Magnetization manipulation by strong electromagnetic fields from highly relativistic electrons

We have pioneered the fastest technique of magnetic switching, today labeled “ballistic” or “precessional” switching, using the powerful electromagnetic field pulses generated in solids by passing through relativistic bunches of electrons from SLAC linear accelerator.

Ultrashort magnetic field pulses can be generated in solids by letting the relativistic electron bunches pass directly through the material. The 50 GeV electron bunches carrying currents up to 1000 Amperes and are focused to a spot size as small as 1 micrometer. The resulting magnetic field lines are equivalent to those of a straight current carrying wire. The field pulse length can be varied and can be as short as 100fs. The magnetic field pulses generated in solid thin films exhibit amplitudes of up to 20 Tesla at distances larger than about 5 microns from the center of impact where the magnetic patterns generated in the material remain entirely undisturbed by the thermal and collisional effects of the electron beam.

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Principle of the experiment with the SLAC FFTB. The highly relativistic electron bunch generates magnetic field lines in the laboratory frame that are equivalent to the ones from a straight current carrying wire. The magnetic pattern shown in this figure was obtained with a pulse length of 4.4 ps. The pattern was imaged in spin sensitive scanning electron microscopy (Spin-SEM) a long time after the field pulse had been applied. The dark areas indicate the regions where the magnetization has switched to the opposite direction. The sample is a 20 nm thick, epitaxial Co film deposited by magnetron sputtering onto a MgO(110) substrate with appropriate buffer layers.

We have demonstrated that the magnetization can be reversed by the ultrashort magnetic field pulses. Ongoing work addresses dynamics triggered by the 100fs pulses and the effects of its magnetic and electric field.