Neodymium magnet

Last updated
A Nickel-plated neodymium magnet on a bracket from a hard disk drive Neodymag.jpg
A Nickel-plated neodymium magnet on a bracket from a hard disk drive
Nickel-plated neodymium magnet cubes Nd-magnet.jpg
Nickel-plated neodymium magnet cubes
Left: high-resolution transmission electron microscopy image of Nd2Fe14B; right: crystal structure with unit cell marked Neodymium Crystal Structure Nd2Fe14B.jpg
Left: high-resolution transmission electron microscopy image of Nd2Fe14B; right: crystal structure with unit cell marked
Inventor Masato Sagawa demonstrating a NdFeB magnet's force with 2 kg bottle. 1g-NdFeB-force = 2000g-water.png
Inventor Masato Sagawa demonstrating a NdFeB magnet's force with 2 kg bottle.

A neodymium magnet (also known as NdFeB, NIB or Neo magnet) is a permanent magnet made from an alloy of neodymium, iron, and boron to form the Nd2Fe14B tetragonal crystalline structure. [1] They are the most widely used type of rare-earth magnet. [2]

Contents

Developed independently in 1984 by General Motors and Sumitomo Special Metals, [3] [4] [5] neodymium magnets are the strongest type of permanent magnet available commercially. [1] [6] They have replaced other types of magnets in many applications in modern products that require strong permanent magnets, such as electric motors in cordless tools, hard disk drives and magnetic fasteners.

NdFeB magnets can be classified as sintered or bonded, depending on the manufacturing process used. [7] [8]

History

General Motors (GM) and Sumitomo Special Metals independently discovered the Nd2Fe14B compound almost simultaneously in 1984. [3] The research was initially driven by the high raw materials cost of samarium-cobalt permanent magnets (SmCo), which had been developed earlier. GM focused on the development of melt-spun nanocrystalline Nd2Fe14B magnets, while Sumitomo developed full-density sintered Nd2Fe14B magnets. [9]

GM commercialized its inventions of isotropic Neo powder, bonded neo magnets, and the related production processes by founding Magnequench in 1986 (Magnequench has since become part of Neo Materials Technology, Inc., which later merged into Molycorp). The company supplied melt-spun Nd2Fe14B powder to bonded magnet manufacturers. The Sumitomo facility became part of Hitachi, and has manufactured but also licensed other companies to produce sintered Nd2Fe14B magnets. Hitachi has held more than 600 patents covering neodymium magnets. [9]

Chinese manufacturers have become a dominant force in neodymium magnet production, based on their control of much of the world's rare-earth mines. [10]

The United States Department of Energy has identified a need to find substitutes for rare-earth metals in permanent magnet technology and has funded such research. The Advanced Research Projects Agency-Energy has sponsored a Rare Earth Alternatives in Critical Technologies (REACT) program, to develop alternative materials. In 2011, ARPA-E awarded 31.6 million dollars to fund Rare-Earth Substitute projects. [11] Because of its role in permanent magnets used for wind turbines, it has been argued that neodymium will be one of the main objects of geopolitical competition in a world running on renewable energy. This perspective has been criticized for failing to recognize that most wind turbines do not use permanent magnets and for underestimating the power of economic incentives for expanded production. [12]

Properties

Neodymium magnets (small cylinders) lifting steel spheres. Such magnets can lift thousands of times their own weight. Neodymium magnet lifting spheres.jpg
Neodymium magnets (small cylinders) lifting steel spheres. Such magnets can lift thousands of times their own weight.
Ferrofluid on a glass plate displays the strong magnetic field of the neodymium magnet underneath. Ferrofluid Magnet under glass.jpg
Ferrofluid on a glass plate displays the strong magnetic field of the neodymium magnet underneath.

Magnetic properties

In its pure form, neodymium has magnetic properties—specifically, it is antiferromagnetic, but only at low temperatures, below 19 K (−254.2 °C; −425.5 °F). However, some compounds of neodymium with transition metals such as iron are ferromagnetic, with Curie temperatures well above room temperature. These are used to make neodymium magnets.

