High-efficiency nano-scale deposited magnetic composites as replacements for rare-earth materials in motor magnets

I.N. Weinberg, L.O. Mair
Weinberg Medical Physics, Inc.,
United States

Keywords: rare-earth magnets nanoprecision


Magnetic components find many uses in diverse industrial and transport applications, including electric motors and generators found in electric and other vehicles and portable MRI devices. For many of these applications, two qualities make a magnetic component desirable: (1) The magnet generates a strong magnetic field, and (2) The magnet retains that magnetic field at high temperatures. While the commonly-used neodymium-iron based magnets maintain large remanence and energy product, their magnetic fields weaken at fairly low operating temperatures. Magnetic effects are the result of nanoscale interactions between microscopic grains of materials. For thousands of years, the grains in magnets were formed through controlled melting and annealing of various magnetic materials into alloys. The strongest magnets have been formed using alloys that incorporate rare earths (e.g., Neodymium), which are materials that are not available in many countries. There are strong scientific, commercial, and national interest driving forces for technical efforts designed to manufacture strong, high operating temperature magnets that do not rely on rare earth materials. In the past several decades, scientists have shown that the local properties of magnets can be improved by depositing thin films one layer at a time. However, there are multiple challenges to scaling up that approach: (1) The deposition is a very slow process; (2) Alignment of the layers, a critical requirement for bulk magnetization, is not controllable when multiple layers are deposited. Some investigators have shown that nano-scale particles or layers composed of different materials can be engineered to have specific and advantageous magnetic properties. However, those investigators have been unable to build bulk magnets from those nanoscale structures. We have developed a method of constructing large-scale (i.e., centimeter-sized) structures that incorporate layers of magnetic materials whose dimensions can be controlled with nanoscale precision. The process combines advances in magnetic materials engineering with competencies in template-guided fabrication processes for generating bulk materials with nano-scale engineered features. Template-guided synthesis is a method of building structures with nano-scale precision by depositing metals electrochemically into a conducting thin film containing nano-sized holes. Typically, template-guided synthesis results in structures limited to thicknesses of tens of microns, which would not be suitable for production of large-scale magnets for industrial use. We are developing a proprietary additive manufacturing process that creates structures with millions of electrically conductive posts per square centimeter. Each of these posts can be millimeters high and microns wide, and multiple layers of posts can be built to achieve centimeter-sized templates. Users can then successively deposit magnetic materials with nanoscale precision on each post. As a result of the dramatically increased area for deposition, it is possible to rapidly create centimeter-scale customized magnetic structures with pre-specified ratios of magnetic materials and arbitrary shapes. These structures are likely to be able to replace rare-earth magnets. An additional benefit is that the new manufacturing process does not require high temperature smelting operations and is therefore more environmentally sound than conventional magnet fabrication methods.