Samarium
Samarium is a chemical element with symbol Sm and atomic number 62. It is a moderately hard silvery metal that readily oxidizes in air. Being a typical member of the lanthanide series, samarium usually assumes the oxidation state +3.
Identity
- Atomic mass
- 150.362 u
- Category
- Lanthanides
- Group
- 3
- Period
- 6
- Block
- f
- Oxidation States
- +2, +3
- Phase (25 °C)
- Solid
- Appearance
- silvery white
Electronic Structure
- Electron configuration
- 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f6
- Short configuration
- [Xe] 4f6 6s2
- Electrons per shell
- 2, 8, 18, 24, 8, 2
- Electronegativity (Pauling)
- 1.17
- Electron affinity
- 15.6 kJ/mol
- 1st ionization energy
- 545 kJ/mol
- Ionization energies
- 545 · 1070 · 2260 · 3990 kJ/mol
Physical properties
- Melting point
- 1071.8 °C (1345 K)
- Boiling point
- 1899.8 °C (2173 K)
- Density
- 7.52 g/cm³
- Molar heat capacity
- 29.5 J/(mol·K)
Chemical behavior of samarium
Samarium has six outer electrons ([Xe] 4f⁶ 6s²) and acts as +3, with a rare stable +2 in the iodide and the oxide SmO. Its electronegativity is very low (1.17) and it forms highly ionic bonds. It is hard, brittle and oxidizes in air forming a yellowish layer that flakes off. Its six unpaired f electrons generate the magnetism that, alloyed with cobalt, withstands extreme temperatures.
Reactivity
4 Sm + 3 O₂ → 2 Sm₂O₃
In air it becomes covered with a pale yellow oxide that does not protect the metal. When heated it burns to the oxide; fine powder can ignite spontaneously.
2 Sm + 6 H₂O → 2 Sm(OH)₃ + 3 H₂
It reacts slowly when cold and vigorously when hot, giving hydroxide and hydrogen. Sintered magnets resist better because of their cobalt matrix.
2 Sm + 6 HCl → 2 SmCl₃ + 3 H₂
It dissolves in dilute acids forming yellow samarium(III) salts. The chloride is the route to obtaining the metal by electrolysis.
Sm + I₂ → SmI₂
With iodine under controlled conditions it gives samarium(II) iodide, dark green, a highly regarded reducing agent in organic synthesis (Kagan's reagent).
Notable compounds
| Compound | Formula | Use or importance |
|---|---|---|
| Samarium–cobalt magnet | SmCo₅ | High-temperature motors and sensors |
| Samarium oxide | Sm₂O₃ | Catalysts and technical ceramics |
| Samarium(II) iodide | SmI₂ | Reducing agent in organic synthesis |
| Samarium chloride | SmCl₃ | Production of the metal and catalysts |
| Samarium hexaboride | SmB₆ | Topological insulator and quantum studies |
Electron shell distribution
View in the atom builderIsotopes
Natural samarium mixes seven isotopes: samarium-144 (¹⁴⁴Sm, ~3.1%), 147Sm (~15%), 148Sm (~11.2%), 149Sm (~13.8%), 150Sm (~7.4%), 152Sm (~26.7%) and 154Sm (~22.7%), all with 62 protons. 147Sm is a primordial radionuclide with a very long half-life, and the 147Sm/143Nd pair dates rocks and meteorites.
Occurrence and production
It appears at about 7 ppm in the crust, in bastnasite and monazite alongside neodymium and praseodymium. The main deposits are in China, the United States and Australia. It is obtained by acid dissolution, solvent extraction and ion exchange, and the metal by electrolysis of molten chlorides or reduction with lanthanum.
History and origin of the name
Paul-Émile Lecoq de Boisbaudran identified it in 1879 in samarskite and named it samarium, the first element baptized after a person: Colonel Samarsky, the Russian engineer who supplied the sample. Samarskite hid other lanthanides as well. Its magnetic hour came in the 1960s, when Strnat invented the SmCo₅ magnets.