The strength of neodymium magnets is the result of several factors. The most important is that the tetragonal Nd2Fe14B crystal structure has exceptionally high uniaxial magnetocrystalline anisotropy (HA ≈ 7  T – magnetic field strength H in units of A/m versus magnetic moment in A·m2). [13] [3] This means a crystal of the material preferentially magnetizes along a specific crystal axis but is very difficult to magnetize in other directions. Like other magnets, the neodymium magnet alloy is composed of microcrystalline grains which are aligned in a powerful magnetic field during manufacture so their magnetic axes all point in the same direction. The resistance of the crystal lattice to turning its direction of magnetization gives the compound a very high coercivity, or resistance to being demagnetized.

The neodymium atom can have a large magnetic dipole moment because it has 4 unpaired electrons in its electron structure [14] as opposed to (on average) 3 in iron. In a magnet it is the unpaired electrons, aligned so that their spin is in the same direction, which generate the magnetic field. This gives the Nd2Fe14B compound a high saturation magnetization (Js ≈ 1.6  T or 16  kG) and a remanent magnetization of typically 1.3 teslas. Therefore, as the maximum energy density is proportional to Js2, this magnetic phase has the potential for storing large amounts of magnetic energy (BHmax ≈ 512 kJ/m3 or 64  MG·Oe).

This magnetic energy value is about 18 times greater than "ordinary" ferrite magnets by volume and 12 times by mass. This magnetic energy property is higher in NdFeB alloys than in samarium cobalt (SmCo) magnets, which were the first type of rare-earth magnet to be commercialized. In practice, the magnetic properties of neodymium magnets depend on the alloy composition, microstructure, and manufacturing technique employed.

The Nd2Fe14B crystal structure can be described as alternating layers of iron atoms and a neodymium-boron compound. [3] The diamagnetic boron atoms do not contribute directly to the magnetism but improve cohesion by strong covalent bonding. [3] The relatively low rare earth content (12% by volume, 26.7% by mass) and the relative abundance of neodymium and iron compared with samarium and cobalt makes neodymium magnets lower in price than the other major rare-earth magnet family, samarium–cobalt magnets. [3]

Although they have higher remanence and much higher coercivity and energy product, neodymium magnets have lower Curie temperature than many other types of magnets. Special neodymium magnet alloys that include terbium and dysprosium have been developed that have higher Curie temperature, allowing them to tolerate higher temperatures. [15]

Magnetic properties of various permanent magnets
Magnet Br
(T)		 Hci
(kA/m)		BHmax
(kJ/m3)		 TC
(°C)(°F)
Nd2Fe14B, sintered1.0–1.4750–2000200–440310–400590–752
Nd2Fe14B, bonded0.6–0.7600–120060–100310–400590–752
SmCo5, sintered0.8–1.1600–2000120–2007201328
Sm(Co, Fe, Cu, Zr)7, sintered0.9–1.15450–1300150–2408001472
Alnico, sintered0.6–1.427510–88700–8601292–1580
Sr-ferrite, sintered0.2–0.78100–30010–40450842

Physical and mechanical properties

Photomicrograph of NdFeB. The jagged edged regions are the metal crystals, and the stripes within are the magnetic domains. NdFeB-Domains.jpg
Photomicrograph of NdFeB. The jagged edged regions are the metal crystals, and the stripes within are the magnetic domains.
Comparison of physical properties of sintered neodymium and Sm-Co magnets [16]
PropertyNeodymium Sm-Co
Remanence (T)1–1.50.8–1.16
Coercivity (MA/m)0.875–2.790.493–2.79
Recoil permeability 1.051.05–1.1
Temperature coefficient of remanence (%/K)−(0.12–0.09)−(0.05–0.03)
Temperature coefficient of coercivity (%/K)−(0.65–0.40)−(0.30–0.15)
Curie temperature (°C)310–370700–850
Density (g/cm3)7.3–7.78.2–8.5
Thermal expansion coefficient, parallel to magnetization (1/K)(3–4)×10−6(5–9)×10−6
Thermal expansion coefficient, perpendicular to magnetization (1/K)(1–3)×10−6(10–13)×10−6
Flexural strength (N/mm2)200–400150–180
Compressive strength (N/mm2)1000–1100800–1000
Tensile strength (N/mm2)80–9035–40
Vickers hardness (HV)500–650400–650
Electrical resistivity (Ω·cm)(110–170)×10−6(50–90)×10−6

Corrosion

These neodymium magnets corroded severely after five months of weather exposure. NdFeB corrosion.jpg
These neodymium magnets corroded severely after five months of weather exposure.

