Discovered in 1879 by French chemist Paul-Émile Lecoq de Boisbaudran, samarium was named after the mineral samarskite from which it was isolated.

Samarium occurs in concentration up to 2.8% in several minerals including cerite, gadolinite, samarskite, monazite and bastnäsite, the last two being the most common commercial sources of the element.

Samarium is calculated to have one of the largest atomic radii of the elements; with a radius of 238 pm, only potassium, praseodymium, barium, rubidium and caesium are larger.

Upon heating to 731 °C (1,348 °F), its crystal symmetry changes to hexagonal close-packed (hcp),; it has actual transition temperature depending on metal purity.

Thin films of samarium obtained by vapor deposition may contain the hcp or dhcp phases in ambient conditions.

The metal transforms to an antiferromagnetic state upon cooling to 14.8 K.[16][17] Individual samarium atoms can be isolated by encapsulating them into fullerene molecules.

[11][13] Even when stored under mineral oil, samarium gradually oxidizes and develops a grayish-yellow powder of the oxide-hydroxide mixture at the surface.

This effect results in a spectacular color change in SmS from black to golden yellow when its crystals of films are scratched or polished.

[39] The diiodide can also be prepared by heating SmI3, or by reacting the metal with 1,2-diiodoethane in anhydrous tetrahydrofuran at room temperature:[51] In addition to dihalides, the reduction also produces many non-stoichiometric samarium halides with a well-defined crystal structure, such as Sm3F7, Sm14F33, Sm27F64,[38] Sm11Br24, Sm5Br11 and Sm6Br13.

[34] Samarium diboride is too volatile to be produced with these methods and requires high pressure (about 65 kbar) and low temperatures between 1140 and 1240 °C to stabilize its growth.

[56] The cooling-induced metal-insulator transition in SmB6 is accompanied by a sharp increase in the thermal conductivity, peaking at about 15 K. The reason for this increase is that electrons themselves do not contribute to the thermal conductivity at low temperatures, which is dominated by phonons, but the decrease in electron concentration reduces the rate of electron-phonon scattering.

[60] The (C5H5)− ion in samarium cyclopentadienides can be replaced by the indenide (C9H7)− or cyclooctatetraenide (C8H8)2− ring, resulting in Sm(C9H7)3 or KSm(η(8)−C8H8)2.

[60][61] A metathesis reaction in tetrahydrofuran or ether gives alkyls and aryls of samarium:[60] Here R is a hydrocarbon group and Me = methyl.

The chelation prevents accumulation of radioactive samarium in the body that would result in excessive irradiation and generation of new cancer cells.

[75][76][77] Detection of samarium and related elements was announced by several scientists in the second half of the 19th century; however, most sources give priority to French chemist Paul-Émile Lecoq de Boisbaudran.

[78][79] Boisbaudran isolated samarium oxide and/or hydroxide in Paris in 1879 from the mineral samarskite ((Y,Ce,U,Fe)3(Nb,Ta,Ti)5O16) and identified a new element in it via sharp optical absorption lines.

The pure samarium(III) oxide was produced only in 1901 by Eugène-Anatole Demarçay,[84][85][86] and in 1903 Wilhelm Muthmann isolated the element.

Samarsky-Bykhovets, as the Chief of Staff of the Russian Corps of Mining Engineers, had granted access for two German mineralogists, the brothers Gustav and Heinrich Rose, to study the mineral samples from the Urals.

[84][90] The word samaria is sometimes used to mean samarium(III) oxide, by analogy with yttria, zirconia, alumina, ceria, holmia, etc.

Not all rare-earth producers who process bastnäsite do so on a large enough scale to continue by separating the components of SEG, which typically makes up only 1–2% of the original ore.

As of 2012[update], being in oversupply, samarium oxide is cheaper on a commercial scale than its relative abundance in the ore might suggest.

Samarium catalysts help the decomposition of plastics, dechlorination of pollutants such as polychlorinated biphenyls (PCB), as well as dehydration and dehydrogenation of ethanol.

[103] Samarium(II) iodide is a very common reducing and coupling agent in organic synthesis, for example in desulfonylation reactions; annulation; Danishefsky, Kuwajima, Mukaiyama and Holton Taxol total syntheses; strychnine total synthesis; Barbier reaction and other reductions with samarium(II) iodide.

[104] In its usual oxidized form, samarium is added to ceramics and glasses where it increases absorption of infrared light.

Its advantage compared to competing materials, such as boron and cadmium, is stability of absorption – most of the fusion products of 149Sm are other isotopes of samarium that are also good neutron absorbers.

It gave 50-picosecond pulses at 7.3 and 6.8 nm suitable for uses in holography, high-resolution microscopy of biological specimens, deflectometry, interferometry, and radiography of dense plasmas related to confinement fusion and astrophysics.

Saturated operation meant that the maximum possible power was extracted from the lasing medium, resulting in the high peak energy of 0.3 mJ.

The active medium was samarium plasma produced by irradiating samarium-coated glass with a pulsed infrared Nd-glass laser (wavelength ~1.05 μm).

[109] The co-precipitation leads to nanocrystallites of the order of 100–200 nm in size and their sensitivity as X-ray storage phosphors is increased a remarkable ~500,000 times because of the specific arrangements and density of defect centers in comparison with microcrystalline samples prepared by sintering at high temperature.

The latter wavelength is ideal for efficient excitation by blue-violet laser diodes as the transition is electric dipole allowed and thus relatively intense (400 L/(mol⋅cm)).