The history of AlNiCo magnets marks a significant milestone in the development of permanent magnet technology. Before the discovery of Samarium Cobalt magnets in the 1970s, AlNiCo magnets were the strongest permanent magnets available and were the first to be used in large quantities in electromechanical devices.
The first AlNiCo magnet was developed by Japanese metallurgist Tokushichi Mishima in 1932. His-first magnets were cast, isotropic alloys which composed of 25at% Nickel (Ni), 10at% Aluminum (Al) with the balance Iron (Fe). These alloys reached an energy product of about 1 MGOe and a coercive force of about 400 Oe (32 kA/m), which was almost twice that of the best steel magnets available at the time.
These magnets were greatly improved by introducing Cobalt (Co) to substitute part of the Iron. In addition, minor alloying element Copper (Cu), Titanium (Ti), and Niobium (Nb) is added to increase coercivity. Therefore, AlNiCo magnets with energy product between 1.5 and 1.8 MGOe (12.0 and 14.3 kJ/m3) were being produced on a commercial basis by the end of the 1930s.
In 1938, a significant advancement in these materials occurred when it was found that anisotropic AlNiCo magnets could be produced via annealing the alloys in a magnetic field. This finding contributed to the development of permanent magnets with energy products that were up to 5 MGOe (40kJ/m3). These anisotropic magnets eventually became known as AlNiCo 5 through 9 grades of magnets.
Further enhancement to these anisotropic magnets was made by directional cooling of the cast alloys before annealing in a magnetic field. The following research eventually made AlNiCo magnets with energy products as high as 13 MGOe (103.5 kJ/m3).
The history of AlNiCo magnets highlights their role in expanding the use of permanent magnets beyond limited applications like compasses. AlNiCo magnets replaced electromagnets in devices such as loudspeakers, motors, microphones, and sensors, marking the start of widespread adoption of permanent magnets in various industries.