Sintered Nd2Fe14B tends to be vulnerable to corrosion, especially along grain boundaries of a sintered magnet. This type of corrosion can cause serious deterioration, including crumbling of a magnet into a powder of small magnetic particles, or spalling of a surface layer.

This vulnerability is addressed in many commercial products by adding a protective coating to prevent exposure to the atmosphere. Nickel, nickel-copper-nickel and zinc platings are the standard methods, although plating with other metals, or polymer and lacquer protective coatings, are also in use. [17]

Temperature sensitivity

Neodymium has a negative coefficient, meaning the coercivity along with the magnetic energy density (BHmax) decreases as temperature increases. Neodymium-iron-boron magnets have high coercivity at room temperature, but as the temperature rises above 100 °C (212 °F), the coercivity decreases drastically until the Curie temperature (around 320 °C or 608 °F). This fall in coercivity limits the efficiency of the magnet under high-temperature conditions, such as in wind turbines and hybrid vehicle motors. Dysprosium (Dy) or terbium (Tb) is added to curb the fall in performance from temperature changes. This addition makes the magnets more costly to produce. [18]

Grades

Neodymium magnets are graded according to their maximum energy product, which relates to the magnetic flux output per unit volume. Higher values indicate stronger magnets. For sintered NdFeB magnets, there is a widely recognized international classification. Their values range from N28 up to N55 with a theoretical maximum at N64. The first letter N before the values is short for neodymium, meaning sintered NdFeB magnets. Letters following the values indicate intrinsic coercivity and maximum operating temperatures (positively correlated with the Curie temperature), which range from default (up to 80 °C or 176 °F) to TH (230 °C or 446 °F). [19] [20] [21]

Grades of sintered NdFeB magnets: [7] [ further explanation needed ] [22] [ unreliable source? ] [23]

Production

There are two principal neodymium magnet manufacturing methods:

Bonded neo Nd-Fe-B powder is bound in a matrix of a thermoplastic polymer to form the magnets. The magnetic alloy material is formed by splat quenching onto a water-cooled drum. This metal ribbon is crushed to a powder and then heat-treated to improve its coercivity. The powder is mixed with a polymer to form a mouldable putty, similar to a glass-filled polymer. This is pelletised for storage and can later be shaped by injection moulding. An external magnetic field is applied during the moulding process, orienting the field of the completed magnet. [25] [26]

In 2015, Nitto Denko of Japan announced their development of a new method of sintering neodymium magnet material. The method exploits an "organic/inorganic hybrid technology" to form a clay-like mixture that can be fashioned into various shapes for sintering. It is said to be possible to control a non-uniform orientation of the magnetic field in the sintered material to locally concentrate the field, for instance to improve the performance of electric motors. Mass production is planned for 2017. [27] [28] [ needs update ]

As of 2012, 50,000  tons of neodymium magnets are produced officially each year in China, and 80,000 tons in a "company-by-company" build-up done in 2013. [29] China produces more than 95% of rare earth elements and produces about 76% of the world's total rare-earth magnets, as well as most of the world's neodymium. [30] [9]

Applications

Existing magnet applications

Ring magnets 2 Ferrite ring magnets.jpg
Ring magnets
Most hard disk drives incorporate strong magnets Hdd od srodka.jpg
Most hard disk drives incorporate strong magnets
This manually-powered flashlight uses a neodymium magnet to generate electricity Linear induction flashlight.jpg
This manually-powered flashlight uses a neodymium magnet to generate electricity

