Papers by mostafa Alikhani
Nanoscale magnetic alloy wires are being actively investigated, providing fundamental insights in... more Nanoscale magnetic alloy wires are being actively investigated, providing fundamental insights into tuning properties in magnetic data storage and processing technologies. However, previous studies give trivial information about the crossover angle of magnetization reversal process in alloy nanowires (NWs). Here, magnetic alloy NW arrays with different compositions, composed of Fe, Co and Ni have been electrochemically deposited into hard-anodic aluminum oxide templates with a pore diameter of approximately 150 nm. Under optimized conditions of alumina barrier layer and deposition bath concentrations, the resulting alloy NWs with aspect ratio and saturation magnetization (M s) up to 550 and 1900 emu cm −3 , respectively, are systematically investigated in terms of composition, crystalline structure and magnetic properties. Using angular dependence of coercivity extracted from hysteresis loops, the reversal processes are evaluated, indicating non-monotonic behavior. The crossover angle (θ c) is found to depend on NW length and M s. At a constant M s , increasing NW length decreases θ c , thereby decreasing the involvement of vortex mode during the magnetization reversal process. On the other hand, decreasing M s decreases θ c in large aspect ratio (>300) alloy NWs. Phenomenologically, it is newly found that increasing Ni content in the composition decreases θ c. The angular first-order reversal curve (AFORC) measurements including the irreversibility of magnetization are also investigated to gain a more detailed insight into θ c .
Bookmarks Related papers MentionsView impact
FeCoNi nanowire arrays (175 nm in diameter and lengths ranging from 5 to 40 μm) were fabricated i... more FeCoNi nanowire arrays (175 nm in diameter and lengths ranging from 5 to 40 μm) were fabricated into nanopores of hard-anodized aluminum oxide templates using pulsed ac electrodeposition technique. Increasing the length had no considerable effect on the composition and crystalline characteristics of Fe 47 Co 38 Ni 15 nanowires (NWs). By eliminating the dendrites formed at the bottom of the pores, we report a careful investigation on the effect of magnetostatic interactions on magnetic properties and the effect of nanowire length on reversal modes. Hysteresis loop measurements indicated that increasing the length decreases coercivity and squareness values. On the other hand, first-order reversal curve measurements show a linear correlation between the magnetostatic interactions and length of NWs. Comparing reversal modes of the NWs both experimentally and theoretically using angular dependence of coercivity, we find that when L r22 μm, a vortex domain wall mode is only occurred. When L 422 μm, a non-monotonic behavior indicates a transition from the vortex to transverse domain wall propagation. As a result, a critical length was found above which the transition between the reversal modes is occurred due the enhanced interactions. The transition angle also shifts toward a lower angle as the length increases. Moreover, with increasing length from 22 to 31 μm, the single domain structure of NWs changes to a pseudo single domain state. A multidomain-like behavior is also found for the longest NWs length.
Bookmarks Related papers MentionsView impact
Keywords: Fe 80 Ni 20 nanowire arrays Angular first-order reversal curve Irreversible angular-dep... more Keywords: Fe 80 Ni 20 nanowire arrays Angular first-order reversal curve Irreversible angular-dependent coercivity Vortex domain wall Transverse domain wall Single vortex state a b s t r a c t The irreversible evolution of magnetic coercivity in arrays of 75 nm diameter Fe 80 Ni 20 nanowires (NWs) has been explored by means of first-order reversal curve (FORC) analysis as a function of the angle between the magnetic field and the NW axis (0° rθr 90°). The Fe 80 Ni 20 NWs with lengths up to 60 μm were fabricated using a pulsed electrodeposition method into hard-anodic aluminum oxide templates with an interpore distance of 275 nm. Investigating the interwire and intrawire magnetostatic interactions , the angular FORC (AFORC) diagrams indicated enhanced intrawire interactions with increasing length and θ (o 90°), induced by a magnetization reversal through vortex domain wall (VDW) propagation. Intriguingly, in addition to the VDW mode, a single vortex state with broad irreversible switching of nucleation and annihilation fields was detected at θ¼83° for 60 μm long NWs. At θ¼90°, the NWs reversed magnetization through transverse domain wall, involving a reversible component by a fraction of 95%. Furthermore, the transition angle between the reversal modes was found to decrease with increasing aspect ratio from 200 to 800. The irreversible angular-dependent coercivity (H c Irrev (θ)) of Fe 80 Ni 20 NWs was extracted from the AFORC measurements and compared with the major angular dependence of coercivity (H c Major (θ)) obtained from the conventional hysteresis loop measurements. While H c Major (θ) showed a non-monotonic behavior, H c Irrev (θ) constantly increased with increasing θ (o90°). On the other hand, using analytical models, a 93% agreement was obtained between the theoretical angular-dependent nucleation field and experimental H c Irrev (θ) for irreversible switching of VDW when 0° r θr86°.
Bookmarks Related papers MentionsView impact
Cobalt nanowire arrays were fabricated by ac (continuous and pulse) electrodeposition into anodic... more Cobalt nanowire arrays were fabricated by ac (continuous and pulse) electrodeposition into anodic aluminium oxide templates. The effects of continuous electrodeposition waveform and frequency as well as the pulse feature on the structure and magnetic properties of the nanowire arrays were studied. For continuous electrodeposition into the low depth nanohole, the microstructures and magnetic properties of the Co nanowires are independent of the waveform and frequency due to relatively rapid electrodeposition growth. The hcp Co nanowires with high crystallinity were fabricated using the pulse technique. More than 50 ms off-time between the pulses induces the preferentially growth direction of Co nanowires (the c-axis parallel to the wire axis), thereby improving the magnetic properties. A coercive force of 2370 Oe was obtained for Co nanowires fabricated with a pulse of 100 ms off-time and 5 ms reductive/oxidative time.
Bookmarks Related papers MentionsView impact
Materials Chemistry and Physics, 2008
Bookmarks Related papers MentionsView impact
Uploads
Papers by mostafa Alikhani