We designed and fabricated a micro-scaled cell gripper based on two highly flexible magnetic zigzag structures that can be actuated by a magnetic field. Elongated single domain magnetic thin films with high magnetic shape anisotropy were deposited on the zigzag structures. By adjusting the external magnetic field we were able to control the torque applied on the magnetic films that was responsible for the actuation. We measured and discussed the displacement of the zigzag structures under different magnetic fields, and we observed a hysteresis characteristic in the actuation. Furthermore, we demonstrated the ability of gripping a single cell in water solution using the designed cell microgripper. The cell microgripper proposed in this study can provide important information for future biochip and biomedical applications.
2670 wileyonlinelibrary.com water droplet; [ 6 ] trichomes on the leaf surface are arranged with orientation to direct water droplets toward one end of the leaf to conserve water; [ 7 ] the wing surface of brown lacewing (Micromus tasmaniae) with microtrichia at different length-scale allow the insect to get through the wetted surfaces. [ 8 ] The above-mentioned surface all contain microscale geometry with special arrangement or topographies to infl uence the surface property. Specifi cally, leaf surface contains various trichomes that for some incline at an acute angle to guide water [ 7 ] while others retain water on leaves to improved photosynthetic environment. [ 9 ] Inspired by the peculiar trichome structures, this study attempted to adopt cone-shaped structures to systematically understand how the inclination of the trichome infl uences the wettability of leaves.Different strategies have been reported to obtain artifi cial microcone structures for the study of wetting property, including replica moulding, [ 2b , 10 ] laser irradiation, [11][12][13] reactive ion etching (RIE), [ 14,15 ] and chemical deposition. [ 16 ] However, the above methods are complicated or not fl exible enough to make microcones with tunable feature for our specifi c purpose. Previously, ferrofl uid-molding method, which made use of ferrofl uid as the master of the mother mold, has been demonstrated to fabricate microscale polymer arrays with controllable size. [ 17 ] In this study, we utilized the similar technique and further, modifi ed it for our particular purpose ( Figure 2 ). In the experiment, microcone structures with different inclination angle were generated by adjusting the direction of external magnetic fi eld applied to the ferrofl uid. Nickel thin fi lm was then deposited to give a nanoscale roughness layer. Wettability studies (contact angle, sliding angle) were analyzed, and the retention forces of droplet move against or along the orientation of cones were investigated. Results and DiscussionTo create cone-shaped structures resembling trichomes of plants, ferrofl uid-molding method was adopted. [ 17 ] As shown in Figure 3 a, the ferrofl uid was divided into microdroplets due to magnetic hydrodynamic instability and were arranged by the magnetic disks to form a hexagonal pattern. As the external Learning from nature, a series of cone-shaped structures resembling trichomes of plants are fabricated by ferrofl uid molding to understand the infl uence of geometry on wettability. Experimentally, ferrofl uid microdroplets are generated under an external magnetic fi eld, and their shape can be changed from right cones into oblique cones by tilting the external magnetic fi eld. Followed by hard molds made with UV-curable tri(propylene glycol) diacrylate, polydimethylsiloxane microcones with different inclination angle ( θ ) are subsequently generated. Nickel thin fi lm is deposited onto the microcones to form micro/nano dual-scale structures. The largest contact angle (CA) is obtained in nickel-deposited right cones (CA = 1...
We investigated the influence of magnetic domain walls and magnetic fields on the thermal conductivity of suspended magnetic nanowires. The thermal conductivity of the nanowires was obtained using steady-state Joule heating to measure the change in resistance caused by spontaneous heating. The results showed that the thermal conductivity coefficients of straight and wavy magnetic nanowires decreased with an increase in the magnetic domain wall number, implying that the scattering between magnons and domain walls hindered the heat transport process. In addition, we proved that the magnetic field considerably reduced the thermal conductivity of a magnetic nanowire. The influence of magnetic domain walls and magnetic fields on the thermal conductivity of polycrystalline magnetic nanowires can be attributed to the scattering of long-wavelength spin waves mediated by intergrain exchange coupling.
The magnetization reversal and the corresponding magnetoresistance of Permalloy rings are investigated here both numerically and experimentally. Micromagnetic simulations reveal that during the reversal process there exist three intermediate metastable states which lead to an unconventional triple-switching characteristic. Size effects are studied as well. The simulation results are in good agreement with our magnetoresistance measurements. Significant differences in the magnetoresistance at two orthogonal directions of the magnetic fields are observed and explained. An important contribution to the magnetoresistance due to the relative position of the domains and the current leads is also investigated.
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