Magnetism plays a central role in the development of many exciting new technologies including lasers, medical imaging devices, and computers. As such, there is a continued need to further understand and exploit this phenomenon. Now, R. Oszwaldowski and I. Zutic of the University at Buffalo and A. Petukhov of the South Dakota School of Mines and Technology have proposed that, at very small scales, it may be possible to create a quantum dot that is magnetic under surprising circumstances.
As reported in the April 29 issue of Physical Review Letters (DOI: 10.1103/ PhysRevLett.106.177201), the researchers describe a theoretical scenario involving a quantum dot that contains two mobile electrons with opposite spins, along with manganese atoms fixed at precise locations within the quantum dot. The mobile electrons act as “magnetic messengers,” using their own spins to align the spins of nearby manganese atoms.
Under these circumstances, conventional thinking would predict that each electron would exert an equal (but of opposite sign) influence over the spins of the manganese atoms such that neither is able to “win.” However, the researchers show that the quantum dot’s two mobile electrons actually influence the manganese spins to different degrees.
This occurs because while one mobile electron prefers to stay in the middle of the quantum dot, the other prefers to locate further toward its perimeter. As a result, manganese atoms in different parts of the quantum dot receive different messages about which way to align their spins.
In the “tug-of-war” that ensues, the mobile electron that interacts more intensely with the manganese atoms aligns more spins, which causes the entire quantum dot to become magnetic.
This prediction, if proven, could “completely alter the basic notions that we have about magnetic interactions,” Zutic said. Studying how magnetism works on a small scale is particularly important, Zutic said, because “we would like to pack more information into less space.”
