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A combinatory two-step anodization technique is presented to prepare self-ordered porous anodic alumina (PAO) templates. The first and second anodization steps are performed in oxalic and selenic acid at 40 V and 45 V, respectively, giving rise to 13-nm-diameter PAOs with high ordering and porosity of 1.4%. The anodization time for the second step is also changed to investigate the effect of the oxide layer thickness on the pore ordering, using field-emission scanning electron microscopy and fast Fourier transform analyses. Increasing the anodization time from 20 min to 1 h considerably improved the ordering and hexagonal domain structures. Further increasing the anodization time up to 8 h continuously deteriorated the ordering of the PAOs, although the nanopore growth rate remained almost constant. The fabrication of small-diameter PAOs in selenic acid is discussed and related to the electric field concentration at the oxide–electrolyte interface at the bottom of pores.

Zinc oxide nanorods (NRs) were successfully synthesized on the seeded substrate by low-temperature hydrothermal method. The effect of adding ZnO nanoparticles (NPs) to hydrothermal bath on the structural, morphological, and electrical properties of the resulting NRs was systematically investigated. The NRs diameter and length decrease with increasing amount of NPs added to hydrothermal solution thereby confirmed NPs efficiently able to etch ZnO NRs. XRD analysis revealed that all the ZnO NRs have the hexagonal wurtzite structure with a preferential orientation along the c-axis. The I–V measurement illustrated a remarkable increment in electrical resistance of ZnO NRs due to morphological changes in the etched NRs. Photoconducting properties of ultraviolet (UV) detectors based ZnO NRs were also evaluated. It was observed that sensitivity of photodetectors increases to value of ~2 × 104 in NRs etched with 0.03 g/L NPs concentration.

In this work, a (ZnO)/(Cu-doped ZnO) core/shell nanorods array was fabricated by a two-step method: ZnO hydrothermal synthesis followed by encapsulation via a dip-coating process. The effects of the Cu dopant concentration on the structural, electrical and optical properties of the nanorods were studied. The SEM images showed that the encapsulation increased the nanorods average diameter from ~40 to ~60 nm. All ZnO core/shell nanorods showed a hexagonal wurtzite structure with no trace of a Cu oxide phase. A peak shift was observed in the XRD pattern, indicating the better Cu+ substitution into the Zn sites. The I–V measurements also showed that Cu doping up to 4.5 at.% decreased the samples resistance, which could be attributed to the +1 valance state of the Cu ions. It was also found that Cu doping increased the UV photoresponsivity of the photodetectors made by Cu:ZnO.

From fast magnetic memories with low-power consumption to recording media with high densities, realizing the magnetization reversal and interaction of magnetic layers would allow for manipulating the ultimate properties. Here, we use a pulsed electrochemical deposition technique in porous alumina templates (50 nm in pore diameter) to fabricate arrays of nanowires, consisting of FeNi layers (26−227 nm in thickness) with disk to rod-shaped morphologies separated by ultra-thin (3 nm) Cu layers. By acquiring hysteresis curves and first-order reversal curves (FORCs) of the multilayer nanowire arrays, we comprehensively investigate magnetization reversal properties and magnetostatic interactions of the layers at different field angles (0° ≤ θ ≤ 90°). These involve the extraction of several parameters, including hysteresis curve coercivity (H c Hyst ), FORC coercivity (H c FORC ), interaction field distribution width (ΔH u ), and irreversible fraction of magnetization (IF m ) as a function of θ. We find relatively constant and continuously decreasing trends of H c Hyst when 0° ≤ θ ≤ 45°, and 45° θ ≤ 90°, respectively. Meanwhile, angular dependence of H c FORC and IF m shows continuously increasing and decreasing trends, irrespective of the FeNi layer morphology. Our FORC results indicate the magnetization reversal properties of the FeNi/Cu nanowires are accompanied with vortex domain wall and single vortex modes, especially at high field angles. The rod-shaped layers also induce maximum ΔH u during the reversal process, owing to enhancements in both magnetizing and demagnetizing-type magnetostatic interactions.

Metal nanowires (MNWs) have gained considerable attention from research groups as they can be effectively applied in new transparent conductive electrodes (TCEs), replacing indium tin oxide (ITO) materials. However, using conventional synthetic methods including the chemical solution, Ag and Cu NW-based TCEs have been found to be non-uniform and unstable in reactive environments. Here, we present an innovative high-throughput method in the fabrication of Ni, AgNi, AgCu and AgNiCu NW-based TCEs using the electrodeposition of metal ions into anodic aluminum oxide (AAO) templates, followed by drop-coating of highly uniform MNWs on glass substrates. After the complete release of 60 μm long MNWs with high crystallinity from the templates, the resulting TCEs show enhanced electrical, optical and chemical stability properties compared to those of ITOs and Ag NW-based TCEs. Notably, in the case of Ag98Ni1Cu1 NW-based TCEs, we obtain a low sheet resistance of 36 Ω sq.−1 together with a high transparency of 88%, thereby evidencing the fabrication of high-quality TCEs without byproducts and difficult post-treatments. These MNW-based TCEs are also exposed to sulfurization environment, showing chemical stability with no precedent in the literature. Keywords: Transparent conductive electrodes, Metal nanowires, Ag-based nanowires, Electrodeposition, Anodic aluminum oxide template, Sulfurization environment

