Alnico is one of the oldest engineered permanent magnet materials still in everyday industrial use, and for a specific set of design problems it remains the best choice available. It does not have the raw strength of a neodymium magnet, but it holds its output across temperature better than any other standard production magnet, and it contains no rare earth elements. This guide covers the grades Dura Magnetics produces, the magnetic and thermal properties that define them, the design tradeoffs that matter, and where Alnico earns its place in a design.
Alnico is an iron-based alloy named for its three primary additions: aluminum, nickel, and cobalt, with cobalt typically running anywhere from about 5% to 24% by weight, plus minor copper and titanium. That composition gives the material a high residual field and, importantly, excellent stability at elevated temperature.
Alnico is produced two ways, and the method affects both performance and part design. Cast and sintered Alnico differ as follows:
Most Alnico is also anisotropic (oriented): during heat treatment the alloy is cooled in a magnetic field, developing a preferred axis that roughly triples its output along that one direction. The magnet must then be magnetized along that axis. Lower grades such as Alnico 2 are isotropic (unoriented), weaker but magnetizable in any direction.
The number in an Alnico grade is an MMPA designation, not a linear strength rating. It identifies a specific composition and process recipe. Dura produces the full range of cast and sintered grades: Alnico 2, 5, 5-7, 8, and 9.
The table below lists representative properties for the cast grades. Values are stated in CGS units (Gauss, Oersted, MGOe) with Tesla in parentheses, consistent with how magnet datasheets are published.
| Grade | Residual Induction Br | Coercive Force Hc | Max Energy Product (BH)max | Max Operating Temp | Type |
|---|---|---|---|---|---|
| Alnico 2 | 7,200 G (0.72 T) | ~560 Oe | 1.5 to 1.7 MGOe | ~450°C | Isotropic |
| Alnico 5 | 12,500 G (1.25 T) | 600 to 640 Oe | 5.0 to 5.5 MGOe | ~525°C | Anisotropic |
| Alnico 5-7 | 13,000 to 13,500 G (1.30 to 1.35 T) | 700 to 740 Oe | ~7.5 MGOe | ~525°C | Grain-oriented |
| Alnico 8 | 8,000 to 9,000 G (0.80 to 0.90 T) | 1,500 to 1,650 Oe | 5.0 to 6.0 MGOe | ~550°C | Anisotropic, high coercivity |
| Alnico 9 | 10,500 to 11,200 G (1.05 to 1.12 T) | 1,375 to 1,500 Oe | 9.0 to 10.5 MGOe | ~550°C | Grain-oriented, high coercivity |
Curie temperature is roughly 860°C across these grades, since it is set largely by the iron-cobalt base alloy. Sintered versions of the same grade run lower in Br and energy product, typically by 10% to 25%, with coercivity and Curie temperature largely unchanged.
A useful way to read the table: Alnico 5 is the workhorse, the grade behind the classic horseshoe magnet, with high field and modest coercivity. Alnico 5-7 and Alnico 9 are grain-oriented premium grades that push energy product higher and are effectively cast-only. Alnico 8 trades field strength for much higher resistance to demagnetization.
This tradeoff is the single most important thing to understand about designing with Alnico. The material has a high residual induction (Br) but a low coercive force (Hc). In plain terms, it produces a strong field but gives that field up easily when exposed to an opposing field, or even to its own demagnetizing field in an open magnetic circuit.
That is why grade selection so often comes down to Alnico 5 versus Alnico 8:
Strong magnets that easily demagnetize are not useful, and neither are weak magnets that resist demagnetization. The right Alnico grade is the one that keeps a usable field at your operating point.
This is where Alnico has no real competition among standard production magnets. It offers the best temperature characteristics of any common permanent magnet material. Dura rates Alnico for continuous-duty service to 500°C (930°F), and per-grade limits run as high as about 550°C for the higher grades. Its reversible temperature coefficient of induction is roughly −0.02 %/°C, the lowest (best) of any production magnet, meaning its output drifts very little as temperature changes.
For comparison, standard neodymium magnets are far stronger at room temperature but begin to lose output irreversibly near 80°C and have a temperature coefficient several times worse. Samarium cobalt is the other high-temperature option and is stronger than Alnico, but where temperatures climb toward and past Alnico’s range, Alnico is frequently the simplest, most stable answer.
Two practical cautions: cooling below ambient is rarely a problem for Alnico, but each circuit should still be evaluated, and exposure above roughly 1000°F causes permanent metallurgical change that can only be reversed by re-heat-treating.
Two physical realities shape every Alnico design.
Geometry matters more than with other materials. Because coercivity is low, a magnet that is short relative to its pole face sits at a low, vulnerable point on its demagnetization curve and can partially demagnetize itself. The fix is geometric: keep the magnet long in the direction of magnetization. A common rule of thumb is a magnetic length-to-diameter (L/D) ratio of about 4:1 or greater, which is exactly why Alnico is so often seen as long bars, rods, and horseshoes rather than thin discs. Treat the specific ratio as application-dependent.
Alnico is hard and brittle. It cannot be conventionally machined or drilled; features and close tolerances are produced by abrasive grinding (and methods such as EDM), while looser features can be left as-cast. Alnico 8 is more prone to chipping than Alnico 5, which is worth keeping in mind on any grade above 6.
Dura casts and sinters Alnico, holds drawings dating back decades, and can supply parts made to your print or provide design assistance on grade, geometry, and magnetization.
Alnico shows up wherever stability and temperature survival outrank maximum flux density:
There is also a current sourcing angle. Alnico contains no rare earth elements, so it sits outside the rare-earth export controls that have disrupted neodymium and samarium cobalt supply. That is a genuine advantage, with one caveat: Alnico’s cobalt content ties it to its own concentrated and currently volatile supply market. Alnico de-risks rare-earth exposure; it does not eliminate critical-mineral exposure entirely.
The right Alnico grade depends on your field requirement, your operating temperature, the space and geometry you have, and your circuit. Getting that combination right is exactly the kind of problem Dura Magnetics solves. Dura designs, casts, sinters, and finishes custom Alnico magnets in-house, and supplies them DFARS, RoHS, and REACH compliant for aerospace and defense programs.
Contact a magnet specialist or request a quote to talk through grade selection and the design of your next Alnico magnet or magnetic assembly.
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