Samarium occupies a narrow but strategically critical position in the rare earth supply chain, defined almost entirely by its role in samarium-cobalt (SmCo) permanent magnets. SmCo magnets — available as Sm₂Co₁₇ (second generation) and SmCo₅ (first generation) — deliver energy products and operating temperature ranges unmatched by any other commercial permanent magnet system: stable to ~350°C (versus ~180°C for standard NdFeB), inherently corrosion-resistant, and tolerant of radiation environments. These properties make SmCo the only viable magnet option in aerospace and defense applications including precision-guided munition actuators, satellite attitude control, high-speed aircraft motor drives, submarine propulsion components, and radar/EW systems. The US government's FY2024–2025 potential stockpile acquisitions specifically name samarium-cobalt alloy, confirming its status as a named defense-critical material rather than a passive component of the REE basket.

Global Sm production is estimated at ~10,920 tonnes Sm₂O₃ equivalent in 2024 (derived from the USGS-reported 390,000 t world REE total at a ~2.8% basket share), with China supplying ~69% of mine output and controlling ~90% of separation and refining capacity. Sm's production is constrained by the REE balance problem: it cannot be scaled independently of Ce, La, Nd, and other basket elements that co-occur in fixed ratios in any ore deposit. Sm prices have been stable at $2–4/kg (Sm₂O₃, 99.9%) in 2020–2024 — far below the $1,500–2,000/kg peaks seen during the 2010–2012 REE boom — but the supply chain vulnerability is not about price but about control: SmCo alloy production and the separation of Sm₂O₃ from mixed REE concentrates are overwhelmingly Chinese activities.

China's April 2025 imposition of direct export controls on samarium — explicitly naming it alongside Gd, Tb, Dy, Lu, Sc, and Y — marks the sharpest supply-chain risk event in Sm's recent history. Unlike Nd and Pr, which are targeted indirectly through NdFeB magnet technology controls, Sm was named as a directly controlled substance, subjecting Sm metal, Sm₂O₃ oxide, and SmCo alloy exports to license requirements. The path to supply chain resilience for SmCo magnets requires building non-Chinese Sm separation and alloy manufacturing capacity; short of that, US and allied defense procurement faces chronic single-country dependency for a magnet technology with no viable room-temperature substitute in its highest-performance applications.