Theory of Magnetism and Quantum Tunneling

Prof. Leon Gunther Theoretical work in magnetism focuses on the dynamic behavior of the magnetization which results from thermal activation and from the process of quantum tunneling. This research has a bearing on future developments in information storage using magnetic memory elements (such as the small magnetic particles used in magnetic tapes). Specifically, it addresses the issue of the finite lifetime of the magnetic state that carries the bit of information to be stored.

The most recent exciting development in the area of sample preparation has been the chemically controlled "design" of so-called "spin clusters". A cluster consists of a number of magnetic ions that are strongly exchange-coupled, so that the cluster acts as one large spin. In the future, a spin cluster may well be used to store a bit of information in a computer. Recent work focused on the probability that a spin cluster will tunnel in the presence of a swept applied magnetic field. This process is akin to Zener tunneling. My result has recently been used to determine the tunneling matrix element in the spin cluster "Mn12-Acetate" by repeatedly sweeping the field across zero field and measuring the change in the sample's magnetic moment. Recently, I co-authored a review article on Mn12-Acetate that appeared in the March, 1999 issue of Physics World. Other areas of interest are persistent currents in mesoscopic rings and quantum tunneling in superconducting wires.

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