Neodymium magnets have replaced alnico and ferrite magnets in many of the myriad applications in modern technology where strong permanent magnets are required, because their greater strength allows the use of smaller, lighter magnets for a given application. Some examples are:

New applications

Neodymium magnet spheres assembled in the shape of a cube NeoCube.jpg
Neodymium magnet spheres assembled in the shape of a cube

The greater strength of neodymium magnets has inspired new applications in areas where magnets were not used before, such as magnetic jewelry clasps, keeping up foil insulation, children's magnetic building sets (and other neodymium magnet toys) and as part of the closing mechanism of modern sport parachute equipment. [33] They are the main metal in the formerly popular desk-toy magnets, "Buckyballs" and "Buckycubes", though some U.S. retailers have chosen not to sell them because of child-safety concerns, [34] and they have been banned in Canada for the same reason. [35] While a similar ban has been lifted in the United States in 2016, the minimum age requirement advised by the CPSC is now 14, and there are now new warning label requirements. [36]

The strength and magnetic field homogeneity on neodymium magnets has also opened new applications in the medical field with the introduction of open magnetic resonance imaging (MRI) scanners used to image the body in radiology departments as an alternative to superconducting magnets that use a coil of superconducting wire to produce the magnetic field. [37]

Neodymium magnets are used as a surgically placed anti-reflux system which is a band of magnets [38] surgically implanted around the lower esophageal sphincter to treat gastroesophageal reflux disease (GERD). [39] They have also been implanted in the fingertips in order to provide sensory perception of magnetic fields, [40] though this is an experimental procedure only popular among biohackers and grinders. [41]

Neodymium is used as a magnetic crane which is a lifting device that lifts objects by magnetic force. [42] These cranes lift ferrous materials like steel plates, pipes, and scrap metal using the persistent magnetic field of the permanent magnets without requiring a continuous power supply. [43] Magnetic cranes are used in scrap yards, shipyards, warehouses, and manufacturing plants. [44]

Hazards

The greater forces exerted by rare-earth magnets create hazards that may not occur with other types of magnet. Neodymium magnets larger than a few cubic centimeters are strong enough to cause injuries to body parts pinched between two magnets, or a magnet and a ferrous metal surface, even causing broken bones. [45]

Magnets that get too near each other can strike each other with enough force to chip and shatter the brittle magnets, and the flying chips can cause various injuries, especially eye injuries. There have even been cases where young children who have swallowed several magnets have had sections of the digestive tract pinched between two magnets, causing injury or death. [46] Also this could be a serious health risk if working with machines that have magnets in or attached to them. [47]

The stronger magnetic fields can be hazardous to mechanical and electronic devices, as they can erase magnetic media such as floppy disks and credit cards, and magnetize watches and the shadow masks of CRT-type monitors at a greater distance than other types of magnet. In some cases, chipped magnets can act as a fire hazard as they come together, sending sparks flying as if they were a lighter flint, because some neodymium magnets contain ferrocerium.

See also

Related Research Articles

<span class="mw-page-title-main">Dysprosium</span> Chemical element with atomic number 66 (Dy)

Dysprosium is a chemical element; it has symbol Dy and atomic number 66. It is a rare-earth element in the lanthanide series with a metallic silver luster. Dysprosium is never found in nature as a free element, though, like other lanthanides, it is found in various minerals, such as xenotime. Naturally occurring dysprosium is composed of seven isotopes, the most abundant of which is 164Dy.

<span class="mw-page-title-main">Ferromagnetism</span> Mechanism by which materials form into and are attracted to magnets

Ferromagnetism is a property of certain materials that results in a significant, observable magnetic permeability, and in many cases, a significant magnetic coercivity, allowing the material to form a permanent magnet. Ferromagnetic materials are noticeably attracted to a magnet, which is a consequence of their substantial magnetic permeability.

