A magnet is defined as a material that produces an invisible field that can attract or repel other magnetic materials. The vast majority of magnets are not made from 100% aluminum. Pure aluminum is fundamentally non-ferromagnetic, meaning it cannot generate a sustained magnetic field strong enough to function as a permanent magnet.
Addressing the Aluminum Misconception
The premise that most magnets contain only aluminum is incorrect because the metal is classified as paramagnetic, not ferromagnetic. Ferromagnetism is the property required for a material to form a permanent magnet, characterized by atomic magnetic moments that remain aligned even after an external magnetic field is removed. Aluminum atoms possess unpaired electrons, which allow them to be very weakly attracted to a magnetic field, a characteristic of paramagnetic materials. This slight attraction is negligible, and pure aluminum cannot sustain a magnetic field once the external force is gone. In contrast, the materials used to create permanent magnets, such as iron, nickel, and cobalt, exhibit the strong, enduring magnetic behavior of ferromagnetism.
The Three Main Categories of Permanent Magnets
The modern market for permanent magnets is dominated by three main material categories, none of which rely primarily on aluminum for their magnetic strength. The most common and inexpensive type are Ferrite magnets, also known as ceramic magnets. They are compounds of iron oxide and either strontium or barium carbonate. These magnets are hard, brittle, and highly resistant to corrosion, making them suitable for low-cost applications like loudspeakers and small motors.
The strongest magnets commercially available are Neodymium magnets, a type of rare-earth magnet composed primarily of Neodymium, Iron, and Boron (NdFeB). Their exceptional strength comes from their tetragonal crystal structure, which provides a high maximum energy product. Standard Neodymium magnets are sensitive to rust and typically have a low maximum operating temperature, often limited to around 80°C, requiring protective coatings like nickel-copper-nickel to prevent degradation.
The second major group of rare-earth magnets is Samarium Cobalt (SmCo), which consists of samarium and cobalt, sometimes with added iron and copper. While less powerful than Neodymium magnets, SmCo offers superior thermal stability, maintaining its magnetic properties at temperatures up to 550°C, and excellent resistance to corrosion. This makes SmCo the preferred choice for specialized, high-temperature applications, such as in aerospace and high-performance motors.
Aluminum’s Role in Specialty Alloys
Aluminum does appear as a significant component in one specialty magnetic material known as Alnico, an acronym derived from Aluminum, Nickel, and Cobalt. This alloy typically includes iron and sometimes copper or titanium, with aluminum content ranging from 8% to 12%. Alnico magnets were the strongest type available before rare-earth magnets were developed in the 1970s. Aluminum does not contribute to the alloy’s ferromagnetism, but its inclusion, along with nickel and cobalt, creates a microcrystalline structure that yields specific magnetic characteristics. Alnico magnets are manufactured through casting or sintering powdered metals together. The resulting alloy is known for its high residual induction and exceptional temperature stability, maintaining performance above 525°C. This thermal resistance keeps Alnico relevant for applications like sensors, guitar pickups, and certain meters.