Single Diameter Modulation Effects on Ni Nanowire Array Magnetization Reversal

Abstract

Geometrically modulated magnetic nanowires are a simple yet efficient strategy to modify the magnetic domain wall propagation since a simple diameter modulation can achieve its pinning during the nanowire magnetization reversal. However, in dense systems of parallel nanowires, the stray fields arising at the diameter interface can interfere with the domain wall propagation in the neighboring nanowires. Therefore, the magnetic behavior of diameter-modulated nanowire arrays can be quite complex and depending on both short and long-range interaction fields, as well as the nanowire geometric dimensions. We applied the first-order reversal curve (FORC) method to bi-segmented Ni nanowire arrays varying the wide segment (45–65 nm diameter, 2.5–10.0 μm length). The FORC results indicate a magnetic behavior modification depending on its length/diameter aspect ratio. The distributions either exhibit a strong extension along the coercivity axis or a main distribution finishing by a fork feature, whereas the extension greatly reduces in amplitude. With the help of micromagnetic simulations, we propose that a low aspect ratio stabilizes pinned domain walls at the diameter modulation during the magnetization reversal. In this case, long-range axial interaction fields nucleate a domain wall at the nanowire extremities, while short-range ones could induce a nucleation at the diameter interface. However, regardless of the wide segment aspect ratio, the magnetization reversal is governed by the local radial stray fields of the modulation near null magnetization. Our findings demonstrate the capacity of distinguishing between complex magnetic behaviors involving convoluted interaction fields.

Direct Writing of Shape‐Gradient Magnetic Alloy Microwire Arrays with Meniscus‐Confined Electrodeposition Process

“…The remanence of the shape‐gradient array was increased from 0.007 to 0.045 compared with the uniform‐diameter array. As previously explained, [ 14 ] in continuous polycrystalline wires, the magnetization reversal mechanism is usually dominated by domain nucleation and motion, so some irreversibility (i. e. coercivity) is expected. When the field is applied perpendicular to the wire axis, the domains may no longer nucleate as the space of the wires gets smaller.…”

“…To realize shape gradient, Arzuza et al. [ 14 ] combined the three‐step anodization with an intermediate chemical etching step to modulate the wire diameter. Multisegmented nanowires with alternatively wide and narrow segments are obtained and showed complex magnetic behavior depending on both short and long‐range interaction fields, as well as the nanowire geometric dimensions.…”

“…Most importantly, only multisegmented magnetic nanowires with random diameter variations are achieved currently, which makes it difficult to analyze the magnetic testing results. [ 14 ] Therefore, finding a method that can prepare gradient micro/nanowire arrays with controllable morphology and composition will help to study the magnetic properties of the gradient magnetic alloy microwire arrays more scientifically.…”

“…Magnetic anisotropy is realized with the prepared wire arrays due to the alternating composition and crystalline structure of the individual segment. To realize shape gradient, Arzuza et al [14] combined the three-step anodization with an intermediate chemical etching step to modulate the wire diameter.Gradient magnetic micro/nanowire arrays have attracted widespread attention due to their interesting properties. However, fabricating such an ordered array of gradient micro/nanowires with controllable diameters and compositions is still a great challenge to most of the current methods.…”

“…Magnetic anisotropy is realized with the prepared wire arrays due to the alternating composition and crystalline structure of the individual segment. To realize shape gradient, Arzuza et al [14] combined the three-step anodization with an intermediate chemical etching step to modulate the wire diameter.…”