FESEM images of AAO membrane (a) top view, and cross-sectional view filled with Co NWs with (b) L = 200 and (c) L = 400 nm. (d) X-ray diffraction patterns of Co NWs with varying L.
Measured M(H) loops of Co NW array for lengths (a) 200, (b) 400, and (c) 1000 nm for different θ values. (d) shows the measured Hc as a function of θ.
Simulated M(H) curves for different θ values: (a) L = 200 nm (with hcp (002) only), (b) L = 400 nm (with 300 nm of hcp (002) and 100 nm mix state of hcp (002) and hcp (100)), and (c) L = 1000 nm (with 300 nm of hcp (002), 200 nm mix state of hcp (002) and hcp (100) and remaining 500 nm of hcp (100)). Inset of (a) shows shearing of M(H) curve with increase in number, i, of NWs in the array structure. (d) Simulated Hc vs θ for different NW lengths.
(a) NW cylindrical shell at remanent state for L = 200 nm with hcp (002) structure showing the magnetic spins parallel to NW axis indicating a single domain magnetic state. (b) Comparison of Hc vs θ curves in case of NW with L = 200 nm calculated using Eq. (1) , and by micromagnetic simulation for single NW and seven NWs in a hexagonal array.
(a) NW cylindrical shell of L = 500 nm with hcp (100) structure at remanent state showing two vortices (clockwise and anti-clockwise) separated by a domain. (b) χ vs r around the middle of the NW with no vortex state at z = 250 nm. (c) χ vs r showing the decrease in vorticity with increasing the applied field H.
(a) NW cylindrical shell of L = 1000 nm with hcp (002) and (100) structures at remanent state. (b) The variation in χ with r, showing coherent structure (χ = 0°) at lower z values (z ≤ 400 nm) and the appearance of vortex for z > 400 nm. (c) Variation in χ with z indicating interaction region among two magnetic states along NW axis.
Different energy contributions in three cases of L = 200, 400, and 1000 nm at remanent state.
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