Sub-nanosecond resolution x-ray magnetic circular dichroism photoemission electronmicroscopy of magnetization processes in a permalloy ring

Abstract

Fast magnetization processes in a microstructured permalloy ring with80 µm o.d. and 30 nm thickness have been observed by photoemission electron microscopyexploiting x-ray magnetic circular dichroism as the magnetic contrast mechanism.As a high speed probe we employed synchrotron radiation pulses at the ESRF(Grenoble) operated in 16-bunch mode, yielding photon pulses of 105 ps FWHM witha period of 176 ns. Fast magnetic field pulses have been generated by means ofcurrent pulses through coplanar waveguides with the magnetic structure beinglithographically prepared on their surface. A stroboscopic pump–probe set-up witha variable time delay between the field pulse and photon pulse allowed us totake snapshots of the dynamic response of the magnetic domain structure. Weobserved coherent magnetization rotation during the leading edge part of the fieldpulse, the formation of a characteristic domain pattern (‘onion state’) in theplateau region of the pulse and the fast formation of a striped domain pattern(incoherent magnetization rotation) during the trailing edge part of the field pulse. Anumerical simulation confirmed essential features of the stroboscopic image series.