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We perform magnetoresistance (MR) and magneto-optical Kerr effect (MOKE) measurements to experimentally track magnetic domain wall (DW) pinning/depinning process in L-shaped Permalloy nanostructures of different geometries (i.e., square/round corner and absence/presence of circular disks) with widths in the range 75–400 nm. With MR and MOKE measurements being in a good quantitative agreement, we demonstrate that the field interval between pinning and depinning events increases with reduction of the nanowire width. In addition, the DW pinning/depinning behavior is geometry dependent, where round corners break the symmetry in the device orientation with respect to the field. The interpretation of experimental results is supported by micromagnetic simulations.

Using out-of-plane magnetized layers, a lateral shift register made from discrete elements is demonstrated. By carefully designing the in-plane shape of the elements which make up the shift register, both the position of nucleation of new domains and the coercivity of the element can be controlled. The dipole field from a neighbouring element placed tens of nanometers away creates a bias field on the nucleation site, which can be used to create a NOT gate. By chaining these NOT gates together, a shift register can be created where data bits consisting of neighbouring layers with aligned magnetization are propagated synchronously under a symmetric applied magnetic field. The operation of a 16 element shift register is shown, including field coupled data injection., This research is funded by the European Community under the Seventh Framework Program ERC Contract No. 247368: 3SPIN, and by EMRP JRP EXL04 SpinCal. The EMRP is jointly funded by the EMRP participating countries within EURAMET and the EU. AB acknowledges DTA funding from the EPSRC. A.F.-P. acknowledges support from the EPSRC Early Career Fellowship EP/M008517/1 and a Winton Fellowship.

Using out-of-plane magnetized layers, a lateral shift register made from discrete elements is demonstrated. By carefully designing the in-plane shape of the elements which make up the shift register, both the position of nucleation of new domains and the coercivity of the element can be controlled. The dipole field from a neighboring element, placed tens of nanometers away, creates a bias field on the nucleation site, which can be used to create a NOT gate. By chaining these NOT gates together, a shift register can be created where data bits consisting of neighboring layers with aligned magnetization are propagated synchronously under a symmetric applied magnetic field. The operation of a 16 element shift register is shown, including field coupled data injection.

Using Ga$^{+}$ focussed ion beam irradiation of Ta/Pt/CoFeB/Pt perpendicularly magnetized nanowires, the nucleation and injection fields of domain walls into the nanowires is controlled. The nucleation and injection fields can be varied as a function of dose, however, the range of injection fields is found to be limited by the creation of a step in anisotropy between the irradiated and unirradiated regions. This can be altered by defocussing the beam, which allows the injection fields to be further reduced. The ability to define an arbitrary dose profile allows domain walls to be injected at different fields either side of an asymmetrically irradiated area, which could form the initial stage of a logic device. The effect of the thickness of the magnetic layer and the thickness of a Ta underlayer on the dose required to remove the perpendicular anisotropy is also studied and is seen that for similar Ta underlayers the dose is determined by the thickness of the magnetic layer rather than its anisotropy. This finding is supported by some transport of ions in matter simulations.

The interaction of two domain walls (DWs) at a cross-shaped vertex fabricated from two ferromagnetic nanowires has been experimentally investigated. Both magnetostatically repulsive and attractive interactions have been probed. It is found that in the repulsive case, a passing DW may directly induce the depinning of another that is already pinned at a vertex. This effect can be qualitatively described by considering only simple, magnetostatic-charge-based arguments. In the attractive case, however, asymmetric pinning is found, with complete suppression of depinning possible. This observed effect is contrary to simple charge-based arguments and highlights the need for full micromagnetic characterization of the DW interactions in more complex systems.

The nucleation field of perpendicularly magnetized nanowires can be controlled by changing their width, so that below a critical width the nucleation field decreases as the width decreases. Placing pads at the ends of the nanowires prevents any reduction in coercivity with width, demonstrating that at small widths domain walls nucleate from the ends of the wires. Using this technique, we are able to create asymmetric nanowires with controlled nucleation at a defined point. We also show how dipole fields from a neighboring wire in close proximity can be used to shift the hysteresis loop of the asymmetric nanowire, creating a simple NOT gate. These results show how control of the in-plane shape of perpendicularly magnetized nanoscale elements can directly lead to device functionality.

Simultaneous anisotropic magnetoresistance and magneto-optical Kerr effect measurements have been performed on L-shaped Permalloy nanowires. It is shown that through magnetoresistance measurements at the corner of the device, the switching information of both arms in a single loop can be accessed. This is a very efficient method that allows for the characterization of the pinning properties in such a device as well as the understanding of the fundamental physics behind the nucleation and propagation processes in such a system. Experimental results are in good agreement with micromagnetic simulations.

Considerable difficulties exist in generating appreciable magnetic fields, localized on nanometer length scales for future experiments and technologies. Here we experimentally demonstrate selective reversal of a ferromagnetic nanowire by the stray field from a domain wall. The use of a domain wall as a persistent, mobile source of magnetic field is an alternative to localized Oersted fields and current induced switching, with possible use in future domain wall based data storage schemes and magnetic random access memory applications.

This study investigates the interaction between transverse head-to-head domain walls (THHDWs) in permalloy nanowires and magnetostatic charges located within a tripod structure in close proximity. This interaction enables remote pinning of the THHDW. Eight different interactions are measurable, depending on the initialising field sequence. The pinning strengths of an attractive potential well and a repulsive barrier are compared in this paper. Based on experimental measurements, micromagnetic simulations, and a monopolar analytical model, we demonstrate that pinning strength depends on the inhomogeneous charge distribution within the tripod and the relative orientation of the THHDW which faces the tripod.

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