UPTON, N.Y., March 29 (UPI) -- Tomorrow's supermagnets could be made of molecule-sized chunks of materials that normally would never interact, possibly creating magnetic fields strong enough to levitate trains at room temperature, a government scientist says.
Laura Henderson Lewis, a materials scientist at Brookhaven National Laboratory's Department of Applied Science, studies how magnetic materials perform and interact at the micro- and nano-scale, which involve groups of hundreds of atoms or even single molecules. She also teaches at the Materials Science and Engineering Department at the State University of New York in nearby Stony Brook.
Lewis has studied magnetic materials for about two decades. She received her bachelor's degree in physics from the University of California at San Diego, then earned a master's degree in electronic materials from the Massachusetts Institute of Technology. Her doctorate in magnetic materials comes from the University of Texas at Austin. She spoke to United Press International from her offices at BNL in Upton.
Q. There are lots of terms applied to this area, nanomagnetics and so on. What's the term you prefer to use for the technology you're dealing with, and what's a good definition to go along with it?
A. Nanocrystalline magnetic materials. Nanocrystalline materials are special, because the constituent grains are very small. Most matter is made up of regions of material on the order of 1 micron to 100 microns (wide, narrower than a human hair). These regions of material fit together like a puzzle, but within each region the atoms are arranged in an extremely regular way, for millions of atoms. If you can imagine a puzzle being made up of pieces about 50 microns in size, that's a regular microstructure.
However, if we make the puzzle pieces extremely small, on the order of 10 to 100 nanometers (1 micron is 1,000 nanometers), interesting things start happening. Nanocrystalline materials are where the puzzle pieces are perhaps 100 atoms in diameter, and the physical properties are radically different from that in the more conventional microstructure.
Why is that special? Because nature has provided us with the perfect length scale for magnetic materials -- the nanometer. If we can reduce the size of the crystals to the nanometer scale, we're reducing it to the natural length scale of magnetism. That allows us to really start playing around with fundamental properties that we just can't access with materials that have a larger crystal structure.
Q. That's an excellent basis to start with. When we talk about constructing magnetic materials on the nanoscale, the analogy of using building blocks starts to fall apart a little bit, because when you're mixing magnetic crystals at that size, it's not as easy as putting them together in a row. They're going to interact because of their different magnetic orientation and such. What are some of the challenges in trying to engineer magnetic materials at that scale?
A. That's a good question. There are a lot of challenges, but also a lot of motivation for trying to get down to that scale. Nature doesn't like to have all those little pieces, so you have to try and fool nature into providing this nanostructure. It's only accessed by special processing methods; for example, you have to resort to rapid solidification. We take the materials from the liquid state to their solid state (in a fraction of a second), so they just don't have time to get into their favorite equilibrium positions.
Another way to reduce the structural scale is to take the materials and beat 'em up for a week. You put them in a jar with some steel balls and apply the technique called ball milling; that eventually reduces the material to a nanostructure by repeatedly fracturing and rewelding the material. In thin-film processing, which is more appropriate to the magnetic recording industry, they apply (thermal and physical diffusion) techniques to get the material to break up into very small pieces. So we know how to do it. It's not always easy, since you have to manipulate the natural tendencies of (the atoms), get in their way and have them avoid where they'd naturally end up.
The benefit, though, for trying to reduce magnetic materials to the nanoscale is huge. As I said earlier, the natural length scale of magnetism is the nanometer. Well, fine, what does that mean? What that means is that magnetic atoms communicate with each other across the nanoscale; they can only communicate to their nearest neighbors or second-nearest neighbors in many materials. If I could pull away one atom and replace it with another, I can completely change the magnetic properties of that material. This is not possible to do on the micron scale, because you just can't dive in, pull off an atom and replace it. On the nanoscale, we can manipulate it so that the edges of the building blocks can be engineered, and the atoms can be replaced by what we want. If we can do that in a controllable way, we can control and access whatever kind of magnetism we would like.
Q. Let's talk about some of the possible uses of that. People normally hear "magnet" and think of a huge electromagnet in a junkyard hauling chunks of cars around. There are a lot more commonplace activities for magnets that people might not realize.
A. I'm glad you asked this question. It was described to me years ago that magnetism is the orphan child of the material science world and the physics world. Most people see magnets on their refrigerator, or they have a clasp on their purse, and they know their credit cards are magnetic, and that's about as far as I'd expect an average consumer to understand how magnets impact their life. It needs to be stated that any application, any device that has a motor in it has a magnet. Immediately, think of everything in your kitchen that has a motor. Cars can have up to 100 magnets in it, depending on how fancy it is -- motors for power windows, antilock brakes have magnets, in some designs the airbag has a magnetic detonator. Magnets are everywhere, in your cell phone, in your walkman, so there's quite a motivation for engineering better magnets. We can get better consumer products, more efficient products, lighter cars, fewer emissions of greenhouse gases from more efficient operation of devices that utilize magnets.
Q. One of the more high-tech applications some people might recognize would be a magnetic levitation train. Today, you need superconducting materials to get the magnetic fields you want to have a train float. What sort of promise do nanocrystalline magnetic materials hold for being to able to engineer the sort of magnets that would make that sort of transportation a reality?
A. Nanocrystal magnets do have the potential to make that sort of commercial transportation go from a future fiction to a present reality. It's going to take a long time -- you're absolutely right, we need superconducting magnets right now to generate a large enough field to actually levitate a train. If we can understand and engineer the nanostructure of permanent magnets (which don't require an electric field to operate), we can make magnets that are stronger and more efficient than the best permanent magnets available today.
If you take the best permanent magnets today, we've pretty much taken everything we can from that particular material -- those today are composed of neodymium, iron and boron. We call them "neo" magnets; they're very useful, but we've hit a wall in terms of nanoengineering these magnets. To take the next step, if we can't make a material that does what we want from one composition, let's put two compositions together. That's where the new future is for permanent magnets. They're called nanocomposite magnets or exchange-spring magnets. For example, common nanocomposite magnets right now are neo magnets and iron; however their grain size is very small. The building blocks for the magnets that work very well are about 10-20 nanometers. We have to get things down to that size, get everybody arranged so they have the optimal neighbors. When that happens, they interact naturally and we can get the best attributes of both magnets, such that they are better than either one taken individually.
Q. We're talking about a lot of possibilities and there's a lot of research going on. If we envision a development scale that goes from basic understanding to commercial use, where might we fall today on that scale with the science of nanocrystalline magnetic materials?
A. To answer that question, I'm going to have to divide the world of magnetism into different parts. Clearly, the data storage industry has a concept to product timescale on the order of months. They have a lot momentum taking them to where they want to go. For the materials I normally work with, I do basic research, the time lag is much greater because we also have an economic factor. The demand for the magnets we work on is driven by the magnetic recording industry, because the motors that drive the read/write heads in the disk drives contain these advanced magnets. The other economic factor is the supply and demand of the rare elements that go in there. The pace is certainly much slower. The breakthrough idea on nanocomposite magnets happened in 1990, and just now there are some market products for niche applications, but the performance isn't spectacular. Theorists tell us we should be getting four and five times the energy product out of these magnets, and we're just not. We still don't understand how the building blocks communicate. So for the permanent magnet industry, if a really great breakthrough in understanding happens, the lag team between that and implementation might be a year.
