Good Magnets Are “The Rabble”
Today, the reason why mobile phones, earphones and other devices can be made so compact is inseparable from high-performance permanent magnets, which are materials commonly known as “magnets”. So how are these “magnets” made? Can we find stronger “magnets”?
How are “magnets” made?
“Magnet” is scientifically called a permanent magnet, so it is different from an electromagnet that is magnetic when it is electrified. It is the core of many modern technologies. Speakers in small devices such as mobile phones and headphones need permanent magnets to convert current signals into sound signals. Because of super strong permanent magnets, they can only be made so small now. In addition, electric vehicles, turbines, computers, satellites, etc., all need permanent magnets to convert electrical energy and mechanical energy into each other.
So how are permanent magnets made?
It is not difficult to make a permanent magnet. Middle school electromagnetism tells us that the movement of charges produces a magnetic field, and the magnetic field can make charges move. It is for this reason that permanent magnets such as iron cores play a central role in electric motors, generators and transformers. There, they either store energy or convert mechanical and electrical energy into one another. These devices still play a huge role in our lives today.
But explaining how a material like iron acquires and retains a magnetic field requires a little knowledge of modern physics. It all has to do with the behavior of electrons in solid atoms. We know that electrons have spin, and electrons themselves are charged, and the movement of charges generates a magnetic field, so it is like a small magnetic needle. The orientation of the magnetic needle depends on the orientation of the electron spin. In the atoms of most elements, because the spin orientation of the outermost electrons (that is, those electrons that determine the chemical properties of the element) tends to cancel each other exactly, the atoms of the elements are not magnetic. But like iron and its neighboring elements on the periodic table, such as cobalt and nickel, their atoms are only stable when the outermost electrons spin in the same direction, which determines that they always tend to spin in the same direction. One direction, so each atom of these elements is like a small magnetic needle.
But despite this, even if a large number of atoms of these elements gather together, the “magnetic needles” are arranged in a haphazard manner, and the magnetism cancels out, the whole material still does not show magnetism. Only by applying an external magnetic field can the orientation of these “magnetic needles” be adjusted to the same direction. After the external magnetic field is withdrawn, the material still retains the magnetic field. In this way, you have a permanent magnet.
Rare earth permanent magnet materials debut
It is so simple to make a permanent magnet, but it is not easy to make a good permanent magnet. There are many materials used to make permanent magnets, and we can write a long list. Ferrite is used the most because it is relatively cheap and has unrivaled corrosion resistance. But it has a fatal flaw: the magnetism is not strong enough. To generate a strong magnetic field, you need a surprising amount of ferrite. As a result, devices containing ferrite magnets are generally bulky and bulky.
All of this is certainly not a problem for large mechanical devices, but in this era of microelectronics, we need smaller things, which requires permanent magnet materials with stronger magnetic properties. But how? In a solid material, the number of electrons is too large and too complex for theoretical calculations, so it is difficult for theorists to give instructive advice. In this case, the search for better permanent-magnet materials has largely depended on metallurgists fumbling around: mix promising elements, put them under an external magnetic field, and see what happens.
Don’t underestimate this “earth method”, it works again and again. Using this method, the magnetism of the AlCoNi magnets developed in the 1930s was almost double that of the best ferrite magnets. But in this field, a series of breakthroughs occurred after the 1970s, because people discovered an excellent material for making permanent magnets-rare earth metals.
Rare earth elements are also known as “lanthanide elements” on the periodic table of elements, with atomic numbers ranging from 57 to 71. Important rare earth elements include: atomic number 60 rubidium (Nd), 62 samarium (Sm) and 66 dysprosium (Dy). These elements have a characteristic that there are very many electrons in their atoms that can align their spins in the same direction. In the 1970s, people mixed cobalt and samarium in a certain proportion to make permanent magnet materials, and found that its magnetism was twice that of AlCoNi permanent magnets.