Realizing promising materials for use in next-generation devices at the nanoscale is of enormous importance from both fundamental and applied perspectives. Nonmagnetic and magnetic metal nanowire (NW) arrays fabricated by template-based electrodeposition techniques have long been considered as good candidates for this purpose. In this review, we focus on the fabrication techniques and characterizations of electrochemically deposited NWs with single, binary, ternary and multilayered component structures mostly carried out in our group. Particular attention is paid to the crystalline and magnetic characteristics (coercivity, squareness, magnetic phase, interactions and magnetization reversal modes) of NW arrays embedded in mild and hard anodized anodic aluminum oxide (AAO) templates with different pore diameters. The pulsed alternating current electrodeposition technique is proposed as a versatile approach in high-efficiency filling of the AAO templates, while also allowing for tuning magnetic properties of the resultant NWs. The first-order reversal curve analysis is also highlighted as an advanced characterization tool for nanomagnet arrays. Finally, potential cutting-edge nanoscale applications (magnetic information storage, energy storage and conversion, electronics, biosensing, microwave absorption and giant magnetoresistance) of magnetic NWs are presented.

While Co ferrite nanoparticles (NPs) have been widely considered for potential applications in magnetic storage, photocatalysts, and hyperthermia, significantly less attention has been paid to explore their detailed magnetic characteristics as a function of the Co content. Herein, a hydrothermal method was successfully used for the preparation of CoxFe3−xO4 (0.5 ≤ x ≤ 2) NPs, employing stable ferric and cobalt salts with PVP surfactant as a capping agent. Hysteresis loop measurements showed maximum coercivity (Hc) and saturation magnetization (Ms) of 982 Oe and 46 emu/g for Co0.5Fe2.5O4 and CoFe2O4 compounds, respectively. Detailed magnetic characteristics of the resulting NPs with different morphologies ranging from nanocubes to dense nanospheres were comprehensively investigated by first-order reversal curve analysis. It was found that CoxFe3−xO4 (0.5 ≤ x

Three-dimensional ZnO nanorods (NRs) were synthesized by hydrothermal method on ZnO seed layer including horizontal ZnO NRs. The ZnO seed layers consist of different values of NRs were synthesized by spin-coating. The different seed layers and ZnO nanorods arrays were characterized using field emission scanning electron microscopy, X-ray diffraction. Horizontally dispersed NRs on the substrate formed an overlapping junction structure into seed layer as ZnO NRs network. NRs grown on the seed layer including horizontal NRs were oriented in different directions to form three-dimensional ZnO NRs in flower shape. The electrical resistance of sensors based NRs array decreased dramatically with increasing NRs added to ZnO seed layer. Results show that ultraviolet photocurrent increased from 1.7 to 23 μA which is suitable for fabrication of practical photodevices.

Ordered arrays of NiFe/Cu multisegmented nanowires (NWs) are fabricated by ac pulse electrodeposition method into the 25-µm thick anodic aluminum oxide templates with a pore diameter of about 40–100 nm inter-pore distance. The behavior of magnetostatic interactions between neighboring NiFe/Cu NWs as well between magnetic segments of the same wire related to the NW length and the magnetic segment thickness is presented. The first-order reversal curves (FORCs) results for two given magnetic shape anisotropies, a nearly disk-shaped and a rod-shaped one, reveal a single domain magnetic state along with a constant peak value of FORC coercivity distribution (H FORC ). However, the Major Hysteresis Loop coercivity (H MHL ) shows a significant reduction with an increase in length. In addition, the magnetostatic interaction distribution along the Hu axis of FORC diagrams shows a weakly decreasing behavior, in disagreement with existing phenomenological model. In order to resolve this contradiction, the reversible and irreversible components of magnetization were measured. For arrays of multisegmented NWs, the contribution of the reversible components of magnetization rises up to about 70% as NW’s length increases which is in contrast for arrays of uniform NWs where a nearly zero reversibility is reported.

