like refrigerator magnets), which remember how they have been magnetized, and (2) "soft", or "impermanent" magnets (like the material of the refrigerator door), which lose their memory of previous magnetizations. "Soft" magnets are often used in electromagnets to enhance (often by factors of hundreds or thousands) the magnetic field of a current-carrying wire that has been wrapped around the magnet; when the current increases, so does the field of the "soft" magnet, which is much larger than the field due to the current. Permanent magnets occur naturally in some rocks, particularly lodestone, but they are now more commonly manufactured.

Materials without a permanent magnetic moment can, in the presence of magnetic fields, be attracted (paramagnetic), or repelled (diamagnetic). Liquid oxygen is paramagnetic; graphite is diamagnetic. "Soft" magnets, which are strongly attracted to magnetic fields, can be thought of as strongly paramagnetic; superconductors, which are strongly repelled by magnetic fields, can be thought of as strongly diamagnetic.

Rare-earth magnets

---

Rare-earth magnets are strong, permanent magnets made from alloys of rare earth elements. Rare-earth magnets are substantially stronger than ferrite or alnico magnets.

Magnetic fields produced by rare-earth magnets can be in excess of 1.2 teslas. Ferrite or ceramic magnets typically exhibit 50 to 100 milliteslas. Common applications of rare-earth magnets include computer hard drives, audio speakers and bicycle dynamos. Rare-earth magnets are used in stop motion animation as tie-downs when the use of traditional screw and nut tie-downs is impractical. Rare-earth magnets are used for diamagnetic levitation experimentation, the study of magnetic field dynamics and superconductor levitation. LSM launch technology found on roller coaster and other thrill rides utilize rare-earth magnets.

Permanent magnets and dipoles

---

All magnets appear to have at least one north pole (reckoned positive) and at least one south pole (reckoned negative), and the net pole strength of every magnet is zero. Despite their apparent reality, as suggested by the image at the top of the page, where iron filings concentrate in regions of large magnetic field, poles are not physical objects on or in the magnet. They are, rather, a useful concept for describing magnets. Rather than poles being the fundamental unit, it is the magnetic dipole that is the fundamental unit. A magnetic dipole can be thought of as a combination of a positive and a negative pole that are microscopically close to one another and inseparable. This is not a bad description of the magnetic dipole of an electron in a magnetic material.
By aligning a large number of these dipoles (say a million), and placing them head-to-tail in a line, we find that there is a north pole at one end and a south pole at the other, but all the intermediate north and south poles cancel out one another. The net effect is a very long dipole that appears to have poles only at its ends. Theories have been developed involving the possibility of north and south magnetic monopoles, but no magnetic monopole has yet been found.