<span class="mw-page-title-main">Neodymium</span> Chemical element with atomic number 60 (Nd)

Neodymium is a chemical element; it has symbol Nd and atomic number 60. It is the fourth member of the lanthanide series and is considered to be one of the rare-earth metals. It is a hard, slightly malleable, silvery metal that quickly tarnishes in air and moisture. When oxidized, neodymium reacts quickly producing pink, purple/blue and yellow compounds in the +2, +3 and +4 oxidation states. It is generally regarded as having one of the most complex spectra of the elements. Neodymium was discovered in 1885 by the Austrian chemist Carl Auer von Welsbach, who also discovered praseodymium. It is present in significant quantities in the minerals monazite and bastnäsite. Neodymium is not found naturally in metallic form or unmixed with other lanthanides, and it is usually refined for general use. Neodymium is fairly common—about as common as cobalt, nickel, or copper—and is widely distributed in the Earth's crust. Most of the world's commercial neodymium is mined in China, as is the case with many other rare-earth metals.

<span class="mw-page-title-main">Paramagnetism</span> Weak, attractive magnetism possessed by most elements and some compounds

Paramagnetism is a form of magnetism whereby some materials are weakly attracted by an externally applied magnetic field, and form internal, induced magnetic fields in the direction of the applied magnetic field. In contrast with this behavior, diamagnetic materials are repelled by magnetic fields and form induced magnetic fields in the direction opposite to that of the applied magnetic field. Paramagnetic materials include most chemical elements and some compounds; they have a relative magnetic permeability slightly greater than 1 and hence are attracted to magnetic fields. The magnetic moment induced by the applied field is linear in the field strength and rather weak. It typically requires a sensitive analytical balance to detect the effect and modern measurements on paramagnetic materials are often conducted with a SQUID magnetometer.

<span class="mw-page-title-main">Samarium</span> Chemical element with atomic number 62 (Sm)

Samarium is a chemical element; it has symbol Sm and atomic number 62. It is a moderately hard silvery metal that slowly oxidizes in air. Being a typical member of the lanthanide series, samarium usually has the oxidation state +3. Compounds of samarium(II) are also known, most notably the monoxide SmO, monochalcogenides SmS, SmSe and SmTe, as well as samarium(II) iodide.

<span class="mw-page-title-main">Magnet</span> Object that has a magnetic field

A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, steel, nickel, cobalt, etc. and attracts or repels other magnets.

<span class="mw-page-title-main">Coercivity</span> Resistance of a ferromagnetic material to demagnetization by an external magnetic field

Coercivity, also called the magnetic coercivity, coercive field or coercive force, is a measure of the ability of a ferromagnetic material to withstand an external magnetic field without becoming demagnetized. Coercivity is usually measured in oersted or ampere/meter units and is denoted HC.

<span class="mw-page-title-main">Alnico</span> Family of iron alloys

Alnico is a family of iron alloys which, in addition to iron are composed primarily of aluminium (Al), nickel (Ni), and cobalt (Co), hence the acronym al-ni-co. They also include copper, and sometimes titanium. Alnico alloys are ferromagnetic, and are used to make permanent magnets. Before the development of rare-earth magnets in the 1970s, they were the strongest permanent magnet type. Other trade names for alloys in this family are: Alni, Alcomax, Hycomax, Columax, and Ticonal.

<span class="mw-page-title-main">Magnetic hysteresis</span> Application of an external magnetic field to a ferromagnet

Magnetic hysteresis occurs when an external magnetic field is applied to a ferromagnet such as iron and the atomic dipoles align themselves with it. Even when the field is removed, part of the alignment will be retained: the material has become magnetized. Once magnetized, the magnet will stay magnetized indefinitely. To demagnetize it requires heat or a magnetic field in the opposite direction. This is the effect that provides the element of memory in a hard disk drive.

Bismanol is an magnetic alloy of bismuth and manganese developed by the US Naval Ordnance Laboratory.

A samarium–cobalt (SmCo) magnet, a type of rare-earth magnet, is a strong permanent magnet made of two basic elements: samarium and cobalt.

