(2N) 99% • (3N) 99.9% • (4N) 99.99% • (5N) 99.999% • (6N) 99.9999%
RARE EARTHS INFORMATION CENTER
AE Rare Earths™
What are the rare earths?
The rare earth or lanthanide elements (REEs) are a group of 17 metals with unique properties composed of lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, and promethium. Scandium and yttrium are also sometimes included in this group in that they share many properties. They appear similar to the transition metals (silvery metallic), and find many diverse applications.
Despite their name, rare earths are actually abundant in the earth's crust, though the extraction and refining process is complicated and costly. Rare earths are divided into two categories based on their weight and atomic numbers: Light rare earth elements (LREEs, or ceric rare earths) include lanthanum, cerium, praseodymium, promethium, neodymium and samarium, along with scandium; heavy rare earth elements (HREEs, or yttric rare earths) include europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium, as well as yttrium. HREEs are more abundant than LREEs and more complex to mine.
Lanthanum is the first element in the rare earth or lanthanide series. It is the model for all the other trivalent rare earths. After cerium, it is the second most abundant of the rare earths. Lanthanum is available as metal and compounds with purities from 99% to 99.999% (ACS grade to ultra high purity); metals in the form of foil, sputtering target, and rod, and compounds as submicron and nanopowder.Lanthanum-rich lanthanide compositions have been used extensively for cracking reactions in FCC catalysts, especially to manufacture low-octane fuel for heavy crude oil. Lantahanum is found in monazite and bastnasite. The name Lanthanum originates from the Greek word Lanthaneia which means 'To lie hidden'. It is utilized in green phosphors based on the aluminate (La0.4Ce0.45Tb0.15)PO4. Lanthanide zirconates and lanthanum strontium manganites are used for their catalytic and conductivity properties and lanthanum stabilized zirconia has useful electrical and mechanical properties. Lanthanum's ability to bind with phosphates in water creates numerous uses in water treatment. It is utilized in laser crystals based on the yttrium-lanthanum-fluoride (YLF) composition.
Cerium is the most abundant of the rare earths. It is characterized chemically by having two valence states , the +3 cerous and +4 ceric states. Cerium is available as metal and compounds with purities from 99% to 99.999% (ACS grade to ultra high purity); metals in the form of foil, sputtering target, and rod, and compounds as submicron and nanopowder. The ceric state is the only non-trivalent rare earth ion stable in aqueous solutions.It is, therefore, strongly acidic and moderately toxic. It is also a strong oxidizer.The cerous state closely resembles the other trivalent rare earths. The numerous commercial applications for cerium include metallurgy, glass and glass polishing, ceramics, catalysts, and in phosphors. In steel manufacturing it is used to remove free oxygen and sulfur by forming stable oxysulfides and by tying up undesirable trace elements, such as lead and antimony. It is considered to be the most efficient glass polishing agent for precision optical polishing. It is also used to decolor glass by keeping iron in its ferrous state. The ability of cerium-doped glass to block out ultra violet light is utilized in the manufacturing of medical glassware and aerospace windows. It is also used to prevent polymers from darkening in sunlight and to suppress discoloration of television glass. It is applied to optical components to improve performance. Cerium is also used in a variety of ceramics, including dental compositions and as a phase stabilizer in zirconia-based products. Ceria plays several catalytic roles. In catalytic converters it acts as a stabilizer for the high surface area alumina, as a promoter of the water-gas shift reaction, as an oxygen storage component and as an enhancer of the NOX reduction capability of Rhodium. Cerium is added to the dominant catalyst for the production of styrene from ethylbenezene to improve styrene formation. It is used in FCC catalysts containing zeolites to provide both catalytic reactivity in the reactor and thermal stability in the regenerator.
Praseodymium resembles the typical trivalent rare earths, however, it will exhibit a +4 state when stabilized in a zirconia host. Praseodymium is available as metal and compounds with purities from 99% to 99.999% (ACS grade to ultra-high purity); metals in the form of foil, sputtering target, and rod, and compounds as submicron and nanopowder. The element is found in most all light rare earth derivatives. It is highly valued in glass and ceramic production as a bright yellow pigment because of its optimum reflectance at 560 nm. Much research is being done on its optical properties for use in amplification of telecommunication systems, including as a doping agent in fluoride fibers. Praseodymium doped zirconia is a potential cathode for low temperature Solid Oxide Fuel Cell applications. It is also used in the scintillator for medical CAT scans.
