Ultrafast magnetization imaging

The magnetodynamics in low-dimensional ferromagnets has become a major challenge in fundamental physics. The question of interest involves how ferromagnetic systems dissipate excess energy when driven by external magnetic switching field pulse. The dominating dissipation mechanisms seem to be, for example, the formation of dynamic domains, magnetization precession, or spin wave propagation, but there is no elucidating general description on this fundamental magnetic process. From the technological point of view, detailed understanding of the magnetization dynamics in mesoscopic magnetic elements is essential to the continued development of high-performance magnetic information technologies. The investigation of such small magnetic structures relies increasingly on magnetic imaging techniques, since the relevant properties vary over length scales from micrometers to nanometers. This paper is intended to provide a detailed description of an experimental method for imaging nonequilibrium magnetic phenomena in the picosecond temporal regime and with submicrometer spatial resolution. The method employs a stroboscopic scanning Kerr microscope, and is capable of measuring simultaneously all three components of the magnetization vector. This experimental approach allows direct insight into the spatiotemporal evolution of magnetization dynamic processes. A few experimental examples will be given, including micromagnetic processes during magnetization switching in small magnetic elements and characterizations of perpendicular magnetic recording heads and a prototype magnetoresistive random-access memory (MRAM) device element.