Applications and relevance of samarium
Uses of the element
As SmCo₅ and Sm₂Co₁₇ alloys it forms magnets that work up to 300 °C without losing strength: aircraft motors, ABS brake sensors, couplings and military equipment. Its corrosion resistance avoids thick coatings.
Uses of its compounds
The oxide catalyzes the dehydration of alcohols and dopes ceramics; samarium(II) iodide reduces complex molecules in pharmaceuticals; Sm-153 (Quadramet) treats the pain of bone metastases. The hexaboride is a laboratory of quantum physics.
Health, safety and environment
Biological role
It has no biological function and its absorption is minimal. Medical Sm-153 is administered under hospital control and decays in days. Finished magnets do not release samarium in normal use.
Safety
Fine metal powder can burn in air and requires an inert atmosphere and extraction. The everyday risk is mechanical: powerful magnets that trap fingers or shatter on impact. Swallowing small pieces requires emergency medical care.
Environment
It shares the mining footprint of the rare earths: separation energy and waste containing thorium. Its use in efficient motors more than compensates, and SmCo magnets are recycled for their high cobalt and samarium value.
Frequently asked questions about Samarium
What is samarium used for in magnets?
Samarium is part of samarium–cobalt magnets, rare-earth permanent magnets highly valued when stability at high temperatures is needed. Although they do not reach the strength of neodymium magnets, they resist demagnetization better and keep their properties in demanding thermal conditions. They are used in motors, sensors, couplings, aerospace equipment and industrial applications where thermal reliability is a priority.
At what temperature can samarium–cobalt magnets work?
Samarium–cobalt magnets can routinely operate at temperatures well above those of many neodymium magnets. Depending on their composition and design, some grades allow operating temperatures close to 300 °C or even higher. This thermal stability makes them suitable for high-performance motors, industrial sensors, aerospace equipment and devices that cannot afford a significant loss of magnetic field due to heat.
Where does samarium come from?
Samarium is extracted from rare-earth minerals, especially bastnasite and monazite, where it appears mixed with other lanthanides. Its production requires crushing the ore, dissolving it and separating the elements through solvent extraction or ion exchange processes. It can then be obtained as an oxide or as a metal. The complexity of the separation is due to the fact that the lanthanides have very similar chemical properties among themselves.
What other uses does samarium have besides magnets?
Besides permanent magnets, samarium is used in special alloys, technical ceramics, catalysts and optical materials. Its compounds can be used in glasses and crystals to modify optical properties, as well as in scientific research and nuclear technology. It has also been studied in medicine for certain treatments with radioactive isotopes. Even so, its best-known and most commercially relevant application remains the manufacture of samarium–cobalt magnets.
What is the difference between samarium–cobalt and neodymium magnets?
Neodymium magnets are generally more powerful and cheaper, but they lose some of their performance when heated and need protection against corrosion. Samarium–cobalt magnets are less strong, but they keep their magnetism better at high temperatures and resist oxidation more effectively. That is why neodymium dominates in electronics and conventional motors, while samarium–cobalt is preferred in hot, corrosive or technically demanding environments.
Is samarium dangerous?
Metallic samarium can react with air and moisture, and handling it as powder or industrial material requires specific precautions. However, it is not an element present freely in everyday products: it appears built into magnets, alloys and technical components. For the general public, the main risk is usually not the element itself but the strength of samarium–cobalt magnets, which can cause pinch injuries or break if they are handled badly.
Why do samarium–cobalt magnets resist corrosion better?
The samarium–cobalt alloy has greater natural resistance to oxidation than neodymium–iron–boron magnets. This is due to its composition and internal structure, which are less prone to degrade in humid environments. Even so, in acidic, marine or very aggressive conditions a protective coating may be recommended. This resistance reduces the need for surface protection and favors its use in industrial equipment and demanding applications.
Main sources consulted: PubChem, Royal Society of Chemistry, NIST, IUPAC. Last revision: November 2026.