Physics and Astronomy Calendar

One of the current frontiers in magnetism is to understand the domain structure and the magnetization reversal in nanometer sized particles. Explorations at these length scales have been aided by the development of new magnetic imaging techniques 1 one of which is the magnetic force microscope (MFM), a variant of the atomic force microscope. We have utilized the high resolution MFM (30 nm) we developed 2 to increase our fundamental understanding of magnetism on this length scale. I will discuss the field induced magnetic reversal in stadia shaped particles on the order of hundreds of nanometers wide and about twice that in length. In general for the small aspect ratio stadia (length to width ratio) the magnetization reverses by the formation of a single vortex and its propagation down the length of a stadium (when the fields are applied perpendicular to the long axis). The surprising discovery is the importance of virtual particles (vortex-antivortex pairs) creation and annihilation in the magnetic reversal in larger aspect ratio stadia.

1. E. Dan Dahlberg and Jian-Gian Zhu, Physics Today _48_, 34 April 1995.

2. George D. Skidmore, Sheryl Foss, and E. Dan Dahlberg, Appl. Phys. Lett. _71_, 3293-3295 (1997).

Supported by ONR and the University of Minnesota MRSEC.