Current-induced resonance and mass determination of a single magnetic domain wall

Department of Physics, Keio University, Yokohama, 223-8522, Japan.
Nature (Impact Factor: 42.35). 11/2004; 432(7014):203-6. DOI: 10.1038/nature03009
Source: PubMed

ABSTRACT A magnetic domain wall (DW) is a spatially localized change of magnetization configuration in a magnet. This topological object has been predicted to behave at low energy as a composite particle with finite mass. This particle will couple directly with electric currents as well as magnetic fields, and its manipulation using electric currents is of particular interest with regard to the development of high-density magnetic memories. The DW mass sets the ultimate operation speed of these devices, but has yet to be determined experimentally. Here we report the direct observation of the dynamics of a single DW in a ferromagnetic nanowire, which demonstrates that such a topological particle has a very small but finite mass of 6.6 x 10(-23) kg. This measurement was realized by preparing a tunable DW potential in the nanowire, and detecting the resonance motion of the DW induced by an oscillating current. The resonance also allows low-current operation, which is crucial in device applications; a DW displacement of 10 microm was induced by a current density of 10(10) A m(-2).

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    • "The concept of magnetic charge is not exactly novel. It can be found in earlier research articles (Saitoh et al. 2004) and even in textbooks (Landau & Lifshitz 1984). Magnetic charges in spin ice are remarkable because they are mobile and represent a rare example of fractionalized excitations in three spatial dimensions: the underlying degrees of freedom, magnetic dipoles, must be split in half, so to speak, to create magnetic monopoles. "
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    Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences 12/2012; 370(1981):5718-37. DOI:10.1098/rsta.2011.0388 · 2.86 Impact Factor
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    • "The half-ring shape was designed for two reasons. First, it facilitates the DW creation [28]. As can be seen from the micromagnetic simulations presented on Fig.1 "
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    ABSTRACT: Shifting electrically a magnetic domain wall (DW) by the spin transfer mechanism is one of the future ways foreseen for the switching of spintronic memories or registers. The classical geometries where the current is injected in the plane of the magnetic layers suffer from a poor efficiency of the intrinsic torques acting on the DWs. A way to circumvent this problem is to use vertical current injection. In that case, theoretical calculations attribute the microscopic origin of DW displacements to the out-of-plane (field-like) spin transfer torque. Here we report experiments in which we controllably displace a DW in the planar electrode of a magnetic tunnel junction by vertical current injection. Our measurements confirm the major role of the out-of-plane spin torque for DW motion, and allow to quantify this term precisely. The involved current densities are about 100 times smaller than the one commonly observed with in-plane currents. Step by step resistance switching of the magnetic tunnel junction opens a new way for the realization of spintronic memristive devices.
    Nature Physics 02/2011; 7(8). DOI:10.1038/nphys1968 · 20.60 Impact Factor
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    • "The results show that domain-wall motion follows external magnetic field up to ~ 100 MHz while magnetization rotation does so all the way up to GHz. Theses results showed that RF field driven domain-wall motion is slow [22], which corroborates the current driven domain motion observation in [18]. On the other hand, the results in [23] [24] suggest that domain-wall motion is fast despite the lack of domain analysis and control. "
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    ABSTRACT: Incorporating ferromagnetic materials into integrated microwave devices is a promising approach for the development of on-chip high-performance circuit components. Therefore, high-frequency domain-wall motion and magnetization rotation, which yield permeability, are of primary interest. However, so far it has not been attempted to physically separate high-frequency domain-wall motion and magnetization rotation driven by external magnetic field excitation. Nor have attempts for the corresponding characterizations. In this work, patterned permalloy films are integrated with on-chip microstrip lines. Domain-wall motion and magnetization rotation are separated through aspect ratio and dimension control. The measured results show that high-frequency-field driven domain-wall motion is fast, different from current driven domain-wall motion. It is also shown that coupling effects are not important when the distance between two adjacent permalloy films is ~ 1 μm despite their large lateral dimensions. Finally, surface topography affects domain structures and corresponding dynamic processes.
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