ZnO nanorods (NRs) were successfully synthesized on seed layered substrate by a rotational hydrothermal method. The critical role of initial rest time of rotating substrate on the growth and UV photodetecting properties of ZnO NRs was systematically investigated. Moreover, the crystal structure and morphology of as-grown ZnO NRs were characterized by X-ray diffraction and field emission scanning electron microscopy, respectively. The XRD studies showed that the c-oriented (002) peak of ZnO NRs was shifted towards higher values with increasing initial rest time while the grain size decreased. Interestingly, the diameter and length of NRs displayed increasing trend with increasing the initial rest time which makes them tunable nanostructures through facile hydrothermal-based fabrication process. The change in the electrical resistance of the samples was described according to morphological specification of NRs and buffer layer thickness which was ascribed to the transport mechanism of electrons in the synthesized buffer layer. Finally, photosensing properties of ZnO based ultraviolet (UV) detectors were evaluated. Accordingly, it was observed the photodetector with optimal performance (20 min initial time) shows an optimum sensitivity of ~ 1270 and responsivity of ~ 1.18 A/W.

ZnO nanorods (NRs) were successfully synthesized on seed layered substrate by a novel rotational hydrothermal method. The effect of substrate rotational speed on the growth of ZnO NRs were systematically characterized by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). With an increase of the rotational speed, the mean diameter of the ZnO NRs decreased from ~ 43 nm in ZnO NRs grown on a steady substrate to ~27 nm in a sample with 60 rpm while the number density was increased about one order. The optical studies indicated that band gap of ZnO NRs was shifted towards higher values with increasing speed up to 60 rpm and then decreases gradually. The electrical resistance variation of samples was described according to structural properties of NRs and their coalescence, where the increasing of NRs lateral junction through substrate rotation, improves the electrons transition in samples. Finally, photosensing properties of ZnO based ultraviolet (UV) detectors were investigated. It was observed that the photdetector based on ZnO NRs grown at 120 rpm shows an optimum performance with sensitivity 570 and responsivity 1.9 A/W.

Novel synthetic methods and materials tuned for high-efficiency absorbers are increasingly being used for shielding environments from microwaves with frequencies of gigahertz range emitted from cell phones and radar systems. Here, an in situ precipitation route in the synthesis of nanocomposites consisting of magnetic alloy FeNi and semiconductor ZnO nanoparticles (NPs) with different FeNi/ZnO ratios (1:1, 1:2, and 2:1) is presented. The resulting nanocomposites were employed as electromagnetic wave absorbers in the microwave range, and their structural and magnetic properties were investigated. Scanning and transmission electron microscopic analyses of FeNi/ZnO NP composites (NPCs) revealed crystalline particulates with spherical and conical morphology. Saturation magnetization and coercivity significantly increased to 161 Oe and 90 emu/g after performing an annealing process, starting from 77 Oe and 26 emu/g for as-synthesized (FeNi)2/(ZnO)1 NPC. In this case, a high reflection loss of −37.3 dB at 11.8 GHz was obtained for the NPC with an optimum thickness of 1.6 mm. Our calculations indicate that the eddy current effect plays a crucial role in the electromagnetic loss of magnetic alloy/semiconductor NPCs.

In this study, we fabricated ZnO nanorods grown on Fe-doped ZnO seed layer by a hydrothermal method. The effects of seed layer on growth of ZnO nanorods and their electrical and photodetection properties were systematically investigated. Results indicate that the average diameter of ZnO nanorods decreases with increasing Fe concentration while the nanorods number density has an increasing trend. The X-ray analysis showed that there is a preferred growth orientation rods in all samples. The electrical resistance of ZnO NRs reduces with increasing of Fe dopant up to 1.5 at.% and then increases with 4.5% Fe in seed layer. Also, the photodetection performance of ZnO nanorod-based photodetectors grown on the Fe-doped seed layer improved as sensitivity increased ∼377 for the sample grown on ZnO seed layer with 4.5 at.% Fe dopant under ultraviolet illumination and the responsivity increased ∼18.6 A/W for sensor including seed layer with 1.5 at.% Fe.

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 .

Magnetic nanowires electrodeposited into solid templates are of high interest due to their tunable properties which are required for magnetic recording media and spintronic devices. Here, highly ordered arrays of FeCoNi NWs with varied diameters (between 60 and 150 nm) were fabricated into nanopores of hard-anodized aluminum oxide templates using pulsed ac electrodeposition technique. X-ray diffraction patterns indicated the formation of FeCoNi NWs with fcc FeNi and bcc FeCo alloy phases, being highly textured along the bcc [110] direction. Magnetic properties were studied by hysteresis loop measurements at room temperature and they showed reductions in coercivity and squareness values by increasing diameter. First-order reversal curve measurements revealed that, with increasing diameter from 60 to 150 nm, besides a transition from a single domain (SD) state to a pseudo SD state, an increase in the reversible magnetization component of the NWs from 11% to 24% occurred.

