Stroboscopic Microscopy of Magnetic Dynamics

Abstract

Abstract. The enhanced capabilities of contemporary pulsed light sources have led to the reflourishing, in recent years, of ultrafast imaging of micromagnetic dynamics. Concurrently, interest in the subject has been intensified by other factors, such as the emergence of intrinsic magnetic response times as a potential limitation to the ultimate bandwidth of magnetic data storage and by increasingly powerful computer models of magnetic dynamics which call for experimental comparisons. This review contains a discussion of the experimental details behind ultrafast timeresolved magneto-optic imaging, sandwiched between a brief historical overview and a presentation of some recent results, and accompanied by an outline of some future prospects. Historical OverviewThe ongoing development of ultrafast laser technologies has made stroboscopic imaging of fast dynamics in microscopic structures very convenient. The stroboscopic, or "pump-probe" method as it is traditionally named by the optics community, has been grafted onto many different varieties of microscopy, including electron beam, scanning probe (force and tunneling), and, of course, optical (both conventional and near-field) [1,2,3,4]. Some applications of ultrafast optical microscopy are more fully developed than ultrafast scanning probe microscopies, many of which are still not too far beyond the "proof-of-principle" stage. This is largely because the development time for an ultrafast optical microscope is much shorter than that for combinations of ultrafast lasers with other imaging methods.Magnetic structures in particular have provided a major test bed for developments in ultrafast optical microscopy. The magneto-optic activity of ferromagnetic materials ideally suits them for this kind of experimental analysis. With characteristic relaxation times and oscillation periods ranging into the low picosecond range, and with domain wall widths and spin-wave wavelengths in the nanometer range, spatiotemporal investigation of these materials poses a difficult challenge for any type of microscopy. Ferroelectrics are another class with similar characteristics [5].As is often the case, the territory we explore now and find so fertile turns out to have been well surveyed by our predecessors, using the best tools of

PEEM with high time resolution—imaging of transient processes and novel concepts of chromatic and spherical aberration correction

“…The network of domain walls present in the fine stripe pattern obviously stabilizes this phase, also called blocking pattern. 17 This is in agreement with measurements using time-resolved Kerr microscopy 18,19 that revealed a relaxation time of about 50 ns for permalloy structures of similar dimensions. Time resolution in these measurements was limited by the length of the photon pulses, here about 105 ps (16-bunch mode of the ESRF).…”

Recent Developments in Magnetic Measurements: from Technical Method to Physical Knowledge

“…The light sources commonly used are pulsed lasers, whose pulse width can reach values as low as 0.030 ps. The observation is performed on the sample surface by scanning it with a piezodriven stage, acquiring at each spot the Kerr amplitude and reconstructing the magnetic image at a given field [26].…”

FMR Measurements of Magnetic Nanostructures

“…It also yields direct information about the uniform precession mode of the nanowires which can be related to the average anisotropy magnitude [12][13][14][15]. Several measurement techniques which have been used to characterise magnetization dynamics such as femtosecond spectroscopy [16][17][18], pulse inductive microwave magnetometer [19], FMR force microscopy [20], network analyzer FMR [21,31,32] and high-frequency electrical measurements of magnetodynamics [22]. All these techniques can be used for modern application for example in telecommunications and data storage systems.…”