Stretching Alters Magnetics

The mechanical stretching of a single cobalt complex tethered between two gold electrodes alters the molecule’s magnetic states, changing the processes by which electrons flow through the system (Science 2010, 328, 1370). This strategy, developed by physics professor Daniel C. Ralph and postdoc Joshua J. Parks of Cornell University, and their colleagues, not only gives scientists an ideal tool for investigating subtle details of molecular magnetism but could also provide a way to control molecular spin states for applications such as information storage. The group connected an octahedrally symmetric cobalt complex to two gold electrodes. In its normal state, the complex has a cubic shape. They then stretched the complex, distorting it into a tetragon. When the molecule’s symmetry is broken, formerly degenerate spin states separate into discrete levels, which can be observed in spectral lines. This new level of mechanical control over the spin states allowed the group to study a complex, spin-dependent phenomenon known as the Kondo effect, in which the molecule interacts with neighboring conduction electrons.