<span class="mw-page-title-main">Rare-earth magnet</span> Strong permanent magnet made from alloys of rare-earth elements

A rare-earth magnet is a strong permanent magnet made from alloys of rare-earth elements. Developed in the 1970s and 1980s, rare-earth magnets are the strongest type of permanent magnets made, producing significantly stronger magnetic fields than other types such as ferrite or alnico magnets. The magnetic field typically produced by rare-earth magnets can exceed 1.2 teslas, whereas ferrite or ceramic magnets typically exhibit fields of 0.5 to 1 tesla.

<span class="mw-page-title-main">Ferrite (magnet)</span> Ferrimagnetic ceramic material composed of iron(III) oxide and a divalent metallic element

A ferrite is one of a family of iron oxide-containing magnetic ceramic materials. They are ferrimagnetic, meaning they are attracted by magnetic fields and can be magnetized to become permanent magnets. Unlike many ferromagnetic materials, most ferrites are not electrically conductive, making them useful in applications like magnetic cores for transformers to suppress eddy currents.

A magnetic alloy is a combination of various metals from the periodic table such as ferrite that exhibits magnetic properties such as ferromagnetism. Typically the alloy contains one of the three main magnetic elements : iron (Fe), nickel (Ni), or cobalt (Co). However, alloys such as Heusler alloys exhibit ferromagnetic properties without any of the preceding 3 elements, and alloys of iron and manganese such as stainless steels may be essentially nonmagnetic at room temperature. Magnetic properties of an alloy are highly dependent not only on the composition but also on heat treatment and mechanical processing.

A MEMS magnetic actuator is a device that uses the microelectromechanical systems (MEMS) to convert an electric current into a mechanical output by employing the well-known Lorentz Force Equation or the theory of Magnetism.

An electropermanent magnet or EPM is a type of permanent magnet in which the external magnetic field can be switched on or off by a pulse of electric current in a wire winding around part of the magnet. The magnet consists of two sections, one of "hard" magnetic material and one of "soft" material. The direction of magnetization in the latter piece can be switched by a pulse of current in a wire winding about the former. When the magnetically soft and hard materials have opposing magnetizations, the magnet produces no net external field across its poles, while when their direction of magnetization is aligned the magnet produces an external magnetic field.

<span class="mw-page-title-main">Tetrataenite</span> Native metal

Tetrataenite is a native metal alloy composed of chemically-ordered L10-type FeNi, recognized as a mineral in 1980. The mineral is named after its tetragonal crystal structure and its relation to the iron-nickel alloy, taenite, which is chemically disordered (A1) phase with an underlying fcc lattice. Tetrataenite is one of the mineral phases found in meteoric iron. Before its discovery in meteoritic samples, experimental synthesis of the L10 phase was first reported in 1962 by Louis Néel and co-workers, following neutron irradiation of a chemically disordered FeNi sample under an applied magnetic field. Compared to the magnetically soft, chemically disordered A1 phase (taenite), the tetragonal L10 structure of tetrataenite leads to good hard magnetic properties, including a large uniaxial magnetocrystalline anisotropy energy. Consequently, it is under consideration for applications as a rare-earth-free permanent magnet.

<span class="mw-page-title-main">Exchange spring magnet</span>

An exchange spring magnet is a magnetic material with high coercivity and high saturation properties derived from the exchange interaction between a hard magnetic material and a soft magnetic material, respectively.

<span class="mw-page-title-main">Masato Sagawa</span> Japanese scientist and entrepreneur

Masato Sagawa is a Japanese scientist and entrepreneur, and the inventor of the sintered permanent neodymium magnet (NdFeB). Sagawa was awarded the Japan Prize and IEEE Medal for Environmental and Safety Technologies for his efforts.

<span class="mw-page-title-main">Permanent magnet motor</span> Type of electric motor

A permanent magnet motor is a type of electric motor that uses permanent magnets for the field excitation and a wound armature. The permanent magnets can either be stationary or rotating; interior or exterior to the armature for a radial flux machine or layered with the armature for an axial flux topology. The schematic shows a permanent magnet motor with stationary magnets outside of a brushed armature.

