Physical Information About Neodymium

For short explanations of technical terms see our Dictionary Of Magnetism.

Neodymium magnets (NdFeB-magnets)

... are permanent magnets.

This means: Ferromagnetic metal pieces are magnetized by a strong external magnetic field during the production process and then remain permanently magnetized. If handled properly, they will not lose their magnetic power even after decades.

... mainly contain of neodymium, iron and boron.

Neodymium is a chemical element from the group of rare earth metals or rare earths. It belongs to the lanthanides. The name neodymium means “new twin” (Greek neos and didymos); this naming refers to its similarity to lanthanum. Pure neodymium has a silvery shine, tarnishes quickly in air and oxidizes yellowish. Neodymium powder can self-ignite in air. It must therefore be stored airtight - or, in the case of neodymium magnets, coated and therefore protected from contact with air. Because of iron and boron being the main components in addition to neodymium, the short name according to the periodic table is NdFeB - or more precisely: Nd2Fe14B. Iron and boron, along with nickel and cobalt, are among the strongest ferromagnetic substances, i.e. the substances that can best be permanently magnetized.

... are described in their ferromagnetic properties using a hysteresis curve.

This magnetization curve provides information about the strength of the magnetization (remanence [Br]) as well as the required external magnetic force that leads to demagnetization (coercive field strength). However, the flux density in the entire space, i.e. the strength of the magnetic flux that flows through its surface, cannot be calculated analytically without complex finite element software. For cuboids and axially magnetized cylinders, the flux density can be approximately estimated using a formula along the magnetization axis.

... can only be heated to a limited extent.

To put it simply, magnetization means that an external magnetic field causes the atomic magnetic moments inside the workpiece to all be aligned parallel in the north-south direction. Then the workpiece is magnetic. However, this common alignment is canceled again if the temperature is too high (when the critical temperature, the so-called Curie temperature is exceeded). Neodymium magnets in their standard version must therefore not be heated above approx. 80°C. Neodymium magnets that can be heated more strongly when they are produced using special manufacturing processes.

... have a clear north and south pole.

It is also said: have a clear preferred direction. The direction of magnetization determines where the poles are located. Standardly this is done axially through the height axis.

... are unmarked, poles have to be detected.

Easiest is to take a red-and-green-painted education magnet. The north pole of the education magnet is detected by the south pole of the magnet you want to determine.

... are produced by sintering.

This means: All components are ground into a fine powder. This powder is pressed within a magnetic field and then sintered, i.e. solidified under pressure and heat. The components are therefore not merged. The workpiece is then magnetized by a strong external magnetic field. - are always coated. NdFeB is not stable in air but oxidizes slowly. This means that without an intact coating the magnet will decompose. To prevent this, neodymium magnets are at least triple coated with nickel, copper and nickel. Each of these layers typically has a thickness of 4-7 micrometers. When Ni coating is mentioned in the item descriptions, it is always Ni/Cu/Ni. If the surface has another coating than nickel, this is applied in addition to the three-fold coating. A gold coating is called Ni/Cu/Ni/Au, a copper coating is called Ni/Cu/Ni/Cu, a chrome coating is called Ni/Cu/Ni/Cr, etc. If the production was not carried out absolutely cleanly, it can It can also happen that the magnet partially decomposes under an externally intact coating. This can become apparent after several months or a few years as the coating bulges. In order to minimize the risk of decomposition, processing is done carefully and double checked to ensure that the surface coating is not damaged, either by chipping or by contact with substances harmful to the coating.

... can be magnetized in different grades for different strengths.

How strongly magnetized a neodymium magnet is can be seen from the letter N followed by a two-digit number (N35 to N52). The number indicates the energy density, i.e. the magnetic energy stored in the magnet: (WxH) max in MegaGaußOerstedt. The higher the number, the stronger the degree of magnetization. For two magnets with identical dimensions, the one with N48 is stronger than the one with N40. However, the volume of a magnet is more important than its degree of magnetization; the first rule is: the larger the magnet, the stronger it is. If the number is followed by one or two letters for the degree of magnetization, it indicates that this magnet can be heated to a higher temperature than standard neodymium. Instead of being heatable up to 80°C, heat resistance up to almost 200°C can also be achieved; The letters M, H, SH, UH or EH that follow the number provide information about the heatability.

... must not be processed mechanically and certainly not welded or soldered.

As described, neodymium reacts with oxygen. Consequently, the coating must not be damaged. Anyone who cuts or drills neodymium magnets would then have to be able to renew the coating again. Mechanical frictional heat can also cause the magnet to overheat, which irreversibly affects the magnetic force. You should never solder or weld neodymium magnets, as flying sparks can even lead to self-ignition.

... are produced in China, more than 97 % of the worldwide production is.