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We investigated the reversal characteristics of magnetic vortex cores in a two dimensional assembly of magnetic vortices. The vortex lattice was created by film deposition of 30-nm-thick permalloy onto large arrays of self-assembled spherical SiO2-particles with a diameter of 330 nm. The vortex core reversal was investigated by employing a write/read tester. This device uses a state-of-the-art magnetic recording head of a hard disc drive, which allows imaging as well as applying a local magnetic field pulse to individual vortices. The successful writing and reading of individual vortex cores is demonstrated, including a switching map, which indicates the switching behavior dependent on the relative position of the field pulse with respect to the vortex core. [ABSTRACT FROM AUTHOR]

We demonstrate a combined frequency and time domain investigation of injection-locked, constriction-based spin Hall nano-oscillators by Brillouin light scattering (BLS) and the time-resolved magneto-optical Kerr effect (TR-MOKE). This was achieved by applying an ac current in the GHz regime in addition to the dc current which drives auto-oscillations in the constriction. In the frequency domain, we analyze the width of the locking range, the increase in intensity, and the reduction in the linewidth as a function of the applied direct current. Then, we show that the injection locking of the auto-oscillation allows for its investigation by TR-MOKE measurements, a stroboscopic technique that relies on a phase stable excitation, in this case given by the synchronisation to the microwave current. Field sweeps at different dc currents clearly demonstrate the impact of the spin current on the Kerr amplitude. Two-dimensional TR-MOKE and BLS maps show a strong localization of the auto-oscillation within the constriction, independent of the external locking. [ABSTRACT FROM AUTHOR]