Alnico is a family of permanent magnets made from an alloy of aluminum, nickel, and cobalt, with iron making up the largest share of the mix. The name itself is a shorthand: Al (aluminum), Ni (nickel), Co (cobalt). Developed in the 1930s, alnico magnets were the strongest permanent magnets available for decades and remain widely used today in applications where heat resistance and stable magnetic fields matter most.
What Alnico Is Made Of
Iron is the base metal in every alnico alloy, typically making up 30 to 46 percent of the total weight. Aluminum, nickel, and cobalt are the signature ingredients, but their proportions shift depending on the grade. Alnico 2, for example, contains about 17% aluminum, 17% nickel, and 13% cobalt. Alnico 8 pushes the cobalt content up to around 32% while dropping the iron down to roughly 32%.
Most grades also include smaller amounts of copper (2 to 5%) and titanium (up to about 6% in higher grades). These additions fine-tune the magnetic behavior and mechanical properties of the finished magnet. The result is a hard, brittle metallic alloy with a silvery-gray appearance that can only be shaped by casting or grinding, not by machining with standard tools.
Common Grades and How They Differ
Alnico comes in numbered grades, each with a distinct balance of magnetic strength, resistance to demagnetization, and thermal stability. The most commonly referenced grades are Alnico 2, 5, and 8.
- Alnico 2 has moderate magnetic strength and the lowest cobalt content of the three. It produces a relatively soft, warm magnetic field and is a classic choice for vintage-style applications.
- Alnico 5 is the most versatile and widely used grade. It offers stronger magnetic output than Alnico 2 and works well in electric motors, generators, and sensors.
- Alnico 8 has the highest cobalt content and the greatest resistance to demagnetization. It excels in instruments, gauges, and environments where the magnet faces competing magnetic fields or physical vibration.
Higher cobalt content generally means greater coercivity, which is the magnet’s ability to hold onto its magnetism when exposed to opposing forces. Lower-cobalt grades are easier to magnetize and demagnetize, which can be an advantage or a limitation depending on the application.
How Alnico Magnets Are Made
There are two main manufacturing methods: casting and sintering. Cast alnico magnets are made by pouring molten alloy into a mold. This process produces magnets with stronger magnetic properties and allows for larger, more complex shapes. Cast magnets are also anisotropic, meaning they’re magnetized in a specific direction during production, which concentrates their magnetic strength along one axis.
Sintered alnico magnets are made by pressing fine metal powder into a die and heating it until the particles fuse. The magnetic performance is slightly lower than cast versions, but sintered magnets have better mechanical strength and tighter dimensional tolerances. They’re also more cost-effective for high-volume production of small, simple shapes. If an application needs a tiny magnet with consistent dimensions and decent structural integrity, sintered alnico is the typical choice.
Magnetic Strength Compared to Other Magnets
Alnico magnets produce strong magnetic fields, roughly 3,000 times stronger than Earth’s magnetic field. But they are not the strongest permanent magnets available today. Neodymium magnets (made from neodymium, iron, and boron) surpass alnico in raw pulling force by a wide margin. A small neodymium magnet can outperform an alnico magnet several times its size.
Where alnico holds a clear advantage is temperature tolerance. Neodymium magnets start losing their magnetism above about 80 to 200°C depending on the grade, while alnico magnets can operate continuously at temperatures up to 525 to 550°C. Their Curie temperature, the point where magnetism is lost entirely, sits around 860°C. This makes alnico the go-to choice in high-heat environments where neodymium simply can’t survive.
Alnico also has excellent magnetic stability over time. Once magnetized, an alnico magnet loses very little of its field strength through normal aging, which is why it shows up in precision instruments that need to deliver consistent readings for years.
Where Alnico Magnets Are Used
Alnico’s combination of heat resistance, corrosion resistance, and long-term magnetic stability makes it essential in several industries.
In aerospace, alnico magnets are embedded throughout commercial aircraft. They’re found in fuel level sensors, fuel flow meters, and solenoid valves that control fuel pressure. Hydraulic systems use them in position sensors that track the movement of actuators. In the cockpit, traditional analog gauges for altitude, airspeed, and heading rely on alnico-based meter movements. Radar systems use alnico magnets in magnetrons to generate the stable magnetic fields needed for microwave production. Even tachometers that measure engine RPM depend on small alnico generators.
Industrial applications include electric motors, generators, magnetic separators, and sensors of all kinds. Alnico’s resistance to demagnetization from vibration makes it well-suited for equipment that operates under mechanical stress.
Alnico in Guitar Pickups
One of alnico’s most recognizable uses is in electric guitar pickups, where different grades produce distinctly different tonal characters. The magnet sits inside the pickup and creates the magnetic field that converts string vibrations into an electrical signal. Changing the magnet changes the sound.
Alnico 2 pickups are known for warm, smooth tones with a full low end, enhanced midrange, and a sweet high end. They’re a natural fit for blues, jazz, and classic rock. Alnico 3, which has the lowest magnetic pull of the group, delivers a clear, warm sound with a soft top end, giving it an open, airy quality. Alnico 5 pickups are brighter and more aggressive, with a glassy top end, cutting midrange, and tight bass response. They’re the most versatile option, handling clean and distorted tones equally well. Alnico 8 pickups push output even higher, producing a powerful, aggressive tone favored in modern rock and metal.
These tonal differences aren’t subtle. Swapping from an Alnico 2 to an Alnico 5 pickup in the same guitar can dramatically change its character, which is why pickup selection is one of the most common upgrades guitarists make.
Corrosion and Durability
Alnico has naturally good corrosion resistance in many environments. It holds up well when exposed to motor oil, organic solvents, gasoline, and alcohol. It also tolerates dilute organic acids and hydrogen peroxide without significant degradation. Salt water, strong alkaline solutions, and inorganic acids will cause corrosion over time, but in most everyday conditions, alnico magnets can go uncoated for years without visible deterioration.
Protective coatings like nickel plating, zinc plating, or paint are sometimes applied, though they’re often chosen for appearance rather than necessity. The main physical weakness of alnico is brittleness. Like cast iron, it can crack or chip if dropped on a hard surface. It cannot be drilled or machined with conventional tools and is typically ground to final dimensions using abrasive wheels.
Why Alnico Still Matters
Neodymium magnets dominate applications where compact size and maximum pulling force are priorities, but alnico occupies a niche that no other magnet material fills as well. Its ability to operate in extreme heat, resist corrosion without coatings, and maintain a stable magnetic field over decades keeps it relevant in aerospace, industrial sensing, precision instruments, and musical equipment. It’s also free of rare-earth elements, which makes its supply chain less vulnerable to the geopolitical pressures that affect neodymium production. For any application where thermal stability and long-term consistency outweigh raw magnetic force, alnico remains the standard.