Today, let’s take a look at interesting facts about Samarium and answer the following questions: “Why Is Samarium Considered A Rare Earth Element?”, and “Why Is Samarium Considered A Critical Raw Material?”

Check out the rest of the light rare earth elements here – ‘20 Interesting Facts About The Light Rare Earth Elements (LREEs)’

Why Is Samarium Considered A Rare Earth Element?

Samarium is considered a rare earth element because it is one of the 15 lanthanide elements that form the core of the rare earth element group. Samarium has atomic number 62, placing it firmly within the lanthanide series that spans from lanthanum (atomic number 57) through lutetium (atomic number 71). As a lanthanide, samarium shares the characteristic chemical and physical properties that define this group, including a trivalent charge (Sm3+) and similar ionic radii to other rare earth elements. With a crustal abundance of 7.05 parts per million, samarium is more abundant than elements like silver, gold, or platinum, yet like other rare earth elements, it rarely forms concentrated ore deposits.

The chemical properties of samarium align perfectly with the defining characteristics of rare earth elements. Like all lanthanides, samarium exhibits the typical 3+ oxidation state and has an ionic radius that follows the systematic decrease known as “lanthanide contraction” – the progressive decrease in ionic radius from lanthanum to lutetium. This chemical similarity means samarium occurs naturally with other rare earth elements in the same mineral deposits. Samarium is found in the primary rare earth minerals including bastnäsite (REE)CO3F, monazite (REE,Th)PO4, and xenotime, where it occupies crystal lattice positions interchangeably with other rare earth elements. The REE-bearing minerals can accommodate samarium because “REEs can substitute for one another in crystal structures, and multiple REEs typically occur within a single mineral.”

Samarium’s classification as a light rare earth element (LREE) places it in the group spanning lanthanum through gadolinium (atomic numbers 57-64). This grouping is based on atomic weight and reflects both chemical behavior and typical occurrence patterns in ore deposits. In major rare earth deposits like Mountain Pass in California and Bayan Obo in China, samarium occurs as part of the LREE-dominated mineralization. For example, at Mountain Pass, the bastnäsite ore contains samarium at 0.79% of the total rare earth oxide content, while at Bayan Obo it comprises 0.80% of the total REO. These consistent occurrence patterns across different deposits demonstrate samarium’s integral membership in the rare earth element suite.

From an industrial perspective, samarium’s applications reinforce its rare earth element status. Samarium is essential for samarium-cobalt permanent magnets, which, though less powerful than neodymium magnets, “have better heat tolerance and are used in lieu of neodymium magnets where heat stress is an issue.” These magnets represent one of the major applications driving rare earth element demand. Samarium is also used in nuclear reactor control rods and lasers, applications that leverage its unique nuclear and optical properties characteristic of the lanthanides. Additionally, samarium is used alongside cerium, lanthanum, neodymium, and praseodymium in nickel-metal hydride batteries, demonstrating its functional grouping with other rare earth elements in practical applications. The combination of samarium’s position in the lanthanide series, its chemical properties, its consistent occurrence with other REEs in nature, and its industrial applications alongside other rare earth elements firmly establishes its classification as a rare earth element.

Why Is Samarium Considered A Critical Raw Material?

Samarium is considered a critical raw material due to its essential role in high-performance permanent magnets and strategic defense applications, combined with severe supply chain vulnerabilities. Samarium-cobalt magnets are irreplaceable in applications where high temperature resistance is required, as they “have better heat tolerance and are used in lieu of neodymium magnets where heat stress is an issue.” These magnets are crucial for jet fighter engines, missile guidance systems, military gear, and other defense applications where components must maintain magnetic properties under extreme conditions. Additionally, samarium serves critical functions in nuclear reactor control rods, leveraging its high neutron absorption cross-section, and in specialized lasers for defense and industrial applications.

The criticality of samarium is amplified by the extreme concentration of global rare earth element supply. Between 2011 and 2017, China produced approximately 84% of the world’s rare earth elements, while the United States contributed only about 4% during its limited production period from 2012-2015. This supply concentration is particularly acute for samarium because it occurs as a minor component within rare earth deposits – comprising only 0.79% of the rare earth oxide content at Mountain Pass, California, and 0.80% at Bayan Obo, China. The low concentration means that samarium availability is directly tied to the mining and processing of bulk light rare earth elements, making independent samarium production economically unfeasible. When China announced export restrictions in 2010 through quotas, licenses, and taxes, it highlighted the vulnerability of samarium-dependent industries.

