Fully controlled precessional switching of a macrospin in a cross-wire geometry

Ultrafast scanning Kerr microscopy measurements of half-precession-cycle, quasiballistic magnetization switching in a Permalloy™ macrospin are presented. The 20×7 μm2, 15-nm ellipse-shaped element is embedded in a continuous film of thinner Py, which effectively eliminates the remanent state closure domains and strongly increases coherence of dynamic motions in the large element. A perpendicular crossing-wire geometry allows pulse excitations to both the easy and hard axes. Data for well-terminated, ringing-suppressed ballistic switching and poorly-terminated switching with ringing are presented with hard axis pulses as small as 12 Oe and as short as ∼400-ps driving precessional switching. With addition of an easy-axis overlapping pulse, half-select precessional switching into a metastable state is observed; however, large spatial nonuniformities are introduced into the element dynamics, which ultimately defeat the half-select switching process.