This study aims to overcome a major challenge that is reaching high pore-filling percentage (FP) in the fabrication of high aspect ratio (HAR) nanowires (NWs) grown electrochemically in large diameter porous templates. By ultrathinning the barrier layer of hard anodized anodic aluminum oxide (AAO) templates with large pore diameters (Dp) of 110 and 180 nm, while also filling its branched sections with FeCoNi, the development of Cu FP was investigated for different Cu solution concentration (MCu = 0.05–0.3 M) in the fabrication of HAR Cu NW arrays using a pulsed electrochemical deposition technique under optimized parameters. At Dp = 180 nm, field-emission scanning electron microscopic investigations revealed that, increasing MCu increases the corresponding FP up to 62%, resulting in highly uniform NW arrays. Structural properties were investigated by X-ray diffraction analysis, indicating that different phase percentages of Cu and Cu2O are formed depending on Dp of AAO and MCu. The resulting HAR Cu NWs were also released from the hard templates to obtain free-standing NW arrays with a length of 70 μm, which may find potential use for large-scale nanodevice applications.

In this paper, Fe-doped ZnO/ZnO shell/core nanostructures were synthesized through a simple two-step method and the effects of Fe dopant concentrations (between 0 and 9 at%) on the structural, optical, electrical and gas sensing properties were investigated. The X-ray diffraction analysis revealed that all of the samples are crystallized in the same wurtzite hexagonal crystal structure with (002) peak as the main orientation. Nevertheless, the morphology of shell/core nanorods remained stable with increasing of Fe dopant, but the crystallinity improved. The ultraviolet–visible spectroscopy analysis showed that the Fe ions have coordination number of 3+ in the ZnO shell layer. The participation of Fe 3+ ions into ZnO layer was also confirmed by Current–Voltage (I–V) curves where the resistance of nanorods was reduced with Fe concentration. Moreover, the ethanol-sensing properties of the Fe-doped ZnO/ZnO shell/core nanorod sensors were systematically investigated. According to the results, optimum gas sensing was obtained by the addition of 0.5 at% Fe to ZnO shell layer which lead to significant enhancement in ethanol gas response.

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°≤ θ ≤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 ( θ =83° for 60 μm long NWs. At θ =90°, 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 ( H c Irrev ( θ ) for irreversible switching of VDW when 0°≤ θ ≤86°.

Arrays of multilayered Ni/Cu nanowires (NWs) with variable segment sizes were fabricated into anodic aluminum oxide templates using a pulsed electrodeposition method in a single bath for designated potential pulse times. Increasing the pulse time between 0.125 and 2 s in the electrodeposition of Ni enabled the formation of segments with thicknesses ranging from 25 to 280 nm and 10–110 nm in 42 and 65 nm diameter NWs, respectively, leading to disk-shaped, rod-shaped and/or near wire-shaped geometries. Using hysteresis loop measurements at room temperature, the axial and perpendicular magnetic properties were investigated. Regardless of the segment geometry, the axial coercivity and squareness significantly increased with increasing Ni segment thickness, in agreement with a decrease in calculated demagnetizing factors along the NW length. On the contrary, the perpendicular magnetic properties were found to be independent of the pulse times, indicating a competition between the intrawire interactions and the shape demagnetizing field.

ZnO nanorod (NR) arrays were grown by a simple two-step chemical bath deposition method. The as-deposited NRs were then annealed at different temperatures (300, 400 and 500 °C) for two time durations (1 and 5 h). The NRs were studied by scanning electron microscopy, photoluminescence spectroscopy, X-ray diffraction and two-point electrical test. Finally, ultraviolet (UV) detection properties of samples as an active layer in UV photodetector devices were evaluated. The structural results showed that the sample annealed at 400 °C had the best crystallinity. Furthermore, it was seen that the optical transparency and band gap of NRs increased with increase of the annealing temperature up to 400 °C and then decreased at 500 °C. The electrical resistance decreases with increment of the annealing temperature due to intensive desorption of oxygen molecules from the surface of ZnO NRs. The UV detection results proved a meaningful relevance of UV detection properties with the density of defects and quantity of oxygen molecules absorbed on the surface. ZnO NRs annealed at 300 °C for 1 h had the highest photosensitivity of ∼300 and photoresponsivity of 2.067 A/W which make it suitable for the practical applications.

A new approach to tuning the crystalline characteristics and magnetic properties of cobalt nanowire (NW) arrays embedded in AAO templates is reported using zinc additive. This is realized by adding low concentrations of Zn when pulse-electrodepositing cobalt NWs while also increasing the solution pH from 3 to 5. Using hysteresis loop measurements with a magnetic field applied parallel to the NW axis, coercivity and squareness of pure cobalt NWs increased from 890 Oe and 0.45 to 2150 Oe and 0.93 in Co 97 Zn 3 NWs, respectively, using a Zn concentration of 0.01 M at pH = 4. XRD patterns obtained from the cobalt-rich CoZn NWs revealed that the crystalline texture of cobalt changes from [1 0 0] direction to [1 0 1] and [0 0 2] at pH = 3 and 4, respectively. For the latter, the magnetocrystalline easy axis of cobalt rotates from nearly perpendicular to parallel to the NW axis, induced by the incorporation of zinc into the hcp structure of cobalt.

