Samarium

What Is Samarium

Samarium is element 62 — a light rare earth element in the lanthanide series, sitting between neodymium and europium. Its commercial importance is almost entirely concentrated in a single application: samarium-cobalt (SmCo) permanent magnets, the only commercially proven magnet technology capable of operating reliably above 300°C.

The dominant commercial magnet technology — neodymium-iron-boron (NdFeB) — is stronger per unit volume than SmCo at room temperature. NdFeB is the magnet in EV motors, wind turbine generators, consumer electronics, and industrial robotics. But NdFeB has a hard physical ceiling. Above approximately 300–400°C, NdFeB magnets begin to demagnetize irreversibly. Adding dysprosium or terbium via grain boundary diffusion can push that ceiling somewhat higher. It cannot push it past approximately 200°C under sustained operation.

SmCo magnets retain full magnetic properties above 700°C. This is not a performance advantage that can be closed by improving NdFeB. It is a structural property of the samarium-cobalt crystal lattice. The physics are different. At the operating temperatures of missile guidance systems, radar actuators, and aerospace motor drives, SmCo is not one option among several. It is the option.

The F-35 Lightning II contains approximately 23 kilograms of samarium-cobalt magnets — in actuators, radar systems, and flight control mechanisms. The AMRAAM air-to-air missile guidance system uses SmCo. So do the phased array radar actuators in the Aegis combat system. None of these applications can migrate to NdFeB without fundamental redesign — and even a redesigned system would face the same physics at the same temperatures.

The Supply Picture — Why China Controls Every Gram

Samarium is not scarce in the ground. It is the fourth most abundant rare earth element in the Earth's crust — more abundant than neodymium, far more abundant than dysprosium or terbium. The supply constraint is not geological. It is processing.

China controls approximately 85–90% of global rare earth separation and refining capacity. Samarium, like other rare earths, occurs in mixed ore bodies — primarily bastnäsite, monazite, and ionic clay deposits. The ore must be mined, concentrated, chemically separated into individual elements, and then reduced to metal. Each step requires specialized facilities, chemistry, and process knowledge accumulated over decades. Outside China, the infrastructure to take samarium from ore to commercial-grade metal simply does not exist at scale.

China's April 2025 export licensing regime covers samarium explicitly. Every shipment of samarium — metal, compounds, or alloys — leaving China now requires a government export license. Approvals are discretionary. The regime does not require denial to be effective as leverage; approval uncertainty alone is sufficient to disrupt procurement planning for defense contractors with multi-year program timelines.

The Western response to samarium specifically has been even thinner than its response to neodymium or dysprosium. Projects building US and allied rare earth separation capacity — MP Materials, Energy Fuels, Lynas — are focused on neodymium-praseodymium and, secondarily, dysprosium and terbium. Samarium separation as a distinct commercial output is not a stated target of any major Western rare earth project with a near-term production timeline.

Defense Applications — Where the Physics Mandate SmCo

The defense supply chain's dependence on samarium-cobalt magnets is not a historical artifact that modern engineering has superseded. It is a current operational requirement that physics has not changed.

Missile guidance systems operate in environments that combine high ambient temperature, mechanical vibration, and electromagnetic interference. The guidance actuators — the mechanisms that move control surfaces to steer the missile — must maintain precise magnetic performance across the full thermal envelope of the engagement. A missile traveling at Mach 4 experiences aerodynamic heating that exceeds 300°C at the airframe surface. The guidance electronics must function throughout the flight. SmCo magnets do. NdFeB magnets at those temperatures do not.

Radar systems with electronically scanned arrays use high-torque motors to position antenna elements. In shipborne Aegis radar installations and airborne radar pods, these motors operate in confined spaces with limited thermal management. The motor magnets must maintain torque output at elevated operating temperatures. SmCo is specified.

Aerospace motor drives — in aircraft environmental control systems, hydraulic pump drives, and actuation systems — operate at continuous duty cycles that generate sustained heat. The motors are sized to fit specific airframe envelope constraints. Substituting NdFeB would require either accepting lower performance at operating temperature or redesigning the airframe envelope. Neither is a near-term option for fielded systems.

The F-35 program alone represents the scale of the dependency. With approximately 23 kg of SmCo per airframe, and a production program that has delivered over 1,000 aircraft with hundreds more contracted, the samarium content already embedded in the F-35 fleet and its production pipeline is measured in tonnes. Sustainment — replacement parts, maintenance spares, future production lots — extends that demand indefinitely.

The DFARS Connection — The Same Clock, A Different Material

DFARS 252.225-7052 takes effect January 1, 2027. The provision requires that rare earth elements used in defense magnets — including samarium — be sourced entirely outside China, Russia, Iran, and North Korea. The requirement covers the full supply chain: mined, separated, processed, and melted.

For NdFeB magnets, there is at least a partial supply chain buildout underway. MP Materials is producing neodymium in the United States. Lynas is building separation capacity. The path to DFARS-compliant NdFeB is difficult, expensive, and behind schedule — but it exists as a project.

For SmCo magnets, the equivalent project does not exist. There is no Western samarium separation facility at commercial scale. There is no US samarium metal production. The DFARS clock for SmCo is running on an entirely different — and far less developed — supply chain. A defense contractor building a DFARS-compliant NdFeB magnet is navigating a difficult but active supply chain development effort. A defense contractor trying to build a DFARS-compliant SmCo magnet in January 2027 is navigating a supply chain that does not yet exist.

The GAO's July 2025 assessment of DoD supply chain visibility found “little visibility” into rare earth manufacturing origins and noted that supply chain efforts were “uncoordinated and limited in scope.” CSIS warned in April 2026 that adhering to DFARS requirements “may not be feasible” by the deadline. Both assessments were primarily framed around neodymium. The samarium situation is structurally worse.

Why It Belongs on This List

The ScarceEarth framework asks one question: does this material sit at the physical floor of a system that cannot function without it?

Samarium sits at the physical floor of high-temperature defense applications. The physics of NdFeB magnet performance define a temperature ceiling that engineering cannot raise above approximately 200°C under sustained operation. The physics of SmCo define a ceiling above 700°C. The gap between those two numbers is where samarium lives, and where it cannot be displaced.

Every defense system that operates above the NdFeB ceiling — every missile that gets hot at speed, every radar that runs hot at duty cycle, every aerospace drive that heats under sustained load — requires SmCo. SmCo requires samarium. China controls samarium. China's April 2025 export controls make that control discretionary and active, not merely structural.

The price figure — $9.77/kg domestic China benchmark — understates the strategic value of the material. The price reflects a domestic Chinese market where samarium is a byproduct of light rare earth separation, available in quantity to Chinese magnet manufacturers. For a Western defense contractor attempting to source DFARS-compliant samarium, the market that figure describes does not exist as an accessible supply option. The number on the price card and the strategic reality of samarium supply are almost entirely disconnected.