Neodymium is the most abundant of the rare earths after cerium and lanthanum. Neodymium is available as metal and compounds with purities from 99% to 99.999% (ACS grade to ultra-high purity); metals in the form of foil, sputtering target, and rod, and compounds as submicron and nanopowder. Neodymium is a Block F, Group 3, Period 6 element. The number of electrons in each of Neodymium's shells is 2, 8, 18, 22, 8, 2 and its electronic configuration is [Xe] 4f4 6s2. In its elemental form neodymium's CAS number is 7440-00-8. The neodymium atom has a radius of 181.4.pm and it's Van der Waals radius is 181.pm. Neodymium is the most abundant of the rare earths after cerium and lanthanum. Neodymium is available as metal and compounds with purities from 99% to 99.999% (ACS grade to ultra-high purity); metals in the form of foil, sputtering target, and rod, and compounds as submicron and nanopowder. Primary applications include lasers, glass coloring and tinting, dielectrics and, most importantly, as the fundamental basis for neodymium-iron-boron permanent magnets. Neodymium has a strong absorption band centered at 580 nm, which is very close to the human eye's maximum level of sensitivity making it useful in protective lenses for welding goggles. It is also used in CRT displays to enhance contrast between reds and greens and highly valued in glass manufacturing for its attractive purple coloring. Neodymium is included in many formulations of barium titanate, used as dielectric coatings and in multi-layer capacitors essential to electronic equipment. Neodymium is found in monazite and bastnäsite ores. Neodymium was first discovered by Carl Aer von Welsbach in 1885. Neodymium is found in monazite and bastnäsite ores. Neodymium was first discovered by Carl Aer von Welsbach in 1885. It is also used in CRT displays to enhance contrast between reds and greens and highly valued in glass manufacturing for its attractive purple coloring. Neodymium is included in many formulations of barium titanate, used as dielectric coatings and in multi-layer capacitors essential to electronic equipment.
Promethium is a Block F, Group 3, Period 6 element. The number of electrons in each of Promethium's shells is 2, 8, 18, 23, 8, 2 and its electronic configuration is [Xe] 4f5 6s2. In its elemental form promethium's CAS number is 7440-12-2. The promethium atom has a radius of 183.4.pm and it's Van der Waals radius is 200.pm.
Samarium is primarily utilized in the production of samarium-cobalt (Sm2Co17) permanent magnets. Samarium is available as metal and compounds with purities from 99% to 99.999% (ACS grade to ultra-high purity); metals in the form of foil, sputtering target, and rod, and compounds as submicron and nanopowder. It is also used in laser applications and for its dielectric properties. Samarium-cobalt magnets replaced the more expensive platinum-cobalt magnets in the early 1970s. While now overshadowed by the less expensive neodymium-iron-boron magnet, they are still valued for their ability to function at high temperatures. They are utilized in lightweight electronic equipment where size or space is a limiting factor and where functionality at high temperature is a concern. Applications include electronic watches, aeospace equipment, microwave technology and servomotors. Because of its weak spectral absorption band samarium is used in the filter glass on Nd:YAG solid state lasers to surround the laser rod to improve efficiency by absorbing stray emissions. Samarium forms stable titanate compounds with useful dielectric properties suitable for coatings and in capacitors at microwave frequencies.
Europium is utilized primarily for its unique luminescent behavior. Europium is available as metal and compounds with purities from 99% to 99.999% (ACS grade to ultra-high purity); metals in the form of foil, sputtering target, and rod, and compounds as submicron and nanopowder. Excitation of the Europium atom by absorption of ultra violet radiation can result in specific energy level transitions within the atom creating an emission of visible radiation.In energy efficient fluorescent lighting, Europium provides not only the necessary red, but also the blue. Several commercial blue phosphors are based on Europium. Its luminesence is also valuable in medical, surgical and biochemical applications.
