The "super magnets" are facing competition: An unusual bond between rare earths makes a newly created molecule three times more magnetic than the strongest magnetic substance known to date. A research group led by Colin A. Gould from the University of California at Berkeley constructed a class of substances with two atoms of a rare earth element such as dysprosium or terbium, between which three iodine atoms are arranged in a triangle. As the team reports in Science, the two metal atoms are also connected via a direct bond that runs right through the center of the iodine triangle. According to the team, this bond is not only responsible for the extremely strong magnetism, but also the first direct bond between two rare earths in a molecule.
A substance is particularly strongly magnetic if, on the one hand, it contains many unpaired electrons whose magnetic moment is not directly neutralized by an oppositely oriented partner electron – and, on the other hand, these electrons are all aligned in the same way. Rare earths give off very good magnets, for example the very strong neodymium supermagnets, because they contain many unpaired electrons, which are aligned together by binding to a metal such as iron.
Theoretically, much stronger magnets are possible if you simply use another rare element as a binding partner instead of iron. But so far there has been no fabric with rare earths directly bound. There is such a bond in the new molecule - but it is so weak that the two metal atoms of three iodine atoms have to be held together so that it can form. In this bond there is also an unpaired electron exactly in the middle between the rare earths.
This aligns all other unpaired electrons of both metal atoms equally, so that the entire molecule becomes extremely magnetic. The working group measured the strength of molecular magnetism on the basis of the so-called coercive field strength, among other things. This indicates how strong an external magnetic field must be in order to overcome the internal magnetism of a substance. With two terbium atoms in the molecule and at a temperature of about 60 Kelvin, the coercive field strength was over 25 Tesla, according to the team.
This is not only more than three times the previous record of 7.9 Tesla, but also almost twice the maximum possible field strength in common measuring devices, so that the team has not been able to name an exact value so far. On the one hand, such super-strong molecular magnets are interesting for storage media based on magnetizable substances. On the other hand, according to the team, it is also conceivable to assemble large magnets from these molecules for other technical applications. Their magnetic field strength would once again significantly exceed today's "supermagnets" based on neodymium-containing alloys.