The brightest star among permanent magnets
However, an unparalleled dazzling star in the permanent magnet material is the NdFeB permanent magnet (Neo permanent magnet) developed from the rare earth element neodymium plus iron and boron. In the 1990s, a piece of this permanent magnet the size of a fingertip was thousands of times stronger than the magnetic field generated by the Earth’s liquid iron core at equal distances. It should be known that the average distance between the earth’s surface and the liquid iron core that generates the magnetic field of the earth is 2900 kilometers, that is to say, at a distance of 2900 kilometers away from the Neo permanent magnet, the magnetism of the Neo permanent magnet is thousands of times stronger than the earth’s magnetic field .
At room temperature, Neo magnets are the strongest permanent magnets ever created.
But that’s only at room temperature. The early Neo permanent magnets have an annoying defect: they are very sensitive to temperature. When the temperature rises, the magnetism will drop significantly, and it will be completely demagnetized above 100 degrees Celsius. But now people have found an improvement – adding a small amount of dysprosium, another rare earth metal, to the material, which is less sensitive to temperature changes.
At the same time, a technological revolution driven by permanent magnets kicked off. Neo permanent magnets are the first choice wherever you want to generate the strongest magnetic field with the least amount of material: in the engines of cars, in the spindle electric motors in CD and DVD read heads, in headphones and speakers to convert electrical signals The vibrating film that forms the sound, and the super-strong magnetic field required in medical magnetic resonance technology… As of 2010, in terms of transaction volume in the market, although cheaper ferrite still dominates, if the transaction value is based on Calculated, the turnover of Neo permanent magnets is more than ten times or even hundreds of times that of ferrite.
But then came trouble. When the Neo permanent magnet was developed, the demand for rare earth metals soared. Rare earth metals aren’t actually rare on Earth — they’re found in parts per million in the Earth’s crust — and they’re “rare” because rare earth deposits are hard to find. Over the past 10 years, almost all of the world’s supply of rare earths has come from China. However, when the global demand is soaring, in order to give priority to meeting the needs of the country, my country began to adopt a control policy on the export of rare earths in 2012. This caused panic in foreign electronics and microelectronics industries.
Search for new permanent magnet materials
Only 50 grams of Neo permanent magnets are required per computer. This may not seem like much, but considering the number of computers in the world, it adds up to an almost astronomical figure. Nowadays, with the rise of green energy technology, the consumption of computers has been reduced to nothing. Turbine motors in wind farms, as well as electric cars and e-bikes, require lightweight and powerful permanent magnets, and for now, only Neo magnets fit the bill. Each electric vehicle needs to consume 2 kg of Neo permanent magnets. A wind turbine with a power of megawatts needs to consume 2/3 tons of Neo permanent magnets. It is estimated that from 2010 to 2015, the demand for Neo magnets for a single wind turbine will increase by as much as 7 times. Therefore, it is imminent to develop new and stronger permanent magnet materials. It is best to reduce the amount of rare earth metals, and the most ideal situation is to no longer use rare earth metals.
The United States has begun to invest huge sums of money to find new permanent magnet materials. Scientists are currently trying to improve the performance of iron-nickel alloy permanent magnets. Normally, when two magnetic metals, iron and nickel, are fused together, they form a disordered structure in which it is difficult for us to align the electrons in the same direction. But there is one exception, that is, in a kind of ore called tetragonalite, iron and nickel atoms are regularly arranged layer by layer. Once a magnetic field is applied, the electron spins tend to face the same direction.
But this mineral is very difficult to form under natural conditions, especially on Earth. In fact, the only known sample of tetragoolite in the world today comes from a meteorite, and it took at least billions of years to form it. A billion years is certainly too long for us. Scientists aim to synthesize it in the lab, doing what nature has taken billions of years to do.
Another ongoing attempt that seems to be completely “diametrically opposed” is to use carbon as a permanent magnet material. As we all know, graphite and diamond are not magnetic, and doping carbon in pure iron will also make it lose its magnetism. But making compounds of carbon and some other elements into nanoparticles is a different story. Scientists have discovered that this material actually exhibits strong magnetism. Due to commercial confidentiality, scientists are still inconvenient to disclose what this material is and how it is made. But they say the permanent magnet material will one day beat Neo’s permanent magnets in both performance and price.
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