Direct Observation of Stochastic Domain-Wall Depinning in Magnetic Nanowires

Center for X-ray Optics, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
Physical Review Letters (Impact Factor: 7.51). 05/2009; 102(14):147204. DOI: 10.1103/PhysRevLett.102.147204
Source: PubMed


The stochastic field-driven depinning of a domain wall pinned at a notch in a magnetic nanowire is directly observed using magnetic x-ray microscopy with high lateral resolution down to 15 nm. The depinning-field distribution in Ni80Fe20 nanowires considerably depends on the wire width and the notch depth. The difference in the multiplicity of domain-wall types generated in the vicinity of a notch is responsible for the observed dependence of the stochastic nature of the domain-wall depinning field on the wire width and the notch depth. Thus the random nature of the domain-wall depinning process is controllable by an appropriate design of the nanowire.

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Available from: Lars Bocklage, Oct 21, 2014
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    • "As a possible explanation for the stochastic nature of DW depinning fields, the thermal energy, the edge roughness, and the generation of different types of DW structures can be considered. In our previous work, we have found that the depinning fields are strongly related to the structures of DWs [8] "
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    ABSTRACT: Full-field magnetic transmission x-ray microscopy at high spatial resolution down to 20 nm is used to directly observe field-driven domain wall motion in notch-patterned permalloy nanowires. The depinning process of a domain wall around a notch exhibits a stochastic nature in most nanowires. The stochasticity of the domain wall depinning sensitively depends on the geometry of the nanowire such as the wire thickness, the wire width, and the notch depth. We propose an optimized design of the nanowire for deterministic domain wall depinning field at a notch.
    Journal of Physics Condensed Matter 01/2012; 24(2):024203. DOI:10.1088/0953-8984/24/2/024203 · 2.35 Impact Factor
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    • "shows a typical field distribution for pinning and depinning at the magnetic soft spot A. Note that the pinning field at spot A corresponds to the switching field of the wire without artificial pinning site. The broadness of the depinning field distribution underlines the stochastic nature of the DW depinning process [6]. We do not distinguish between different types of DWs like transverse and vortex walls. "
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    ABSTRACT: The local modification of magnetic properties by ion irradiation opens the possibility to create pinning sites for domain walls in magnetic nanowires without geometric constrictions. Implantation of chromium ions into Ni<sub>80</sub>Fe<sub>20</sub> nanowires is used to cause a local reduction of the saturation magnetization Ms and thus a decrease of the energy associated with the domain wall. Field-driven pinning and depinning of a domain wall at the here so-called magnetic soft spots is directly observed using magnetic transmission soft X-ray microscopy. The pinning rate and the depinning field considerably depend on the wire width and the chromium fluence.
    IEEE Transactions on Magnetics 07/2010; 46(6-46):1708 - 1710. DOI:10.1109/TMAG.2010.2042285 · 1.39 Impact Factor
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    ABSTRACT: Soft x-ray zone plate microscopy is a powerful nano-analytic technique used for a wide variety of scientific and technological studies. Pushing its spatial resolution to 10 nm and below is highly desired and feasible due to the short wavelength of soft x-rays. Instruments using Fresnel zone plate lenses achieve a spatial resolution approximately equal to the smallest, outer most zone width. We developed a double patterning zone plate fabrication process based on a high-resolution resist, hydrogen silsesquioxane (HSQ), to bypass the limitations of conventional single exposure fabrication to pattern density, such as finite beam size, scattering in resist and modest intrinsic resist contrast. To fabricate HSQ structures with zone widths in the order of 10 nm on gold plating base, a surface conditioning process with (3-mercaptopropyl) trimethoxysilane, 3-MPT, is used, which forms a homogeneous hydroxylation surface on gold surface and provides good anchoring for the desired HSQ structures. Using the new HSQ double patterning process, coupled with an internally developed, sub-pixel alignment algorithm, we have successfully fabricated in-house gold zone plates of 12 nm outer zones. Promising results for 10 nm zone plates have also been obtained. With the 12 nm zone plates, we have achieved a resolution of 12 nm using the full-field soft x-ray microscope, XM-1.
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