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: Guido Meier
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    • "Driven by a constant force in the presence of the quenched disorder, the interface moves with a steady-state velocity, while it is pinning when the force is weak compared to the random noise. Between them, there exists a secondorder dynamical phase transition, called as the " depinning transition " [1] [2] [3] [4] [5] [6] [7] [8]. For several decades, the depinining transition has been the focus of the experimental and theoretical research, which are common to a wide variety of phenomena, including the liquid invasion in porous media [9], the contact line in wetting [10], the vortices in type-II superconductors [11] [12], the charge-density waves [13], the fracture propagation [14] [15], the dislocation dynamics in crystal plasticity [16], and the domain-wall motions in ferromagnetic and ferroelectric materials [17] [18] [19] [20]. "
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    ABSTRACT: With the developed "extended Monte Calro" (EMC) algorithm, we have studied the depinning transition in Ising-type lattice models by extensive numerical simulations, taking the random-field Ising model with a driving field and the driven bond-diluted Ising model as examples. In comparison with the usual Monte Carlo method, the EMC algorithm exhibits greater efficiency of the simulations. Based on the short-time dynamic scaling form, both the transition field and critical exponents of the depinning transition are determined accurately via the large-scale simulations with the lattice size up to L = 8 912, significantly refining the results in earlier literature. In the strong-disorder regime, a new universality class of the Ising-type lattice model is unveiled with the exponents {\beta} = 0.304(5), {\nu} = 1.32(3), z = 1.12(1), and {\zeta} = 0.90(1), quite different from that of the quenched Edwards-Wilkinson equation.
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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.
    Full-text · Article · Jan 2012 · Journal of Physics Condensed Matter
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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.
    Full-text · Article · Jul 2010 · IEEE Transactions on Magnetics
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