In ancient times, they were considered magical objects with supernatural powers. These days, we just stick them on our refrigerators. Yet those little magnets deserve our admiration more than ever.
Take laptop computers, with their slim hard drives. It became possible to manufacture the motors for those drives only after the development of especially powerful permanent magnets in the early 1980s. Such muscular magnets are now found in many other places as well—various household appliances, cellphones, and the small electric motors that operate accessories in our cars, to name a few. They are also critical in the brawny electric motors that propel hybrid vehicles and in the generators attached to many wind turbines. So they can help both to reduce energy consumption and produce green electric power.
Because the magnets themselves are hidden away, many of us tend to take them for granted. We shouldn't, especially not now. The manufacture of most high-performance magnets requires neodymium, a rare earth element that's in short supply. Almost all of the world's production comes from China, which has increasingly restricted exports to ensure that it has enough to satisfy its own needs. So the price of neodymium has been skyrocketing. If the trend continues, pretty soon we'll have a real crisis on our hands.
Mining companies are scrambling to develop other sources of neodymium ore, a process that can take a decade or more. But what if you could make magnets even more powerful than today's best using less neodymium, or maybe even using an element that's a lot more plentiful? Not only would that ease concerns about shortages, it would result in smaller and more efficient motors and generators.
In the past, when researchers went looking for ways to make better permanent magnets, they were pretty much restricted to combining various mostly metallic elements into a single magnetic alloy. Now some of us are pushing an entirely different approach: We hope to construct ultrastrong magnets using two different alloys combined at the nanometer scale. That's not an easy thing to do, but if researchers can overcome the remaining technical obstacles, such "nanocomposite magnets" could allay worries over the dwindling supply of neodymium. And such magnets could make motors, generators, loudspeakers, and the like more compact and efficient, which is a worthwhile goal in itself.
How do you go about making a permanent magnet? Magnetism starts with individual atoms, so let's begin there. Only some kinds of atoms are magnetic, having what physicists call a magnetic moment, meaning that the atom acts like a tiny bar magnet. You'll definitely want to enlist atoms that are strongly magnetic in your creation. Iron, nickel, and cobalt all qualify. The rare earth elements neodymium and samarium are even better. The way those atoms are arranged is also important: You'll need a material in which these atomic bar magnets naturally tend to line up. This happens in many crystalline substances because of something physicists call exchange forces, a quantum-mechanical effect that operates over just a few nanometers, coaxing the magnetic moments of nearby atoms to align.
In many materials, that alignment is easily disturbed, destroying the magnetization. To avoid that, it's best to pick a material whose crystal lattice has just one direction that the magnetization can easily align with—think of the grain in a piece of lumber. Physicists call this, naturally enough, the easy direction of magnetization. The atomic bar magnets prefer that orientation to any other, which makes for a stable, or as physicists sometimes call it, a "hard" magnet.
But there's a complication. Most crystalline materials actually consist of many tiny crystallites packed together, so you'll likely be dealing with a bunch of little crystals, each with its own easy direction of magnetization. To get all their magnetic moments working in unison, you have to take pains to orient the easy directions of all the crystallites in parallel. Even if you're successful, the thing you create probably won't be uniformly magnetized. Instead, it will spontaneously divide itself into what are known as magnetic domains. The magnetic moments inside each domain will lie along the easy direction, but left to themselves, adjacent domains will point in opposite directions, canceling each other out.