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DOI: 10.1126/science.1092905 , 422 (2004); 304 Science et al. Lei Lu, in Copper Ultrahigh Strength and High Electrical Conductivity (this information is current as of August 27, 2008 ): The following resources related to this article are available online at version of this article at: including high-resolution figures, can be found in the online Updated information and services, can be found at: Supporting Online Material 126 article(s) on the ISI Web of Science. cited by This article has been 3 articles hosted by HighWire Press; see: cited by This article has been Materials Science : subject collections This article appears in the following in whole or in part can be found at: this article permission to reproduce of this article or about obtaining reprints Information about obtaining registered trademark of AAAS. is a Science 2004 by the American Association for the Advancement of Science; all rights reserved. The title Copyright American Association for the Advancement of Science, 1200 New York Avenue NW, Washington, DC 20005. (print ISSN 0036-8075; online ISSN 1095-9203) is published weekly, except the last week in December, by the Science on August 27, 2008 Downloaded from
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magnetic fields and moments in a right- handed coordinate system. It does not im- ply a broken parity. Micromagnetic simu- lations of the core motion during the first 3 ns are shown in Fig. 2 (B and C) ( 13 ). During the external field pulse, the core moves either parallel or antiparallel to the field, depending on the vortex handedness. Afterward, the trajectory turns parallel or antiparallel to the magnetostatic field and the core starts its gyrotropic motion, in agreement with the experiment. A first estimate of the field H that is driving the vortex motion can be made with the vortex susceptibility ± , which relates the in-plane magnetization density m d to the field H for a given displacement of the core d , according to ± H ² m d ² d / l ± M s . The magne- tization density is a linear function of the displacement d , where M s is the saturation magnetization. We considered a square vor- tex of length l ² 1 ³ m, for which the vortex susceptibility has been determined by simu- lations to be ´ 4 µ 10 5 henries per meter in agreement with experiments ( 14 ). For the observed vortex displacement d ² 50 nm, the resulting average internal field is H ² 3 mT. Assuming that this field powers the gyro- tropic motion of the vortex center, the speed V of the core can be estimated using V 2 · bH / ¸ . This formula reflects that the pre- cession of core spins by ¸ /2 corresponds to the translation of the core by its diameter b. · is the gyromagnetic ratio. Therefore, using b ² 10 nm ( 15 ), we expected a vortex speed of ´ 4 m/s. However, the experimentally de- termined vortex speed after the field pulse was close to 100 m/s (Fig. 3). This leads us to
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