AlNiCo Rod Magnets

Ι What Are AlNiCo Rod Magnets?

AlNiCo, short for Aluminum-Nickel-Cobalt, is a non-rare earth metallic permanent magnetic material primarily composed of Aluminum (Al), Nickel (Ni), Cobalt (Co), Iron (Fe), and small amounts of other elements such as Titanium (Ti), Niobium (Nb), and Copper (Cu), which help adjust its coercivity. AlNiCo magnets were once the dominant force in the permanent magnet industry until the emergence of rare earth permanent magnets.

AlNiCo rod magnets are a type of AlNiCo magnet with a cylindrical, elongated shape, similar to disc magnets but with a longer, narrower design. They are typically measured by their length, diameter, and sometimes their magnetic strength, with the length usually being significantly greater than the diameter.

Nearly all AlNiCo rod magnets are manufactured through the casting process, primarily due to cost factors. These magnets are commonly used in sensor applications and musical instruments.

AlNiCo magnets are known for their high remanence but low coercivity. Due to their low coercivity and larger recoil permeability (μ_rec), they are more susceptible to demagnetization. To mitigate this, AlNiCo magnets must be used in a closed magnetic circuit or with a high length/diameter ratio (L/D).

The permeance coefficient (Pc) of axially magnetized cylindrical magnets is determined using the equivalent magnetic charge method, where L, L_e, and r represent the length, effective length, and radius of the magnet, respectively. When μ_rec equals 1, L_e can be approximated as L. For ferrite and rare earth magnets, μ_rec is close to 1.

However, each grade of AlNiCo magnets has its own μ_rec value, which is significantly higher than 1. This results in different effective length factors (k), causing L_e to be much smaller than L and consequently leading to lower Pc values. This is why AlNiCo magnets are typically long in length.