Magnetization dynamics modeled in magnetic thin films. .One of the challenges facing designers of high data rate computer hard drives and magnetic memory chips is that for most magnetic metals, it typically takes a few nanoseconds for the magnetization to come to rest after it has been switched or "bumped" by a magnetic field pulse. In hard drives, for example, the damping damping In physics, the restraint of vibratory motion, such as mechanical oscillations, noise, and alternating electric currents, by dissipating energy. Unless a child keeps pumping a swing, the back-and-forth motion decreases; damping by the air's friction opposes the process is important for the write head that generates field pulses, the media that switch to record the field pulses as a magnetization pattern, and for the read head sensors
The most common technique to assess magnetization damping in magnetic films is to measure the ferromagnetic resonance Ferromagnetic resonance, or FMR, is a spectroscopic technique to probe the magnetization of ferromagnetic materials. It is a standard tool for probing spin waves and spin dynamics. It was unknowingly discovered by V. K. line width of the material. However, films of interest are seldom perfectly uniform, and meas-ured line width reflects both the damping and the defects in the sample. NIST (National Institute of Standards & Technology, Washington, DC, www.nist.gov) The standards-defining agency of the U.S. government, formerly the National Bureau of Standards. It is one of three agencies that fall under the Technology Administration (www.technology. researchers have developed a line width model that takes the defects into account and predicts the changes in line width that would be observed based on the type and strength of inhomogeneity in·ho·mo·ge·ne·i·ty n. pl. in·ho·mo·ge·ne·i·ties 1. Lack of homogeneity. 2. Something that is not homogeneous or uniform. Noun 1. . An earlier model of line width covers the limit of very small, weak defects where the magnetization is expected to behave mostly uniformly. In the opposite limit of strong, large defects, the magnetization was expected to behave differently in different parts of the film, but it has not been clear what size defect was necessary for this local behavior to take place. The new model bridges the theoretical gap between weak defect and strong defect limits and establishes the conditions needed for local behavior. The new model allows line width data to yield separate information about damping and non-uniformity, and for some data sets, limits may be placed on the defect sizes, thus allowing much better characterization A rather long and fancy word for analyzing a system or process and measuring its "characteristics." For example, a Web characterization would yield the number of current sites on the Web, types of sites, annual growth, etc. of magnetic recording media, heads, and other devices designed for GHz applications. CONTACT: Bob McMichael, (301)975-5121; robert. mcmichael@nist.gov. |
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