Gadolinium is utilized for both its high magnetic moment (7.94µB) and in phosphors and scintillator material. When complexed with EDTA ligands, it is used as an injectable contrast agent for patients undergoing magnetic resonance imaging. Gadolinium is available as metal and compounds with purities from 99% to 99.999% (ACS grade to ultra-high purity); metals in the form of foil, sputtering target, and rod, and compounds as submicron and nanopowder. With its high magnetic moment, gadolinium can reduce relaxation times and thereby enhance signal intensity. The extra stable half-full 4f electron shell with no low lying energy levels creates applications as an inert phosphor host. Gadolinium can therefore act as hosts for x-ray cassettes and in scintillator materials for computer tomography.
Terbium is primarily used in phosphors, particularly in fluorescent lamps and as the high intensity green emitter used in projection televisions, such as the yttrium-aluminum-garnet (Tb:YAG) variety. Terbium is available as metal and compounds with purities from 99% to 99.999% (ACS grade to ultra-high purity); metals in the form of foil, sputtering target, and rod, and compounds as submicron and nanopowder. Terbium responds efficiently in x-ray excitation and is, therefore, used as an x-ray phosphor. Terbium alloys are also used in magneto-optic recording films, such as Tb-Fe-Co.
Dysprosium is most commonly used in neodymium-iron-boron high strength permanent magnets. Dysprosium is available as metal and compounds with purities from 99% to 99.999% (ACS grade to ultra-high purity); metals in the form of foil, sputtering target, and rod, and compounds as submicron and nanopowder. While it has one of the highest magnetic moments of any of the rare earths (10.6µB), this has not resulted in an ability to perform on its own as a practical alternative to neodymium compositions. It is however now an essential additive in NdFeB production. It is also used in special ceramic compositions based on BaTiO formulations. Recent research has examined the use of dysprosium in dysprosium-iron-garnet (DyIG) and silicon implanted with dysprosium and holmium to form donor centers. Dysprosium is added to various advanced optical formulations due to the fact that it emits in the 470-500 and 570-600 nm wavelengths.
Holmium has the highest magnetic moment (10.6µB) of any naturally occurring element. Because of this it has been used to create the highest known magnetic fields by placing it within high strength magnets as a pole piece or magnetic flux concentrator. This magnetic property also has value in yttrium-iron-garnet (YIG) lasers for microwave equipment. Holmium is available as metal and compounds with purities from 99% to 99.999% (ACS grade to ultra-high purity); metals in the form of foil, sputtering target, and rod, and compounds as submicron and nanopowder. Holmium lases at a human eye safe 2.08 microns allowing its use in a variety of medical and dental applications in both yttrium-aluminum-garnet (YAG) and yttrium-lanthanum-fluoride (YLF) solid state lasers. The wavelength allows for use in silica fibers designed for shorter wavelengths while still providing the cutting strength of longer wave length equipment.
Erbium has application in glass coloring, as an amplifier in fiber optics, and in lasers for medical and dental use. Erbium is available as metal and compounds with purities from 99% to 99.999% (ACS grade to ultra-high purity); metals in the form of foil, sputtering target, and rod, and compounds as submicron and nanopowder. The ion has a very narrow absorption band coloring erbium salts pink. It is therefore used in eyeware and decorative glassware. It can neutralize discoloring impurities such as ferric ions and produce a neutral gray shade. It is used in a variety of glass products for this purpose. It is particularly useful as an amplifier for fiber optic data transfer. Erbium lases at the wavelength required to provide an efficient optical method of amplification, 1.55 microns. Lasers based on Er:YAG are ideally suited for surgical applications because of its ability to deliver energy without thermal build-up in tissue.
Thulium is representative of the other lanthanides (rare earths) similar in chemistry to Yttrium. Thulium is available as metal and compounds with purities from 99% to 99.999% (ACS grade to ultra-high purity); metals in the form of foil, sputtering target, and rod, and compounds as submicron and nanopowder. Tm emits blue upon excitation. Flat panel screens depend critically on bright blue emitters. Also, under X-ray bombardment emissions are in both the 375 nm (ultra violet) and 465 (visible blue) wave lengths. This gives the material useful applications in low radiation detection for detection badges and similar uses. It is also used in other luminescence applications, such as halide discharge lamps. Flat panel screens depend critically on bright blue emitters.