The strategic importance of samarium extends beyond current applications to emerging clean energy technologies. Samarium is used in nickel-metal hydride batteries alongside other rare earth elements, with these batteries containing significant quantities of rare earths for hybrid and electric vehicles. As the world transitions to clean energy, demand for samarium in both permanent magnets for wind turbines and electric motors, and in advanced battery systems, is expected to increase. Expert panels from the National Research Council, U.S. Department of Energy, and European Commission have consistently ranked rare earth elements including samarium as having high “criticality” – combining high technological and economic importance with severe supply-side risk.

The supply vulnerability of samarium is compounded by the complexity of rare earth processing and the limited number of facilities capable of separating individual rare earth elements. Most rare earth separation capacity is concentrated in China, meaning that even when rare earth ores are mined elsewhere, they often must be sent to China for processing into individual elements like samarium. With global reserves of rare earth oxides at 130 million metric tons but only a handful of active mines – including Mountain Pass in California, Bayan Obo in China, and Mount Weld in Australia – the supply chain for samarium remains fragile. The combination of samarium’s irreplaceable properties in high-temperature magnets and nuclear applications, its minor occurrence within rare earth deposits, the concentration of both mining and processing in China, and growing demand from defense and clean energy sectors firmly establishes samarium as a critical raw material for advanced economies.

Interesting Facts About Samarium

1. Samarium has the highest thermal neutron absorption cross-section of any stable element (5,922 barns for Sm-149), making it crucial for nuclear reactor control rods and neutron shielding applications.
2. Unlike most rare earth elements, samarium exhibits two oxidation states (+2 and +3) in compounds, with Sm(II) being a powerful reducing agent comparable to metallic sodium.
3. Samarium-cobalt magnets (SmCo5 and Sm2Co17) maintain their magnetic properties up to 700°C, far exceeding the ~300°C limit of neodymium magnets, making them essential for aerospace and military applications.
4. The element displays unusual magnetic behavior, transitioning from paramagnetic to antiferromagnetic at 14.8 K, then to a complex helical magnetic structure at even lower temperatures.
5. Samarium-147 undergoes alpha decay with a half-life of 106 billion years, making it useful for dating extremely old geological samples and meteorites predating the solar system.
6. The metal has seven naturally occurring isotopes, more than most rare earth elements, with isotopic abundances varying significantly in extraterrestrial samples.
7. Samarium exhibits negative thermal expansion below 13 K, meaning it actually expands when cooled rather than contracting like most materials.
8. The element forms unique organometallic compounds with cyclopentadienyl ligands that catalyze polymerization reactions impossible with other rare earth elements.
9. Samarium(II) iodide is one of the most selective single-electron transfer reagents in organic chemistry, enabling reactions that form carbon-carbon bonds under mild conditions.
10. The metal’s vapor pressure is anomalously high among rare earths, subliming at relatively low temperatures (1794°C) compared to its neighbors in the periodic table.
11. Samarium has an unusually complex crystal structure that undergoes multiple phase transitions, including a unique rhombohedral phase not seen in other lanthanides.
12. The element’s spectral lines were used to confirm the theory of isotope shift in atomic spectra, contributing to early understanding of nuclear structure.
13. Samarium-doped crystals exhibit sharp fluorescence peaks that make them ideal for solid-state lasers operating at specific wavelengths around 650 nm.
14. The metal reacts with hydrogen to form both SmH2 and SmH3, with the trihydride displaying metallic conductivity unlike most metal hydrides.
15. Samarium compounds show exceptional catalytic activity for methane conversion, outperforming other rare earth catalysts in direct methane-to-methanol reactions.
16. The element has an unusually large atomic radius jump between its +3 and +2 oxidation states, causing dramatic color changes from pale yellow to blood red.
17. Samarium-153 is used in medicine as a bone cancer treatment, with its beta radiation specifically targeting bone metastases while sparing healthy tissue.
18. The metal forms glasses with unique optical properties when combined with aluminum and oxygen, creating materials transparent in both visible and infrared spectra.
19. Samarium exhibits the strongest magnetostriction among light rare earth elements, changing shape significantly in response to magnetic fields.
20. The element’s discovery in 1879 by Paul-Émile Lecoq de Boisbaudran required processing 150 kg of samarskite ore to isolate just a few grams, demonstrating its extreme scarcity even among rare earths.

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