Instability of bubble radial motion associated with chirality changes

Zimmermann, Lars; Miltat, J.

doi:10.1016/0304-8853(91)90129-x

Cited by 7 publications

(1 citation statement)

References 14 publications

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“…Depending on the driving force, conventionally magnetic field and, more recently, spin-polarized current [4][5][6][7][8][9][10][11][12][13] , the propagation of DWs changes from a simple translation to more complex precessional modes 14 . Experimentally, indirect evidence of this transition is found from a sudden drop in the wall's velocity [15][16][17][18] , but direct observation of the precessional modes is lacking. Here we show experimentally, using a combination of quasi-static and real-time measurement techniques, that DWs propagate along permalloy nanowires with a periodic variation in the chirality of the walls.…”

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confidence: 99%

Direct observation of the coherent precession of magnetic domain walls propagating along permalloy nanowires

et al. 2006

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The dynamics of the motion of domain walls (DWs) in magnetic materials has been extensively explored theoretically 1-3 . Depending on the driving force, conventionally magnetic field and, more recently, spin-polarized current 4-13 , the propagation of DWs changes from a simple translation to more complex precessional modes 14 . Experimentally, indirect evidence of this transition is found from a sudden drop in the wall's velocity [15][16][17][18] , but direct observation of the precessional modes is lacking. Here we show experimentally, using a combination of quasi-static and real-time measurement techniques, that DWs propagate along permalloy nanowires with a periodic variation in the chirality of the walls. The frequency of this oscillation is consistent with a precession of the propagating DW, increasing linearly with field according to the Larmor precession frequency. Current in the nanowire, large enough to significantly influence the DW velocity 18,19 , has little effect on the precession frequency but can be used to adjust the phase of the wall's precession. The highly coherent and reproducible motion of the DW revealed by our studies demonstrates that the DW is a well-defined macroscopic object whose phase is inextricably interlinked to the distance travelled by the DW.With the advent of magnetic nanowires of dimensions comparable to magnetic DW widths, it is possible to imagine that DWs propagating along such wires will exhibit a well-defined precessional mode due to confinement. In contrast, in extended structures, which have been extensively studied in the past, many modes are accessible 1,20 . Permalloy nanowires are attractive because they exhibit large anisotropic magnetoresistance (AMR) so that transverse and vortex walls can be readily detected and identified by resistance measurements. Furthermore, by breaking the onedimensional symmetry of the nanowire with a notch along one of its edges, the chirality of the DW can also be discerned 21 . Here, notched nanowires are used to directly show that the chirality of transverse DWs periodically reverses as the walls propagate in the precessional regime. This precessional motion is also detected in real time using time-resolved resistance measurements, which show that the precessional motion is, surprisingly, highly coherent.A scanning electron microscopy image of a typical permalloy nanowire with two contact lines, labelled A and B, is shown in Fig. 1a. Using a suitable field sequence (see the Methods section), a DW is introduced into section A-B of the nanowire by injecting a voltage pulse into contact line A. A magnetic field, H, is applied along the wire during the voltage pulse injection to assist the subsequent propagation of a DW. A fraction of the injected voltage pulse flows into section A-B, thereby injecting current into the nanowire as the DW propagates along it. The current density that flows into the nanowire scales as ∼0.5 × 10 8 A cm −2 V −1 . Positive current is defined as current flowing from line A to B.The existence of a DW in sectio...

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