The effect of interactions on the soft and hard phases and interference region that commonly appears in the First Order Reversal Curve (FORC) of interacting two-phase magnetic systems was investigated. To obtain an interacting two-phase system, a new method was introduced for the first time to electrodeposit a two-phase magnetic nanowire (NW) composed of hard and soft phases with high magnetization into nanopores of the anodized aluminum oxide template using the single-bath ac-pulse electrodeposition technique. Two-phase behavior was obtained by multilayer and grainy configurations of the CoFe and Cu layers as two type layers with controllable thickness through the related pulse numbers. It was found that interphase interaction can be observed in FORC diagrams with three factors; (i) the shift in center of the soft phase feature along the interaction field axis without the change in coercivity, (ii) shift in center of the hard phase feature along the coercivity axis and (iii) appearance of an additional interference region. However, order of the shifts directly correlates with the order of demagnetizing intraphase interaction through the hard phase and magnetic moment contribution of the soft phase. The interference region contribution was found strongly correlates with irreversible magnetic moment contribution of the soft and hard phases.

Experimental realization of analytically predicted behavior for nanoscale magnetic systems can pave the way for promoting synergistic research and has significant importance for applications and thorough understanding of nanomagnetism. Here, we report on the magnetism of a nearly ideal nanowire (NW) system, vertically aligned hcp-Co(001) single-crystal NWs electrochemically deposited inside an aluminum oxide template, as a function of the angle (0° ≤ θ ≤ 90°) between the magnetic field and the NW axis. Using high resolution transmission electron microscopy, detailed structural investigations on the few micrometers long and approximately 45 nm in diameter NWs exhibit crystalline inhomogeneities at the NW ends, evidencing magnetic localization in the single crystalline NWs. Using a vibrating sample magnetometer enabled us to extract different magnetic parameters, thereby evaluating angular dependence of magnetism in NW arrays and individual NWs. While the conventional hysteresis and first-order reversal curve (FORC) diagram methods show a monotonic decreasing and increasing behavior for coercivity as a function of θ, respectively, the average coercivity obtained from the irreversible distribution indicates a non-monotonic behavior, involving a complex magnetization reversal triggered by the propagation of vortex domain walls (DWs) and single vortex states for high field angles. Additionally, the hysteresis curve coercivity is phenomenologically parameterized at each θ based on the angular FORC (AFORC) measurements. Comparing the AFORC coercivities (varying between 5 kOe at θ = 0° and 9.3 kOe at θ = 90°) with absolute values of the angular dependence of the vortex nucleation field confirms an almost complete concurrence between experimental findings and analytical calculations on individual NWs. Consequently, our results show the first analytically supported evidence on capturing the nucleation fields and the occurrence of vortex DW propagation at each θ for weakly interacting Co NW arrays with a large magnetocrystalline anisotropy along the length.

In this study, we aim to report the role of Cu additive in arrays of pulse-electrodeposited Co nanowires (NWs) with diameters from 30 to 75 nm, embedded in porous aluminum oxide templates. This features the role of Cu additive in composition and crystalline characteristics as well as in the magnetic properties of Co NWs. Increasing the duration of off-time between pulses during the electrodeposition of Co NWs made it possible to increase the amount of Cu content, so that Co-rich CoCu NWs were obtained. The parallel coercivity and squareness values increased up to 1500 Oe and 0.8 for 30 nm diameter Co 94 Cu 6 NWs, starting from 500 Oe and 0.3 for pure Co NWs. On the other hand, although there was a substantial difference between the crystalline characteristics of 75 nm diameter pure Co and CoCu NWs, no considerable change in their magnetic properties was observed using hysteresis loop measurements. In this respect, the first-order reversal curve (FORC) analysis revealed strong inter-wire magnetostatic interactions for the CoCu NWs. Moreover, we studied the effect of thermal annealing, which resulted in an increase in the coercivity of CoCu NWs with different diameters up to 15%. As a result, the addition of small amount of Cu provides an alternative approach to tailoring the magnetic properties of Co NWs.

The emergence of novel effects such as giant magnetoresistance and magnetothermopower in single nanowires (NWs) and multilayered NWs (MNWs) makes it necessary to comprehensively understand and distinguish between their magnetic behavior and subtle characteristics. Herein, experimental fine-tuning of both ferromagnetic and non-magnetic segment thicknesses in 50 nm diameter FeNi/Cu MNW arrays from TFeNi = 25–260 nm and TCu = 2–23 nm, respectively, enables us to find the threshold TCu, below which the coercive field behavior of rod-like MNW systems magnetically saturated parallel to their long axis shows a continuous decreasing trend, which is similar to that of single NWs with integrated structure. This is in turn accompanied with enhanced magnetizing- and demagnetizing-type interactions as evidenced by first-order reversal curve (FORC) analysis. FORC measurements of disk-shaped to rod-like FeNi segments also indicate a transition from dipolar to monopolar interaction regime which coincides with continuous increasing and decreasing trends of the parallel coercivity and magnetization reversibility, being in agreement with typical MNW magnetic characteristics. Our results on the variation behavior of interaction field distribution as a function of TCu allows for evaluating the credibility of the theoretical approach proposed in the literature on the interaction field, providing threshold conditions based on the segment aspect ratio of MNW arrays.

