An alnico magnet is a permanent magnet made from an alloy of aluminum, nickel, and cobalt, with iron making up the balance. The name itself is a shorthand: al (aluminum), ni (nickel), co (cobalt). First developed in the 1930s, alnico magnets dominated industrial and consumer applications for decades before rare-earth magnets entered the market. They remain widely used today in guitars, aerospace systems, and sensors because of their exceptional heat tolerance and corrosion resistance.
What’s Inside an Alnico Magnet
The most common alnico alloys contain 23 to 25% cobalt, 12 to 14% nickel, about 8% aluminum, a few percent copper, and sometimes small additions of niobium or silicon. Iron fills out the rest, typically making up around half the alloy by weight. Some grades also include 5 to 8% titanium, which helps create the crystal alignment that gives certain alnico types their stronger magnetic properties.
There are roughly nine standard grades, labeled Alnico 1 through Alnico 9. The lower-numbered grades (1 through 4) contain less cobalt (up to about 20%) and are isotropic, meaning they can be magnetized in any direction. The higher grades (5 through 9) pack in more cobalt and are anisotropic, meaning they’re magnetized along a single preferred direction. That directional alignment gives them noticeably stronger magnetic output.
How They’re Made
Alnico magnets are manufactured through one of two processes: casting or sintering.
Cast alnico magnets are made by pouring molten metal into a mold, then running the solidified piece through a series of heat treatments. This is the more common method and produces magnets with stronger magnetic properties. The trade-off is a rough, dark gray surface that often needs grinding to achieve a smooth finish, and higher production costs per unit.
Sintered alnico magnets start as a mixture of metal powders pressed into shape, then heated to about 2,300°F in a hydrogen atmosphere. The sintering process is better suited for high-volume production and creates magnets that are physically tougher, less likely to chip or crack. Their magnetic output is slightly lower than cast versions, and they tend to work best in smaller sizes.
Magnetic Strengths and Weaknesses
Alnico magnets produce a strong magnetic field relative to their size, with remanence values (the strength of the field they hold after being magnetized) ranging from about 0.83 to 1.20 tesla depending on the grade. Alnico 5, one of the most popular grades, sits at the higher end of that range. That’s a respectable number, though modern neodymium magnets can reach higher energy densities overall.
Where alnico falls short is coercivity, which measures how well a magnet resists losing its magnetism. Alnico’s coercivity is low compared to rare-earth magnets. In practical terms, this means alnico magnets can be partially or fully demagnetized by external magnetic fields, physical shock, or even improper handling. One simulation showed that removing an alnico magnet from its protective magnetic circuit and then replacing it reduced its magnetic strength to about 40% of its original value. That’s a dramatic loss from a single handling mistake.
To prevent this, alnico magnets are often stored with a “keeper,” a soft iron bar placed across the poles that completes the magnetic circuit and preserves the field. If you own alnico magnets, keeping them paired with a keeper or stored pole-to-pole with another magnet makes a real difference in longevity.
Outstanding Heat Tolerance
The standout advantage of alnico is thermal stability. These magnets maintain their performance at temperatures that would weaken or destroy other magnet types. Alnico can operate reliably at temperatures well above 500°C (around 930°F), while neodymium magnets start losing performance at much lower temperatures and are generally limited to applications below 200°C.
This heat resistance is the main reason alnico still dominates in certain industries. In aircraft, fuel system valves and actuators use alnico magnets because fuel lines generate significant heat. Engine compartments, high-altitude temperature swings, and radar systems all create conditions where a neodymium magnet would degrade but alnico performs consistently. Alnico 8, with the highest resistance to demagnetization in the family, is especially popular in aerospace gauges and navigation sensors where precision can’t drift with temperature changes.
How Alnico Compares to Neodymium
Neodymium magnets are significantly stronger per unit of size. If raw pulling force in a compact package is what you need, neodymium wins. But that strength comes with trade-offs that make alnico the better choice in several scenarios.
- Heat tolerance: Alnico handles high-temperature environments with ease. Neodymium magnets lose strength as temperatures rise and can permanently demagnetize if pushed past their rated limit.
- Corrosion resistance: Alnico has very good to excellent corrosion resistance without any protective coating. Neodymium magnets corrode readily and require a nickel or epoxy coating to survive in most environments.
- Brittleness: Both types are brittle, but sintered alnico offers better mechanical toughness than neodymium, which can shatter on impact.
- Demagnetization risk: Alnico is much easier to demagnetize through handling or external fields. Neodymium holds its magnetism far more stubbornly.
The choice between them comes down to the application. For a small motor in a cordless drill, neodymium makes sense. For a sensor inside a jet engine nacelle, alnico is the clear pick.
Alnico in Guitar Pickups
Perhaps the most familiar use of alnico magnets for most people is inside electric guitar pickups. The magnet sits beneath the strings and creates a magnetic field that converts string vibrations into an electrical signal. Different alnico grades produce noticeably different tonal characteristics, and guitarists choose between them the way a painter chooses brushes.
Alnico 2 produces warm, smooth tones with a pronounced midrange and sweet high end. It’s the classic choice for blues, jazz, and vintage rock, delivering a creamy sustain that rewards lighter playing styles. Alnico 3 is even softer, with a clear, warm low end and gentle treble that suits clean, articulate playing.
Alnico 5 is the workhorse. It balances warmth and brightness, with a tight bass response, cutting midrange, and a glassy top end. Players who need versatility across clean and distorted sounds gravitate toward it. Alnico 4 splits the difference between 2 and 5, offering a more even response across all frequencies.
Alnico 8, with its higher coercivity and output, delivers exceptional midrange punch with a tight low end and smooth treble. It’s less common in pickups but popular among players who want a hotter, more aggressive tone without switching to ceramic magnets.
Industrial and Aerospace Uses
Beyond guitars, alnico magnets power a range of industrial systems where reliability under harsh conditions matters more than compact size. Magnetrons in radar systems rely on alnico to produce the stable magnetic fields needed to control electron beams for microwave generation. Solenoid valves in aircraft fuel systems use them to manage fuel flow and pressure in high-heat environments.
Sensors and gauges in navigation systems use Alnico 8 specifically because its higher resistance to demagnetization ensures readings stay accurate over time. Electric motors in legacy equipment, educational demonstration tools, and certain types of relays and switches also use alnico, often because the application was designed decades ago around alnico’s properties and there’s no compelling reason to redesign it.
Cow magnets are another practical, if less glamorous, application. These smooth alnico cylinders are fed to cattle to attract stray bits of wire and metal in the animal’s stomach, preventing hardware disease. The magnet’s corrosion resistance and stable field make it ideal for sitting in a cow’s digestive system for years.
Handling and Storage Tips
Because of their low coercivity, alnico magnets require more careful handling than most people expect from a permanent magnet. Dropping them, exposing them to strong opposing magnetic fields, or storing them without a keeper can cause meaningful, permanent loss of magnetic strength. That 40% loss from a single removal-and-replacement cycle in testing isn’t a worst case; it’s a realistic scenario for careless handling.
Store alnico magnets with a soft iron keeper bridging the poles. If you don’t have a keeper, store two magnets together with opposite poles touching. Avoid placing them near strong neodymium magnets, which can partially demagnetize them. If an alnico magnet does lose strength, it can be remagnetized with a strong enough external field, something a magnet supplier or machine shop can do for you.