From wind turbines to electric vehicle motors, permanent magnets play an essential role in many of today’s energy-producing devices. These magnets maintain their properties even when an inducing field is absent, but there’s a limited supply of the rare earth minerals that traditionally have been used in their construction. The manganese bismuth materials have shown lower energy production near room temperature compared with state-of-the-art neodymium-iron-boron magnets. However, magnets using iron coupled with manganese bismuth showed higher energy production than other magnets under development (Alnico, Co-Sm, BaO-Fe₂O₃, SrO-Fe₂O₃, and some low-grade iron-neodymium-boron). Moreover, in situations where the temperature will be greater than 100 degrees centigrade, a magnet of iron coupled with manganese bismuth shows energy production even greater than the state-of-the-art magnet. This manganese bismuth material holds great promise as a replacement for rare earth minerals. However, ultra-pure manganese bismuth material is needed to achieve high energy production and coupling with iron or soft magnets. Until now, no process has been able to fabricate the high-purity, low-temperature phase of the manganese bismuth material needed for viable mass production.

Pacific Northwest National Laboratory has developed such a process, yielding mass or bulk quantities of high purity (greater than 90%) low-temperature-phase manganese bismuth alloys suitable for the scalable production of permanent magnets. The method combines selected atomic ratios of manganese and bismuth metals in either an arc-melter or induction melter to form a stable composite alloy in the form of either an ingot or pellet. Using two temperature regimes with an oxygen-free or reducing gas environment, heat treatment, and particle size control results in a ferromagnetic material with coercivity values (the ability to maintain magnetic properties) that increase significantly with increasing temperatures.

Once thought impossible, the method has higher productivity and lower cost than traditional melt-spinning processes, and it is compatible with current industrial practices.

APPLICABILITY

This high-purity alloy is an ideal candidate for use in electric devices, as well as other applications with elevated temperatures (above 100 degrees centigrade). Specific areas include the following:

• Energy production with high efficiency (for example, wind turbines)
• Electrical motors for vehicles
• Magnetic materials for military applications
• Magnetic materials for toys
• Special high-temperature applications.