References

  1. 1 2 Fraden, Jacob (2010). Handbook of Modern Sensors: Physics, Designs, and Applications, 4th Ed. USA: Springer Publishing. p. 73. ISBN   978-1-4419-6465-6.
  2. ↑ "What is a Strong Magnet?". The Magnetic Matters Blog. Adams Magnetic Products. October 5, 2012. Archived from the original on March 26, 2016. Retrieved October 12, 2012.
  3. 1 2 3 4 5 6 Lucas, Jacques; Lucas, Pierre; Le Mercier, Thierry; et al. (2014). Rare Earths: Science, Technology, Production and Use. Elsevier. pp. 224–225. ISBN   978-0-444-62744-5.
  4. ↑ M. Sagawa; S. Fujimura; N. Togawa; H. Yamamoto; Y. Matsuura (1984). "New material for permanent magnets on a base of Nd and Fe (invited)". Journal of Applied Physics. 55 (6): 2083. Bibcode:1984JAP....55.2083S. doi:10.1063/1.333572.
  5. ↑ J. J. Croat; J. F. Herbst; R. W. Lee; F. E. Pinkerton (1984). "Pr-Fe and Nd-Fe-based materials: A new class of high-performance permanent magnets (invited)". Journal of Applied Physics . 55 (6): 2078. Bibcode:1984JAP....55.2078C. doi:10.1063/1.333571.
  6. ↑ "What are neodymium magnets?". wiseGEEK website. Conjecture Corporation. 2011. Retrieved October 12, 2012.
  7. 1 2 Sintered NdFeB Magnets, What are Sintered NdFeB Magnets?
  8. ↑ Bonded NdFeB Magnets, What are Bonded NdFeB Magnets?
  9. 1 2 3 Chu, Steven. Critical Materials Strategy United States Department of Energy , December 2011. Accessed: 23 December 2011.
  10. ↑ Peter Robison & Gopal Ratnam (29 September 2010). "Pentagon Loses Control of Bombs to China Metal Monopoly". Bloomberg News . Retrieved 24 March 2014.
  11. ↑ "Research Funding for Rare Earth Free Permanent Magnets". ARPA-E. Archived from the original on 10 October 2013. Retrieved 23 April 2013.
  12. ↑ Overland, Indra (2019-03-01). "The geopolitics of renewable energy: Debunking four emerging myths". Energy Research & Social Science. 49: 36–40. Bibcode:2019ERSS...49...36O. doi: 10.1016/j.erss.2018.10.018 . hdl: 11250/2579292 . ISSN   2214-6296.
  13. ↑ "Magnetic Anisotropy". Hitchhiker's Guide to Magnetism. Retrieved 2 March 2014.
  14. ↑ Boysen, Earl; Muir, Nancy C. (2011). Nanotechnology For Dummies, 2nd Ed. John Wiley and Sons. p. 167. ISBN   978-1-118-13688-1.
  15. 1 2 As hybrid cars gobble rare metals, shortage looms, Reuters, August 31, 2009.
  16. ↑ Typical Physical and Chemical Properties of Some Magnetic Materials, Permanent Magnets Comparison and Selection.
  17. ↑ Drak, M.; Dobrzanski, L.A. (2007). "Corrosion of Nd-Fe-B permanent magnets" (PDF). Journal of Achievements in Materials and Manufacturing Engineering. 20 (1–2). Archived from the original (PDF) on 2012-04-02.
  18. ↑ Gauder, D. R.; Froning, M. H.; White, R. J.; Ray, A. E. (15 April 1988). "Elevated temperature study of Nd-Fe-B–based magnets with cobalt and dysprosium additions". Journal of Applied Physics. 63 (8): 3522–3524. Bibcode:1988JAP....63.3522G. doi:10.1063/1.340729.
  19. ↑ How to Understand the Grade of Sintered NdFeB Magnet?, Grades of Sintered NdFeB Magnets
  20. ↑ "Magnet Grade Chart". Amazing Magnets, LLC. Archived from the original on March 13, 2016. Retrieved December 4, 2013.
  21. ↑ "Neodymium Magnet Grades". totalElement. Retrieved 10 May 2023.
  22. ↑ "Grades of Neodymium magnets" (PDF). Everbeen Magnet. Retrieved December 6, 2015.