Ytterbium is being applied to numerous fiber amplifier and fiber optic technologies and in various lasing applications. Ytterbium is found in monazite sand as well as the ores euxenite and xenotime and is available as metal and compounds with purities from 99% to 99.999% (ACS grade to ultra-high purity); metals in the form of foil, sputtering target, and rod, and compounds as submicron and nanopowder. It has a single dominant absorption band at 985 in the infra-red making it useful in silicon photocells to directly convert radiant energy to electricity. Ytterbium metal increases its electrical resistance when subjected to very high stresses. This property is used in stress gauges for monitoring ground deformations from earthquakes and nuclear explosions. It is also used in thermal barrier system bond coatings on nickel, iron and other transitional metal alloy substrates. The name Ytterbium originates after the name for the Swedish village of Ytterby.
Lutetium is the last member of the rare earth series. Lutetium is available as metal and compounds with purities from 99% to 99.999% (ACS grade to ultra-high purity); metals in the form of foil, sputtering target, and rod, and compounds as submicron and nanopowder. Unlike most rare earths it lacks a magnetic moment. It also has the smallest metallic radius of any rare earth. It is perhaps the least naturally abundant of the lanthanides. It is the ideal host for x-ray phosphors because it produces the densest known white material, lutetium tantalate (LuTaO4). It is utilized as a dopant in matching lattice parameters of certain substrate garnet crystals, such as indium-gallium-garnet (IGG) crystals due its lack of a magnetic moment.
How are the rare earths produced? Elemental rare earths are produced through the separation of certain rare earth oxide (REO)-bearing minerals, including bastnazite, monazite and ionic clays. Mined bastnazite is processed to a rare earth concentrate, which is separated by solvent extraction into individual rare earth chlorides or nitrates depending on the system. These rare earth chloride or nitrate concentrates are subsequently refined to a variety of rare earth compounds such as oxides, carbonates and fluorides. Rare Earth metal is produced through the thermic reduction of that element's oxide or fluoride powder.
Where are the global locations of rare earths deposits? A vast majority of the world's producing reserves of rare earth minerals are located in Northern and Southern China, where American Elements operates a rare earth separations plant. In China, an oft quoted statement of former Communist leader Deng Xiao Ping is that "the Middle East has oil, and Baotou has rare earths." 80% of Chinese production is concentrated in Northern China (Baotou, Inner Mongolia), which yields light rare earth elements; proven bastnazite reserves in the north have been estimated to be 48 million metric tons, with prospective reserves estimated to be another 120 million metric tons. In the south, heavy rare earths are mined from ion adsorption clays located in the provinces of Jiangxi and Guangdong.
Outside of China, other rare earth deposits are located in the United States (bastnazite), Australia (monazite, carbonatites, and and xenotime), India and South Africa, Kazakhstan, Uzbekistan and Ukraine (ioparite and apatite), Canada (apatite and allamite). Historically, most of these regions have not exploited their reserves; this is increasingly no longer the case, for reasons discussed further below.
Australia has monozite deposits in Western Australia as a byproduct of their zirconium and titanium production from heavy mineral sands. In the early 1990's Australia produced a substantial quantity of monozite for export to rare earth separation plants in Asia and Europe. However, production essentially stopped in 1994 due to the problems associated with the disposal of radioactive thorium (a monozite bi-product). There have been several proposals to develop deposits in Western Australia, such as the Mt. Weld deposit in Pinjarra.
Brazil also has large monozite deposits in beach sands on the northeast coast of the country. Brazil has several facilities that produce relatively small quantities of separated rare earths. Since 1997, there has been a plan to separate rare earths from a stockpile of monozite at Industrias Nucleares do Brasil's former mining and milling complex with the intent to store the extracted thorium as fuel for nuclear power plants. There are no current large commercial producers in Brazil.
India is currently the largest monozite producer from beach sands along the coast of Kerala and Tamil Nadu. Producers export monozite concentrate, mixed rare earth Chlorides and oxides.
Russia. Several small rare earth processing facilities exist in Russia which process from loparite and apatite deposits in Kazakstan, Uzebekistan and Ukraine. Operations are sporadic and production is usually available only on a spot sale basis.
South Africa has been planning since 1998 to start up production of monozite from the Steenkampskaal mine in the Western Cape province. Estimated reserves are 250,000 metric tons.
