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The speed of magnetization reversal is a key feature in magnetic
data storage. The data rate in longitudinal recording is currently
100 MB/s and continues to double every two years. This means that
magnetization reversal takes place in times approaching one nanosecond.
In recent experiments we have shown that magnetization reversal
can be initiated by magnetic field pulses of ps duration in thin
in-plane magnetized Co films. The field pulses are generated by
the electron beam at the Stanford Linear Accelerator, and are most
effective for magnetization reversal if the field is applied perpendicular
to the initial magnetization.
Ultrafast magnetic field pulses as short as 2 picoseconds are able
to reverse the magnetization in thin, in-plane, magnetized cobalt
films, as observed by spin-SEM.
The field pulses are applied in the plane of the film, and their
direction encompasses all angles with the magnetization. At a right
angle to the magnetization, maximum torque is exerted on the spins,
leading to the double-ring structure of reversed magnetization,
Figure 1. In this geometry, a precessional magnetization
reversal can be triggered by fields as small as 184 kA/m. At the
direction where field and original magnetization are parallel or
antiparallel no reversal can be induced. The topography image shows
the impact "crater" produced by the high-intensity, high-energy
electron beam.
References
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