Giant magneto-impedance (GMI) investigations comprising ZnO thin layers have received considerable attention for sensitive sensor applications. Herein, a ZnO thin layer with different thicknesses (92–503 nm) was deposited on surface of Fe-based amorphous ribbon (FeCoSiB) using RF magnetron sputtering. The GMI response and magnetic field sensitivity were investigated. While GMI% increased continuously up to the thickness of 223 nm, further increasing the ZnO thin layer thickness decreased GMI response. The GMI response and magnetic field sensitivity increased from 156% and 1.21%/Oe to 237% and 2.91%/Oe for bare Fe-based ribbon and ZnO thin layer/Fe-based ribbon/ZnO thin layer sandwich structure (223 nm in thickness), respectively. X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to characterize ZnO-enhanced structural parameters. A vibrating sample magnetometer (VSM) was used to indicate the role of the ZnO thin layer in the GMI response. Similar increasing and decreasing trends of GMI% as a function of thickness were observed in transverse permeability of samples as determined by VSM. Our results provide a simple approach to achieve high GMI response and magnetic field sensitivity by using a dielectric sandwich structure.

CoFeCu nanowires were deposited by pulsed electrodeposition technique into the porous alumina templates by a two-step mild anodization technique, using the single-bath method. The electrodeposition was performed in a constant electrolyte while Cu constant was controlled by electrodeposition current. The electrodeposition current was 3.5, 4.25, 5 and 6 mA. The effect of electrodeposition current and annealing on the magnetic behavior of the nanowires was investigated. Nanowires were fabricated with 30nm diameter and 100nm inter-pore distance with both bcc-CoFe and fcc- Cu phases. With increasing the electrodeposition current the Cu content decrease and the coercivity and magnetization increase up to its optimum value, then decrease. Annealing improved the coercivity, maximum coercivity was obtained for sample fabricated at 5 mA current. After annealing the magnetization decrease for all sampls. The X-ray diffraction pattern of the sample at electrodeposition current 3.5 mA after annealed indicates that Cu and CoFe phases separately was formed and separate peak related to CoFeCu alloy structure is not seen.

Magnetic nanowires (NWs) electrodeposited into solid templates are of high interest due to their tunable properties which are required for magnetic recording media and spintronic devices. Here, highly ordered arrays of FeNi NWs with varied lengths (ranging from 2.5 to 12 μ m) and diameters (between 45 and 75 nm) were fabricated into anodic aluminum oxide templates using a pulsed ac electrodeposition technique. X-ray diffraction patterns along with energy dispersive spectroscopy indicated the formation of Fe 70 Ni 30 NWs with fcc and bcc alloy phases, being highly textured along the bcc [110] direction. Magnetic properties were studied by hysteresis loop measurements at room temperature and they showed reductions in coercivity and squareness values by increasing length and diameter. Further, magnetic fingerprints of the NWs were characterized using the first-order reversal curve (FORC) analysis. FORC measurements revealed that, with increasing length and diameter from 2.5 to 10 μ m and 45–55 nm, respectively, besides an increase in inter-wire magnetostatic interactions, a transition from a single domain (SD) state to a pseudo SD state occurred. Moreover, a multi-domain (MD) state was found for the longest length and diameter. While the irreversible magnetization component of the SD NWs was approximately 100%, the reversible component of MD NWs increased up to 20%.

Ordered Co nanowire arrays with a constant geometry (∼40 nm diameter, ∼10 μm length and ∼100 nm interwire distance) were ac pulse electrodeposited into anodic aluminum oxide template under different deposition current densities (5.31, 7.08 and 8.85 mA/cm2). Microstructure and magnetic properties of the samples were studied using X-ray diffraction (XRD) pattern, selected area diffraction (SAED) pattern and first-order reversal curve (FORC) diagrams. SAED patterns showed inhomogeneous polycrystalline structure along the length of a nanowire. FORC diagrams revealed two-phase magnetic behavior in which soft and hard magnetic phases related to triplet cobalt crystalline directions. Despite the fact that angular dependence of hysteresis loops provides information about magnetization reversal, angular FORC offers additional information on the magnetostatic and interphase interactions depending on angle between the field and nanowires axis (α). Different magnetic behaviors were seen by change in α; interacting two-phase behavior in α = 0° which reduced to a non-interacting behavior for α > 60° may be attributed to reduce delay in magnetization reversal of two phases. Increasing the reversible portion of the major hysteresis loop in α = 90° is a possible source of difference between the hard to soft ratio obtained from FORC diagrams and XRD patterns.

