AlNiCo Rod Magnets

Ι What Are AlNiCo Rod Magnets?

AlNiCo, short for Aluminum–Nickel–Cobalt, is a non–rare earth metallic permanent magnet material mainly composed of Aluminum (Al), Nickel (Ni), Cobalt (Co), and Iron (Fe), with small additions of elements such as Titanium (Ti), Niobium (Nb), and Copper (Cu) to fine-tune coercivity. Before rare earth permanent magnets were developed, AlNiCo magnets played a leading role in the permanent magnet industry.

AlNiCo rod magnets are a form of AlNiCo magnet with a long, cylindrical shape, similar to disc magnets but with a much more elongated, narrow profile. They are usually specified by length, diameter, and sometimes magnetic grade, with the length typically much greater than the diameter. Almost all AlNiCo rod magnets are produced by casting, mainly for economic reasons. They are widely used in sensor designs and musical instruments, where stable magnetic performance and consistent geometry are important.

AlNiCo magnets have high remanence but relatively low coercivity. Because their coercivity is low and their recoil permeability (μ_rec) is comparatively large, they are more prone to demagnetization. To reduce this risk, AlNiCo magnets are usually used in a closed magnetic circuit or designed with a high length-to-diameter (L/D) ratio.

For axially magnetized cylindrical magnets, the permeance coefficient (Pc) is calculated using the equivalent magnetic charge method, where L, L_e, and r represent the magnet length, effective length, and radius. When μrec is close to 1, L_e can be approximated as L, which is valid for ferrite and rare earth magnets.

In contrast, each AlNiCo grade has its own μ_rec value, significantly greater than 1. This leads to different effective length factors (k), making L_e much smaller than L and resulting in a lower Pc. In other words, a given physical aspect ratio provides less working stability for AlNiCo than for ferrite or rare earth magnets. For this reason, AlNiCo magnets—especially rods—are typically made longer to achieve a higher Pc and reduce the risk of demagnetization.