United States. Until 1998, the United States was the second largest producer of rare earths from the Molycorp mine in Mountain Pass, California. The facility was closed in December 1998 due to certain environmental concerns. In 2000, Unocal sold the Molycorp Mine to Chevron, who spun it off into a subsidiary corporation called "Chevron Mining". This company was taken public in 2008 as Molycorp. In 2011, the mine re-opened and began producing in small quantity. Molycorp first purchased the metal reduction operations owned by Santoku in Arizona to execute on its new "Mines to Magnets" strategy to completely control the process of producing NdFeB magnet alloy from the mine. Molycorp then purchased Boulder Wind Power which requires NdFeB magnets in their assembly. In March of 2012, Molycorp announced it had acquired Neo Technologies, the holder of the Magnequench patent for producing NdFeB alloy.
American Elements' Rare Earth Production. American Elements maintains the world's largest catalogue of rare earth materials, including metals, compounds, nanoparticles and ultra high purity forms. American Elements' Chinese production facility is one of only a few major rare earth separations plants in Baotou with warehouse and shipping facilities at the port in Tianjin. The facility produces under ISO 9002 certification.
As a major Baotou-based producer, American Elements maintains close working relationships with the key city, state and national Chinese government officials controlling both mineral availability and separated rare earth exportation. Our quota allocation is timely granted and more than sufficient to allow for required sales. We will often have early information on the intentions of government officials and some limited ability to provide input in these areas. By producing close to the mineral source, transportation costs are minimized.
Rare Earth History and Historical Pricing. The history of rare earth use in industry began in the 1950's with the invention of the television which required europium as the phosphor. In the 1960's discoveries were made which created applications for the two rare earth elements that make up over 50% of the bastnazite ore body; cerium and lanthanum. These elements found uses primarily in glass production and production of various catalysts.
The rare earths began to achieve global commoditized pricing in 1987 when large scale prices were first established as a result of the initial commercialization of the NdFeB magnet. Prices steadily rose until around Q2 1989. Stimulated by these relatively high prices and forecasts of 100%+ annual growth, Chinese rare earth separation plants rapidly expanded output capacity resulting in over capacity and price declines through 1992, which was also influenced by a concurrent recession in the global computer market. By Q4 1992 a combination of (1) plants closing that could not compete in this market environment and (2) exponential growth in NdFeB alloy demand, caused a supply shortage. Prices again recovered, steadily rising from Q1 1993 through Q1 1996. However, as early as the end of 1994, Chinese rare earth producers again rapidly increased capacity with, in our estimate, supply actually exceeding demand as early as Q3 1995.
As prices began to again fall at the beginning of 1996, an effort was initiated by Chinese government agencies to cause producers to voluntarily reduce production to within the projected demand with the stated goal of Chinese officials to establish a continuing "reasonable price" range. This voluntary program was under the threat that China would take a direct hand to control production output and exportation, if voluntary measures were insufficient. However, prices continued to fall through Q3 1999 when Chinese officials announced that export licenses would soon be required for all rare earth product exports. First to respond to this was Japanese buyers who purchased substantial inventories commencing Q4 1999 causing prices to steadily increase.
Prices were additionally impacted by the 1999 closure of the only large scale rare earth mine outside of China; the Mountain Pass mine owned by Molycorp (see above).
In Q2 of 2000, China in fact implemented its export license system granting each producer and certain Chinese import/export companies with quarterly export quota limits based somewhat arbitrarily on a combination of historical volume and a government desire to close many small facilities and reduce the number of ionic clay processors in Southern China in favor of production from Baotou. Additionally, China ordered a production stoppage at many ionic clay mines in Southern China, such that now substantially all rare earth mineral supplies for both exportation and domestic consumption come from Baotou.
Rare Earth Trends and Pricing. The forgoing efforts by China to increase and stabilize rare earth prices had only marginal effect. The desire of the central government to continue to collect U.S. currency acted as a countervailing balance. However, in 2005 China first indicated that it was placing a greater emphasize on retaining its raw material resources than continuing to build its cash reserves. This lead to a serious effort to restrict rare earth exports and thereby increase prices.
In 2006, the government issued its first of currently two 10% export tariffs on rare earths. Additionally, it began to strict the amount of quarterly export quota granted to producers to a very small percentage of the quotas first issued in 2005. In 2008, these factors forced rare earth prices even higher with lower grade forms potentially becoming scarce further in the future. In 2009 and 2010, China continued to close down facilities and consolidate production. The tariffs were further increased. In 2010, China refused to ship rare earths to Japan in response to the arrest of a shipping captain in the East China Sea. Since then, the world has become much more focused on rare earths. Conferences in March 2012 in Europe (Euromines) and Washington DC (TREM12) discussed the world response. In March 2012, the U.S., Japan and EU also filed a WTO action against China for violating its WTO agreement for handling commodity production.