CoFe/Cu multilayer nanowires were electrodeposited into anodic aluminum oxide templates prepared by a two-step mild anodization method, using the single-bath technique. Nanowires with 30 nm diameter and the definite lengths were obtained. The effect of CoFe layers thickness and annealing on the magnetic behavior of the multilayer nanowires was investigated. The layers thickness was controlled through the pulses numbers: 200, 260, 310,360 and 410 pulses were used to deposit the CoFe layers, while 300 pulse for the Cu layers. A certain increase in coercivity and squareness of CoFe/Cu multilayer nanowires observed with increasing the CoFe layer thickness and annealing improved the coercivity and decrease squareness of CoFe/Cu multilayer nanowires. First order reversal curves after annealed showed amount domains with soft magnetic phase, it also shows decreasing spreading of distribution function along the Hu axis after annealed

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 Fe47Co38Ni15 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≤22 μm, a vortex domain wall mode is only occurred. When L>22 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.

In this work, the structural, electrical and optical properties of pure and Fe doped ZnO/ZnO shell/core nanorods samples with different Fe concentrations (0–9 at.%) were studied. The samples were prepared using a two-step method; hydrothermal followed by dip coating for encapsulation process. The X-ray diffraction (XRD) results showed the Fe doping improved the crystallinity of ZnO nanorods at an optimized value (4.5 at.%). The encapsulation increased nanorods diameter by magnitude ∼20–40 nm. The structural and optical properties evidenced the Fe ions substituted with valence state 3+ into Zn2+ sites. The I–V measurements showed that resistance was increased with increase in Fe-doping due to increase carrier concentration confirmed existence of Fe ions in valance state 3+. The photoresponsivity of UV photodetectors based Fe doped ZnO nanorods demonstrated an increase trend with Fe doping.

Encapsulated ZnO nanorod arrays were fabricated using a two-step method; hydrothermal followed by dip-coating. Intensity of X-ray diffraction peaks of ZnO nanorod films increased by encapsulation with ZnO and Fe doped ZnO layer. Encapsulation process increased diameter of the rods in a range of 20–40 nm. The optical studies indicated that the band-gap decreased with increment of the nanorod diameter, and increased with Fe doping in the ZnO layer. The electrical resistance of the samples demonstrated a remarkable reduction due to encapsulation, especially in the sample encapsulated with Fe doped-ZnO layer. The photoresponse behavior of ZnO nanorod films was investigated under different powers of ultraviolet illumination. The photoresponsivity was improved for encapsulated nanorods as compared to bare nanorods.

While studying domain wall (DW) propagation in magnetic nanowires (NWs) may pave the way for future research and technological applications in recording heads and novel sensors, no attention has been paid to the investigation of magnetic reversal modes in multilayered NWs using angular first-order reversal curve (AFORC) analysis. Here, the magnetization reversal process of uniform FeNi/Cu NW arrays with a diameter of 45 nm electrodeposited in the anodic aluminum oxide template is systematically studied by AFORC analysis for the field angle θ (0° ≤ θ ≤ 90°) and compared with the average magnetic behavior of reversal modes based on conventional hysteresis loop measurements. The FeNi segment aspect ratio is kept constant at about 5, whereas the Cu segment length (LCu) increases from 2.5 to 25 nm. AFORC coercivity increases continuously with increasing θ, indicating that the NWs reverse their magnetization by nucleation and propagation of vortex DW (VDW). At θ = 0°, the respective hysteresis loop coercivity and magnetostatic coupling between FeNi segments along the NW length are reduced by increasing LCu from 2.5 to 25 nm, resulting in an enhancement in the reversible fraction of NWs from 10% to 48%. However, the VDW reversal mode is not influenced by the increase in NW reversibility as a function of θ for the different LCu, which arises from constant properties of the FeNi segments. The AFORC analysis of the reversal mechanism is also found to be in agreement with recent angle-dependent anisotropic magnetoresistance measurements in single multilayered NWs.While studying domain wall (DW) propagation in magnetic nanowires (NWs) may pave the way for future research and technological applications in recording heads and novel sensors, no attention has been paid to the investigation of magnetic reversal modes in multilayered NWs using angular first-order reversal curve (AFORC) analysis. Here, the magnetization reversal process of uniform FeNi/Cu NW arrays with a diameter of 45 nm electrodeposited in the anodic aluminum oxide template is systematically studied by AFORC analysis for the field angle θ (0° ≤ θ ≤ 90°) and compared with the average magnetic behavior of reversal modes based on conventional hysteresis loop measurements. The FeNi segment aspect ratio is kept constant at about 5, whereas the Cu segment length (LCu) increases from 2.5 to 25 nm. AFORC coercivity increases continuously with increasing θ, indicating that the NWs reverse their magnetization by nucleation and propagation of vortex DW (VDW). At θ = 0°, the respective hysteresis loop coercivity a...

