1. A microscopic look at the atomic structure of a cobalt-manganese-titanium mixture (Co2MnTi) that is one of the newly predicted and manufactured magnetic materials. Each color shows the distribution of a different element. The uniformity for each material matches the predictions for a stable three-element material.
2. A microscopic look at the atomic structure of a manganese-platinum-palladium mixture (Mn2PtPd), that is one of the newly predicted and manufactured magnetic materials. Each color shows the distribution of a different element. The uniformity for each material — with the exception the small spots indicating a different phase state — matches the predictions for a stable three-element material.
Magnets built atom-by-atom in first effort of its kind, using high-throughput computational models. 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.
The relative scarcity of these materials can make them expensive or difficult to obtain, leading many to search for new options given how important magnets are in applications ranging from motors to MRI machines. The traditional process involves little more than trial and error, as researchers produce different molecular structures in hopes of finding one with magnetic properties. Many high-performance magnets, however, are singular oddities among physical and chemical trends that defy intuition.
In a new study, materials scientists from Duke University provide a shortcut in this process. They predicted 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 2 magnetic materials that have never been seen before. The group focused on a family of materials called Heusler alloys – materials made with atoms from 3 different elements arranged in 1 of 3 distinct structures. Considering all the possible combinations and arrangements available using 55 elements, the researchers had 236,115 potential prototypes to choose from.
To narrow the list down, the researchers built each prototype atom-by-atom in a computational model. By calculating how the atoms would likely interact and the energy each structure would require, the list dwindled to 35,602 potentially stable compounds. From there, the researchers conducted a more stringent test of stability. Generally speaking, materials stabilize into the arrangement requiring the least amount of energy to maintain. By checking each compound against other atomic arrangements and throwing out those that would be beat out by their competition, the list shrank to 248.
Of those 248, only 22 materials showed a calculated magnetic moment. The final cut dropped any materials with competing alternative structures too close for comfort, leaving a final 14 candidates to bring from theoretical model into the real world. After years of attempting to create 4 of the materials, Sanvito succeeded with 2. Both were, as predicted, magnetic.
The first newly minted magnetic material was made of cobalt, magnesium and titanium (Co2MnTi). By comparing the measured properties of similarly structured magnets, they were able to predict the new magnet’s properties with a high degree of accuracy. Of particular note, they predicted the temperature at which the new material lost its magnetism to be 940K (1232F). In testing, the actual “Curie temperature” turned out to be 938 K (1228F) – an exceptionally high number. This, along with its lack of rare earth elements, makes it potentially useful in many commercial applications.
“Many high-performance permanent magnets contain rare earth elements,” said Oses. “And rare earth materials can be expensive and difficult to acquire, particularly those that can only be found in Africa and China. The search for magnets free of rare-earth materials is critical, especially as the world seems to be shying away from globalization.”
The second material was a mixture of manganese, platinum and palladium (Mn2PtPd), which turned out to be an antiferromagnet, ie its electrons are evenly divided in their alignments. This leads the material to have no internal magnetic moment of its own, but makes its electrons responsive to external magnetic fields. While this property doesn’t have many applications outside of magnetic field sensing, hard drives and Random Access Memory (RAM), these types of magnets are extremely difficult to predict. Nevertheless, the group’s calculations for its various properties remained spot on.
http://pratt.duke.edu/about/news/predicting-magnets
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