Supercomputers Help Researchers Find Two New Kinds Of Magnets (phys.org)

"Predicting magnets is a heck of a job, and their discovery is very rare," said a mechanical engineering professor at Duke University. But after years of work synthesizing various predictions, material scientists "predicted and built two new magnetic materials, atom-by-atom, using high-throughput computational models." An anonymous reader quotes Phys.org: The success marks a new era for the large-scale design of new magnetic materials at unprecedented speed. Although magnets abound in everyday life, they are actually rarities -- only about 5% of known inorganic compounds show even a hint of magnetism. And of those, just a few dozen are useful in real-world applications because of variability in properties such as effective temperature range and magnetic permanence...

In a new study, materials scientists from Duke University provide a shortcut in this process. They show the capability to predict magnetism in new materials through computer models that can screen hundreds of thousands of candidates in short order. And, to prove it works, they've created two magnetic materials that have never been seen before.
"The first alloy is particularly interesting," reports the International Business Times, "because it contains no rare-earth materials, which are both expensive and difficult to acquire." But a Duke mechanical engineering professor points out that "It doesn't really matter if either of these new magnets proves useful in the future. The ability to rapidly predict their existence is a major coup and will be invaluable to materials scientists moving forward."

Comments

Which supercomputer?

[ShanghaiBill]

TFA seems to leave out a lot of important geeky details. Like which supercomputer was used? How many hours of CPU (or maybe GPU?) time was used? Since they were running hundreds of models in parallel, why did they need a supercomputer at all? Wouldn't it have been more cost effective to rent compute servers in the cloud?

Re:Which supercomputer?

[Dr. Spork]

Alnico magnets are awesome as pole pieces in pickups for electric guitars and basses. This year I started winding my own bass pickups, after testing many commercial pickups to get a sense of how the physical parameters affect tone. I can tell you that the kind of magnet you use makes an obvious difference to the sound of the instrument. It's not just about the net strength and geometry of the fields. Alnico magnets - but not ceramic, nor Nd - get eddy currents induced inside them from the vibrating strings, and this affects how they sound. I wonder whether Co2MnTi would also have these. I get the impression it's not a proper homogeneous alloy, so maybe not. Still, more info and a comparison field strengths would be useful. To a musician, a new type of magnet might be something like a newly discovered species of aromatic fruit: You immediately wonder what new aesthetic experiences it would allow for.

Re:Question for the Physicists.

[poodlediagram]

A permanent magnet is polarized by something called the exchange field. This is related to the Pauli exclusion principle and the Coulomb interaction and happens spontaneously. Energy is stored in the electronic state as kinetic, external and interaction (this includes the magnetic dipole field energy)

These two new magnets are unlikely to replace the current champion (neodymium-iron-boron), or be particularly useful as permanent magnets at all. The reason is that the researchers only calculated the moment and Curie temperature. A good permanent magnet should also have a high magnetic anisotropy energy (MAE) as well. The Heusler alloys are predominantly cubic and so have a very low MAE.

How do I know this? We just spent three years doing exactly the same thing: spending thousands of CPU hours trying to find a good magnet among the Heuslers. All to no avail.

Re:Question for the Physicists.

[rgbatduke]

Here is a really cool fact that you can use to impress chicks at cocktail parties: A magnetic force and an electrical force are the SAME THING. The only difference is your inertial frame of reference. Let's say you have two parallel copper wires with current flowing through them. The negative charge in the electrons and the positive charge in the copper nuclei should cancel each other out, and there should be no force between them. BUT THERE IS. This is magnetism. But it is really just plain only electrical attraction because the electrons are moving, so their inertial reference frame is different from the reference frame of the copper nuclei. A moving reference frame has a Lorentz contraction, so the copper nuclei "see" more electrons per length of wire, resulting in an attraction.

No. Magnetic and electrical force and energy aren't exactly "the same thing". The magnetic and electric field are both components of the second rank field strength tensor, the Lorentz force in electromagnetic theory is not just the Lorentz transform of the Coulomb force, and magnetic and electric field energies are independently summed when assembling the total electromagnetic field energy density. Finally, good luck describing electron spin and the resultant intrinsic magnetic dipole moment in terms of a Lorentz transformation of the bare Coulomb field of the (point) charge -- there is no rotating frame or mass moving around mass.

There are basically two different ways to discuss them. One way is to stop talking about electric and magnetic fields independently at all and only work with the electromagnetic field (strength tensor) where the electric and magnetic components are NOT THE SAME and do NOT HAVE THE SAME SYMMETRY. The other way is to pretend (as most intro books do, because usually it works pretty well if you're considering low velocities and coarse-grain-averaged "smooth" charge/current densities) that E and B are ordinary vectors and write down Maxwell's equations. There are FOUR of them -- two if you go with the covariant field strength tensor formulation, and you cannot write them all down in terms of a single vector field (or the resultant force).

F_e = qE (F, E vectors)
F_b = q v x B (F, v, B vectors)

The electrostatic force obeys Newton's third law. The magnetic force (with the cross product) does not,. and one has to work very hard indeed to find the missing energy and momentum in the electromagnetic field when two charged particles interact in the general case.

Sadly, I haven't found that knowing graduate level electrodynamics well enough to teach it impresses chicks at cocktail parties.

Re: Question for the Physicists.

[Immerman]

I was referring, badly, to motors using permanent magnets in the stator or armature, as opposed to those based entirely on electromagnets.

Actually though, you can make temporarily "perpetual motion" magnetic motors that draw power entirely from draining the energy stored in the magnets - for example, picture the situation where magnets on the rim of a wheel are attracted to a stationary magnet nearby. Then, roughly at the point of closest approach, the rim magnets pass behind some form of shielding so that there is no symmetrical force required for them to be moved away again. Unlike gravity (so far as we know) magnetic fields can be blocked, and so the rim magnets will perpetually "fall" towards the stationary one until the magnetic field is drained. You can do something similar with electrostatics as well, and many people have convinced themselves they've managed to create a perpetual motion machine that way.