Magnetic CoFe alloy nanowires were alternating current (ac)-pulse electrodeposited into the nanopores of hard anodized aluminum oxide templates. The effect of nanowires lengths on the magnetostatic interactions was investigated using first-order reversal-curve (FORC) method. FORC diagrams obtained from nanowire arrays with different lengths show drastic improvement in magnetic properties with decreasing the nanowires length. The coercivity reaches 995 Oe from initially 790 Oe. Also, the squareness enhances from 0.62 to 0.92, showing the decrease in magnetostatic interactions between the nanowires. FORC diagrams prove the decrease in magnetostatic interactions in nanowires with shorter lengths. With decreasing the nanowires length, the spread of distribution in the Hu-direction decreases. It varies from 1600 to 900 Oe when length decreases from 27 to 8 μm. FORC diagrams also reveal formation of nanowire arrays with dominant interacting single domain (SD).

Using different electrolyte compositions and varying the off-time between pulses, Co 1 x Zn x nanowire arrays were fabricated by ac pulse electrodeposition. The effect of deposition parameters on alloy contents was investigated by studying the microstructures and magnetic properties of as-deposited and annealed Co 1 x Zn x nanowires. It is shown that Zn content in CoZn nanowires exponentially increases by increasing the zinc ions in the electrolyte. The Zn content initially increases to a maximum by increase in off-time between pulses and then falls off. Adding a certain amount of Zn to Co led to form amorphous CoZn nanowires. A significant increase in magnetization, coercivity and squareness of CoZn nanowires was observed after annealing. The rate of increase in magnetization of annealed samples was seen to be inversely proportional to their initial magnetization. Improvement of magnetic properties of annealed samples may be caused by magnetic cluster formation and pinning effect.

CoCu alloy nanowire arrays were ac-pulse electrodeposited into porous anodic aluminum oxide. The effect of off-time between pulses and Cu concentration on the magnetic properties, crystalline structure and weight percentage of Co x Cu 1− x alloy nanowires have been studied by alternating gradient force magnetometer (AGFM), X-ray diffraction pattern (XRD) and energy dispersed spectrometry (EDS), respectively. Increasing the off-time between pulses decreased the weight percentage of Co in the range of ( x = 0.84 − 0.24). Results of EDS were in accordance with saturation magnetization per unit area of the samples. Coexistence of a moderate off-time and Cu concentration provided excellent conditions for fabrication of the composite nanowires which were proved by XRD patterns.

In the present work, hard anodization assisted by anode temperature ramp was employed to fabricate self-ordered nanoporous alumina in the wide range of interpore distances (259–405 nm) in pure oxalic acid and mixture of oxalic and phosphoric acid solutions. Anode temperature ramp technique was employed to adjust the anodization current density to optimize the self-ordering of the nanopore arrays in the interpore range in which no ordered self-assembled hard anodized anodic aluminum oxide has reported. It is found that the certain ratios of oxalic and phosphoric acid solutions in this anodization technique increased self-ordering of the nanopores especially for anodization voltages over the 170 V by increasing alumina’s viscous flow which could lead to decrease the overall current density of anodization, yet leveled up by anode temperature ramp. However, below 150 V anodization voltage, the ratio of interpore distance to the anodization voltage of the both anodization techniques was the same (~2 nm/V), while above this voltage, it increased to about 2.2 nm/V.

CoxFe1−x nanowire arrays with various diameters and different composition were fabricated by ac electrodeposition using porous alumina template. Coercivity along the easy axis reaches to a maximum at 2330 Oe, for CoxFe1−x nanowires containing about 40 at% Co. The crystalline structure of the nanowires was concentration-independent and shows a bcc structure. The critical diameter for transition from coherent rotation to curling mode is 35 nm for CoFe containing less than 40 at% Co while it is 30 nm for those with more than 40 at% Co. Optimizing the magnetic properties of CoFe with different Co content was seen to be dependent on the diameter of nanowires. For 25 nm diameter, the optimum was shown below 50 at% Co while it was seen above 50 at% for nanowires with 50 nm diameter. The angular dependence of the coercivity with nanowires diameter were also studied.

Humidity sensors based on nanoporous aluminum oxide are described. Accelerated mild anodization technique was employed to prepare ordered porous aluminum oxide templates in phosphoric acid electrolyte at 165 and 185 V, anodization voltages. Impedance spectroscopy was used to characterize sensitivity, response and recovery time of prepared sensors with pore diameters changing from 67 to 190 nm. Increasing the pores diameter to an optimum limit improved the sensing parameters of the prepared sensors. Sensitivity enhancement was accompanied with reduction of humidity sensing threshold to 30% RH at optimum condition. Their low response and recovery time, less than 5 and 0.5 s, respectively, categorize them as ultrafast or rapid sensors. Sensing properties is seen to reduce with reduce in aluminum purity while it improves with increase in the self ordering of alumina template. It is also found that increasing the anions percentage in the pores walls improves the sensing behavior.