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The potential experienced by transverse domain walls (TDWs) in the vicinity of asymmetric constrictions or protrusions in thin Permalloy nanowires is probed using spatially resolved magnetooptical Kerr effect measurements. Both types of traps are found to act as pinning centers for DWs. The strength of pinning is found to depend on the trap type as well as on the chirality of the incoming DW; both types of traps are seen to act either as potential wells or potential barriers, also depending on the chirality of the DW. Micromagnetic simulations have been performed that are in good qualitative agreement with the experimental results.

Modern fabrication technology has enabled the study of submicron ferromagnetic strips with a particularly simple domain structure, allowing single, well-defined domain walls to be isolated and characterized. However, these domain walls have complex field-driven dynamics. The wall velocity initially increases with field, but above a certain threshold the domain wall abruptly slows down, accompanied by periodic transformations of the domain wall structure. This behaviour is potentially detrimental to the speed and proper functioning of proposed domain-wall-based devices, and although methods for suppression of the breakdown have been demonstrated in simulations, a convincing experimental demonstration is lacking. Here, we show experimentally that a series of cross-shaped traps acts to prevent transformations of the domain wall structure and increase the domain wall velocity by a factor of four compared to the maximum velocity on a plain strip. Our results suggest a route to faster and more reliable domain wall devices for memory, logic and sensing.

The magnetostatic interaction between two oppositely charged transverse domain walls (DWs) in adjacent Permalloy nanowires is experimentally demonstrated. The dependence of the pinning strength on wire separation is investigated for distances between 13 and 125 nm, and depinning fields up to 93 Oe are measured. The results can be described fully by considering the interaction between the full complex distribution of magnetic charge within rigid, isolated DWs. This suggests the DW internal structure is not appreciably disturbed by the pinning potential, and that they remain rigid although the pinning strength is significant. This work demonstrates the possibility of non-contact DW trapping without DW perturbation and full continuous flexibility of the pinning potential type and strength. The consequence of the interaction on DW based data storage schemes is evaluated.PACS numbers: 75.75.+a, 75.60.Ch, 85.70.Kh, 75.60.Jk Quantifying the interaction between magnetic domain walls (DWs) in closely packed networks of ferromagnetic nanowires is of vital importance to recently proposed DW based logic and data storage schemes [1,2], as these interactions could potentially compromise coherent DW propagation and correct device function. In addition to these schemes, DWs in nanowires have also been suggested for use in a wide range of applications, such as atom trapping for quantum information processing [3]. Furthermore, the fundamental properties of DWs themselves are attracting great interest, and DWs can be considered not only as transition regions between oppositely magnetized domains, but as quasi-particles [4]. Their equilibrium [5], dynamic properties [6,7,8,9] and interactions with artificial defects [10] are being intensively studied. The ability to hold DWs at defined positions is required for a wide range of spin torque experiments, where current is used to depin the DWs; a continuously variable pinning strength which does not alter the current path is highly desirable in such cases [11]. The possibility of a well defined, tunable pinning potential where the DW acts as a truly rigid quasi-particle is also appealing, for example, in current induced resonance experiments [12,13]. The effect of the presence of a transverse DW (TDW) in a nearby structure on the magnetic state of a ferromagnetic ring has been reported [14,15], and quantified in terms of an additional local field due to the TDW stray field, but no quantitative analysis of the full pinning potential created by a DW on another DW has been made.In this paper, we experimentally study the interaction between two oppositely charged DWs travelling in two parallel Permalloy (Py) nanowires and its dependence on wire separation. The separations probed in this investigation are below the dimensions of the DW (∼ 100nm) itself and so are within the near-field limit. By considering the full, rigid magnetostatic charge distribution of an isolated DW we are able to reproduce fully the experimental results. This suggests the internal structure of the DW is not appre...

The motion of transverse domain walls (DWs) in thin Permalloy nanowires has been studied by locally detecting the chirality of the moving DW, using a cross-shaped trap acting as a chirality filter. We find that structural changes of the DW occur over a characteristic minimum distance: the ''DW fidelity length.'' The measured field dependence of the fidelity length is in good qualitative agreement with a 1D analytical model and with published results of numerical simulations and experiments. We also demonstrate extension of the fidelity length to meter length scales using a series of filters. DOI: 10.1103/PhysRevLett.102.057209 PACS numbers: 75.75.+a, 75.60.Ch, 75.60.Jk, 85.70.Kh The controllable motion of magnetic domain walls (DWs) in nanoscale conduits is fundamental to the operation of new magnetic logic and data storage devices [1,2]. In particular, changes of the DW structure are significant in device applications where DW motion is controlled via interaction with artificial defects, because the detailed spin distribution in the wall affects the nature and strength of the pinning potential [3]; the fidelity of data transmission may then depend on preserving the DW structure. Simulations predict that for thin and narrow nanowires, the equilibrium wall structure is a transverse DW [4,5] characterized by a charge (head to head or tail to tail) and a chirality (defined by the sense of rotation of spins in the wall). The dynamics of a single DW can be qualitatively described using analytical models [6][7][8], which predict two regimes of motion: viscous below a critical ''Walker field'' and oscillatory above it. In the particular case of a transverse DW in a nanostrip, full micromagnetic simulations are necessary to elucidate the details of the wall motion and show that the oscillation of the DW structure proceeds via successive nucleation and annihilation of antivortices, leading to periodic transformations between transverse DWs of opposite chirality. For device applications it is necessary to know the length scale over which the chirality is predictable in a real system. Experimentally, such behavior is difficult to measure because the evolution of the DW structure occurs on nanosecond time scales and the absolute moment of the DW is small (on the order of 10 À13 emu); however, temporal oscillations of the nanowire resistance (due to the anisotropic magnetoresistance effect) have been observed, corresponding to periodic transformations of the DW structure [9], and the DW velocity oscillation which accompanies the structural transformations has been detected using time-resolved magneto-optical Kerr effect (MOKE) measurements [10]. In this Letter, we demonstrate direct spatial measurements of the position dependence of the DW structure as it propagates along such wires. We construct a ''chirality filter'' consisting of a cross-shaped trap, which allows us not only to detect the DW chirality but also to reset it. We find that transformations of the DW structure occur over a characteristic distance which we c...