Forms of Rare Earths. American Elements manufactures the world's largest catalogue of rare earth materials in forms including metals, oxides, nanoparticles and nanopowders, compound powders and solutions, and organometallics.
Rare Earth Metals can be purchased in numerous forms for alloying, for use in coating and thin film Chemical Vapor Deposition (CVD) and Physical Vapor Deposition (PVD) processes including Thermal and Electron Beam (E-Beam) Evaporation, Low Temperature Organic Evaporation, Atomic Layer Deposition (ALD), Organometallic and Chemical Vapor Deposition (MOCVD) for specific applications such as fuel cells and solar energy.
Rare Earth Oxides are available in many forms including pellets and targets for coating and thin film Chemical Vapor Deposition (CVD) and Physical Vapor Deposition (PVD) processes including Thermal and Electron Beam (E-Beam) Evaporation and powders for ceramic applications.
Rare Earth Compounds are available as powders in all of the standard compound forms for uses were a soluble form of the rare earth is needed or in the case of the fluorides (which are insoluble) in situations where oxygen is not desirable, such in metal alloy production and certain optical applications.
Rare Earth Solutions of each of the forgoing rare earth compounds are produced by American Elements' AE Solutions division in both research and commercial (bulk) quantities.
Rare Earth Organometallics provide a rare earth source that is soluble in non-aqueous (organic) solvents. A brief list of the organometallic rare earths produced by American Elements are listed below.
Recent Research & Development for Rare Earths
- Toshiyuki Masui, Naoki Takeuchi, Hiroki Nakado, Nobuhito Imanaka, Novel environment-friendly green pigments based on rare earth cuprate, Dyes and Pigments, Volume 113, February 2015
- Giable George, The structural and optical studies of titanium doped rare earth pigments and coloring applications, Dyes and Pigments, Volume 112, January 2015
- Mingyue Zhao, Zhangjian Zhou, Qingming Ding, Ming Zhong, Kameel Arshad, Effect of rare earth elements on the consolidation behavior and microstructure of tungsten alloys, International Journal of Refractory Metals and Hard Materials, Volume 48, January 2015
- Dawn E. Janney, J. Rory Kennedy, James W. Madden, Thomas P. O’Holleran, Am phases in the matrix of a U–Pu–Zr alloy with Np, Am, and rare-earth elements, Journal of Nuclear Materials, Volume 456, January 2015
- A. Heidary Moghadam, V. Dashtizad, A. Kaflou, H. Yoozbashizadeh, Effect of rare earth elements on sorption characteristics of nanostructured Zr–Co sintered porous getters, Vacuum, Volume 111, January 2015
- Li Honglin, Lv Yingbo, Li Jinzhu, Yu Ke, Experimental and first-principles studies of structural and optical properties of rare earth (RE = La, Er, Nd) doped ZnO, Journal of Alloys and Compounds, Volume 617, 25 December 2014
- Poonam Pahuja, R.K. Kotnala, R.P. Tandon, Effect of rare earth substitution on properties of barium strontium titanate ceramic and its multiferroic composite with nickel cobalt ferrite, Journal of Alloys and Compounds, Volume 617, 25 December 2014
- X.J. Zhang, W.B. Mi, X.C. Wang, H.L. Bai, First-principles prediction of electronic structure and magnetic ordering of rare-earth metals doped ZnO, Journal of Alloys and Compounds, Volume 617, 25 December 2014
- Li Guo, Zhiqiang Zhou, Hongming Yuan, Hydrothermal synthesis and magnetic properties of Fe3+-doped multiferroic hexagonal rare-earth manganates, Journal of Alloys and Compounds, Volume 616, 15 December 2014
- P. Saravanan, V.T.P. Vinod, Miroslav Cerník, Dibyendu Chakravarty, P. Ghosal, S.V. Kamat, Exchange coupled rare-earth free Mn-Al/Fe nanocomposite magnets by spark plasma sintering, Materials Letters, Volume 137, 15 December 2014