Many of the industrial motors used today are induction motors. However, permanent magnet motors are generally more efficient than induction motors and can be more cost-effective in the long run, especially for factories and plants that run constantly. Currently, most permanent magnet motors rely on critical materials, specifically rare-earth based high-performance magnets, which are costly and exceed the performance needs of many industrial applications.

A team of researchers and industry partners led by scientists at the US Department of Energy Ames National Laboratory has developed a rare-earth-free bonded magnet that not only retains its magnetism at high temperatures, but its coercivity nearly doubles with a 100 °C (212 °F) increase from room temperature.

Coercivity is the measure of the magnet’s ability to resist demagnetization when it is exposed to an external magnetic field. High temperatures can cause magnets to lose their coercivity. Industrial motors run at very high temperatures, so a permanent magnet designed for an industrial motor needs to maintain its coercivity at very high temperatures.

The magnet the team developed is a combination of magnesium and bismuth (MnBi). The key to its performance lies in the preparation and fabrication process.

Magnets have tiny crystal-like structures called grains that appear at the microscopic level and can influence magnetic behavior. Jun Cui, a scientist at Ames Lab and the team leader explained that the interaction between these grains can have a negative impact on magnetic performance.

We don’t want those grains to touch each other. If they touch, they will establish some sort of a communication, and it takes only one imperfect grain to convince the whole neighborhood and create an avalanche-loss of magnetism.

—Jun Cui

To prevent grain interactions, Cui’s team developed a process to isolate the grains from each other during the fabrication process. They start by turning the material into an extremely fine powder. Next, they coat each of the particles with a delicate polymer solution that prevents grain-to-grain contact.

During fabrication, the researchers use an external magnetic field to align the particles. This process results in formation of an anisotropic magnet, explained Wei Tang, also a scientist at Ames Lab. Anisotropic magnets have a preferred direction of magnetization, which enhances the magnet’s overall performance.

Cui also pointed out that bismuth, one of the key elements in this new magnet, is not only naturally available but is also a byproduct of smelting and refining other materials. Utilizing the byproduct contributes to cost saving and resource efficiency for this material, making it an economical choice.

Cui and Tang explained that they did have to sacrifice some magnetic force when crafting this magnet to have high coercivity, but this tradeoff aligns with the specific needs of many industrial applications.

If we look at the whole world right now, actually, motors can operate without magnets. But on the other side, high efficiency motors require high-performance magnets. We are developing something in between, and offering a balanced solution: an affordable, non-rare-earth magnet for targeted industrial tasks.

—Jun Cui

The team has already collaborated with an industrial partner to test this magnet in an industrial pump motor. The motor performed slightly better than the design specifications. The industry partners have already moved on to “fatigue tests,” where they assess the performance and endurance of the new magnet motor.