  23. ↑ "Grades of Neodymium". Archived from the original on 2024-05-26.
  24. ↑ "Manufacturing Process of Sintered Neodymium Magnets". American Applied Materials Corporation. Archived from the original on 2015-05-26.
  25. ↑ "Bonded Magnets – Production". Allstar Magnetics. Retrieved 26 October 2018.
  26. ↑ Bonded neo powder
  27. ↑ "World's First Magnetic Field Orientation Controlling Neodymium Magnet". Nitto Denko. 24 August 2015. Archived from the original on 9 October 2015. Retrieved 28 September 2015.
  28. ↑ "Potent magnet that can be molded like clay developed". Asahi Shimbun. 28 August 2015. Archived from the original on 28 September 2015. Retrieved 28 September 2015.
  29. ↑ "The Permanent Magnet Market – 2015" (PDF). Magnetics 2013 Conference. February 7, 2013. Retrieved November 28, 2013.
  30. ↑ Isaak, Adam (October 19, 2018). "A rare metal called neodymium is in your headphones, cellphone and electric cars like Tesla's Model 3 — and China controls the world's supply". CNBC.
  31. ↑ "How its made - Neodymium magnets كيفية صناعة المغناطيسات الخارقة القوة". 9 November 2014. Archived from the original on 2021-12-21 – via www.youtube.com.
  32. ↑ "Industrial Magnets strength and design for process protections - PowderProcess.net".
  33. ↑ "Options Guide". United Parachute Technologies. Archived from the original on July 17, 2011.
  34. ↑ O'Donnell, Jayne (July 26, 2012). "Feds file suit against Buckyballs, retailers ban product". USA Today .
  35. ↑ "Health Canada to ban the sale of 'Buckyballs' magnets". CTVNews. 2013-04-16. Retrieved 2018-08-22.
  36. ↑ "CPSC Approves New Federal Safety Standard for Magnets to Prevent Deaths and Serious Injuries from High-Powered Magnet Ingestion".
  37. ↑ Elster, Allen D. "MRI magnet design". Questions and Answers in MRI. Retrieved 2018-12-26.
  38. ↑ "TAVAC Safety and Effectiveness Analysis: LINX® Reflux Management System". Archived from the original on 2014-02-14.
  39. ↑ "The linx reflux management system: stop reflux at its source". Torax Medical Inc. Archived from the original on 2016-03-15. Retrieved 2014-05-18.
  40. ↑ Dvorsky, George (17 July 2013). "What You Need to Know About Getting Magnetic Finger Implants" . Retrieved 2016-09-30.
  41. ↑ I.Harrison, K.Warwick and V.Ruiz (2018), "Subdermal Magnetic Implants: An Experimental Study", Cybernetics and Systems, 49(2), 122-150.
  42. ↑ Marchio, Cathy (Apr 16, 2024). "Top 8 Uses for Neodymium Magnets". Stanford Magnets. Retrieved June 28, 2024.
  43. ↑ Pearson (2009). "Chapter 12: Magnetism". IIT Foundations - Physics. Pearson Education India. p. 505. ISBN   9788131728468.
  44. ↑ "Magnetic Crane". Yuantai Crane. Retrieved June 28, 2024.
  45. ↑ Swain, Frank (March 29, 2018). "How to remove a finger with two super magnets". The Sciencepunk Blog. Seed Media Group LLC. Retrieved 2009-06-28.
  46. ↑ "Warning issued around the ingestion of 'super strong' neodymium magnets often found in toys". NursingNotes. 2021-05-21. Retrieved 2021-05-27.
  47. ↑ "CPSC Safety Alert: Ingested Magnets Can Cause Serious Intestinal Injuries" (PDF). U.S. Consumer Product Safety Commission. Archived from the original (PDF) on 8 January 2013. Retrieved 13 December 2012.

Further reading

This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.