What causes magnetization relaxation in ferromagnetic transition metals? – Snorri Ingvarsson

Date: Wed. March 26th, 2003, 12:30 pm-1:30 pm
Location: Rockefeller 221

Much like resistance is to an electric circuit, magnetization relaxation is what restores the magnetization of a ferromagnet to equilibrium when the external stimulus (magnetic field) becomes quiescent. The mathematical equation governing magnetization dynamics in ferromagnets is the Landau-Lifshitz equation, where magnetization relaxation is usually taken into account as a phenomenological damping constant (Gilbert damping). In designing magnetoelectronic devices such as magnetic random access memory, it is obviously very important to understand what lies behind the Gilbert damping constant, and to understand how it can be modified. But what is this Gilbert damping really? In our experimental studies of magnetic thin films we have found that there is a strong correlation between their electrical resistance and Gilbert damping, indicating that the relationship between the two is much closer than the simple analogy mentioned above. It suggests that the underlying mechanism of Gilbert damping is the interaction between conduction electrons in the magnet and its magnetization. This interpretation has helped provide an understanding of two other sets of results. In one case Gilbert damping in a thin magnetic film was affected dramatically by adjoining it with certain nonmagnetic transition metal layers. In the other case damping was increased by alloying with certain transition metal elements.