March 29, 2011 — Magnets made of just a few metallic atoms could make it possible to build radically smaller storage devices, and enable spintronics devices. Nano-sized magnets have only been seen to work at temperatures close to absolute zero. Kasper Steen Pedersen, a chemistry student at the University of Copenhagen, has demonstrated that molecular magnets using ruthenium and osmium retain their magnetic properties at higher temperatures.
The properties observed are most likely due to the larger spin-orbit coupling and more diffuse electron cloud present in these heavier elements.
Pedersen is studying for a masters degree at the University of Copenhagen. He had been working with magnets based on 3D metal ions from iron. Single-molecule magnets are isolated molecules behaving like real magnets but they do not exhibit a three-dimensional order characteristic of a magnet.
"When you take a look at the periodic table of the elements…ruthenium and osmium are in the same group in the periodic table as iron, so it ought to be possible to create magnets out of these substances as well by using our knowledge about molecular magnets based on iron," says Pedersen.
The chemical synthesis needed to build molecular magnets out of the substances was relatively simple. But the measured properties were surprising. "The chemical properties are the same for these metals as for iron. But the physical properties of the new magnets turned out to be very different from those made of iron. Basically, the magnetism arises from the electron spin but also from the motion of the electron around the nucleus. The latter contribution, which is very large for ruthenium, osmium and other heavy elements, has been largely ignored by the scientific community but we have now shown, experimentally, that is a very pronounced effect," explained Pedersen.
Using the unconventional metals for his magnets enabled Pedersen to raise the critical temperature only by a few Kelvin. However, the intriguing result that electron motion plays a large role for the magnetic properties paves the way for new synthetic approaches to molecular nanomagnets with unprecedented high critical temperatures.
Some of his findings have recently been published in Chemistry – A European Journal (Chem. Eur. J. 2010, 16, 13458-13464). Access the article: http://onlinelibrary.wiley.com/journal/10.1002/(ISSN)1521-3765/issues