Material
Rare Earth Magnets
Permanent magnets built on neodymium-iron-boron or samarium-cobalt, the strongest magnets made and the enabling component in every electric actuator, motor and precision guidance system. The most concentrated supply chain in this atlas, and the only material here whose entire production history, not just its melt source, is restricted by federal acquisition rule.
Overview
A rare earth magnet holds far more magnetic energy per unit volume than any alternative, which is why a modern actuator, servo, motor or seeker is built around one. NdFeB gives the highest energy product and dominates by volume; SmCo gives up roughly a third of that strength in exchange for working to 350 degrees C and beyond, and for corrosion resistance NdFeB cannot approach. The chain that produces them is long and unusually easy to break: ore is mined, mixed concentrate is separated into individual oxides by hundreds of stages of solvent extraction, oxide is reduced to metal, metal is melted and strip cast to alloy flake, flake is milled to single-crystal powder, and powder is aligned in a magnetic field, pressed, sintered and heat treated. Any one of those steps happening in the wrong country contaminates the finished part for defense purposes. Mining is the step everyone talks about and the least difficult; separation and metal reduction are the genuine chokepoints, and both sat almost entirely outside the United States until very recently.
Supply chain
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Processes performed on material you already own.
Defense applications
Precision guidance and control actuation
Fin and control surface actuators on guided munitions are built around permanent magnet motors, because the power density of a rare earth magnet is what allows an actuator small enough to fit inside a missile body to move a control surface against aerodynamic load. There is no non-magnetic substitute at the same size and weight.
Control actuation systems, Fin actuators, Seeker gimbal drives, Thrust vector actuators
Electric propulsion and drive motors
Permanent magnet motors and generators dominate where power per unit mass matters. Ship electric drive, aircraft electrical generation, directed energy prime power and hybrid ground vehicle drive. A magnet grade change is not a swap: it moves torque, thermal margin and demagnetisation limits at once.
Integrated electric propulsion, Aircraft starter-generators, Hybrid drive traction motors, Auxiliary power units
Sensors, sonar and countermeasures
Magnetrons, travelling wave tubes, sonar transducers and magnetic sensors all depend on stable field strength over temperature and time. This is where samarium-cobalt earns its cost premium: its temperature coefficient is far flatter than NdFeB, so the field does not drift as the equipment heats.
Travelling wave tubes, Magnetrons, Sonar transducers, Magnetic bearings
High temperature and space environments
Above roughly 150 degrees C, ordinary NdFeB begins to lose field irreversibly. Dysprosium or terbium additions push that higher at considerable cost, and beyond about 200 degrees C samarium-cobalt becomes the only practical choice. One grade family is rated for continuous operation to 550 degrees C.
Engine-mounted generators, Downhole and high temperature actuators, Satellite reaction wheels, Radiation-environment sensors
Alloys and grades
| Designation | Grade | Class | Notes | Typical forms |
|---|---|---|---|---|
| NdFeB (Nd2Fe14B) | N-series, e.g. N42, N52, N42SH | Neodymium-iron-boron sintered magnet | The highest energy product permanent magnet in production and the volume default. Grade codes carry two parts: a number for energy product and letters for temperature and coercivity class, so N52 is the strongest and N42SH trades energy product for heat resistance. Temperature capability is bought with dysprosium or terbium. | Sintered Permanent Magnet, Bonded Magnet, Magnet Alloy, Powder |
| SmCo 2:17 (Sm2Co17) | e.g. R26, R32, and high temperature variants | Samarium-cobalt sintered magnet, 2:17 phase | The high temperature workhorse. Lower energy product than NdFeB but a far flatter temperature coefficient and much better corrosion resistance, usually run uncoated. Specialist grades are rated for continuous operation to 550 degrees C. | Sintered Permanent Magnet, Magnet Alloy, Powder |
| SmCo 1:5 (SmCo5) | e.g. R18, R20 | Samarium-cobalt sintered magnet, 1:5 phase | The earlier samarium-cobalt phase, lower energy product than 2:17 but with very high intrinsic coercivity, which suits thin sections and strongly demagnetising circuits. | Sintered Permanent Magnet, Magnet Alloy |
Properties
| Property | Value | Unit | Note |
|---|---|---|---|
| Maximum energy product (sintered NdFeB) | 33 to 52 | MGOe | The headline figure. Higher grades trade coercivity and temperature capability for energy product. |
| Maximum energy product (sintered SmCo) | 16 to 32 | MGOe | Roughly a third to two thirds of NdFeB, bought back in temperature and corrosion performance. |
| Maximum operating temperature (NdFeB) | 80 to 230 | degrees C | Grade dependent, and heavily dependent on dysprosium or terbium content. The low end is ordinary commercial grade. |
| Maximum operating temperature (SmCo) | 300 to 550 | degrees C | The reason SmCo survives commercially at all despite lower energy product. |
| Curie temperature (NdFeB) | 310 to 400 | degrees C | Field is lost entirely above this. Practical operating limits sit far below it. |
| Curie temperature (SmCo) | 700 to 800 | degrees C | |
| Corrosion behaviour (NdFeB) | Poor uncoated | Sintered NdFeB oxidises readily and is essentially always nickel, zinc, epoxy or parylene coated. Coating is part of the part definition, not a finish. | |
| Mechanical behaviour | Hard and brittle | Sintered magnets are ground, not machined, and chip readily. They cannot be tapped, threaded or turned. |
Advantages
- Far higher energy product than any alternative magnet, which is what makes small high-torque actuators and motors possible at all
- Enables power-dense electric propulsion, actuation and generation where mass and volume are constrained
- Samarium-cobalt holds field stability to 350 degrees C and beyond, with a much flatter temperature coefficient than NdFeB
- Bonded grades can be moulded to complex net shape and tight tolerance without grinding
Limitations
- The supply chain is the most concentrated of any material in this atlas, and the concentration is in separation and metal reduction rather than in mining
- Sintered NdFeB corrodes readily and must be coated; the coating is a qualification item, not a finish
- Brittle and non-machinable. Magnets are ground to size, and geometry changes are expensive
- NdFeB loses field irreversibly with temperature, and buying temperature capability means buying dysprosium or terbium, the scarcest and most concentrated elements in the chain
- Handling and shipping are hazardous at size: assembled magnets can crush fingers and erase data, and fine powder is pyrophoric
Governing specifications
| Designation | Body | Scope |
|---|---|---|
| DFARS 252.225-7052 | U.S. Department of Defense | Restriction on the Acquisition of Certain Magnets, Tantalum, and Tungsten. Implements 10 U.S.C. 4872. From 1 January 2027, bars SmCo and NdFeB magnets if any stage of production, mining, refining, separation, melting or fabrication, occurred in China, Russia, Iran or North Korea. |
| 10 U.S.C. 4872 | United States Code | Acquisition of sensitive materials from non-allied foreign nations: prohibition. The statute behind DFARS 252.225-7052; also covers tantalum and tungsten. Formerly numbered 10 U.S.C. 2533c, and older supplier compliance statements still cite that number. |
| MMPA 0100 | Magnetic Materials Producers Association | Standard specifications for permanent magnet materials, including grade designations and magnetic property limits. Widely referenced but confirm the current issuing body and revision before citing it in a purchase specification. |