Search

In this study, we investigate the pseudo-static magnetic properties of Permalloy conical frustum nanowires using micromagnetic simulations. We thoroughly examine how both the major and minor radii influence the magnetic reversal mechanism when an external magnetic field is applied parallel to the nanowire axis. The obtained results show that under specific geometrical conditions, magnetization reverts though a Bloch point-type domain wall. In these cases, hysteresis curves exhibit two Barkhausen jumps during magnetization reversal, forming a plateau field range in which a Bloch point domain wall nucleates and propagates until its annihilation after the second Barkhausen jump. The nucleation of a Bloch point domain wall in a frustum conical nanowire geometry is reported. These findings highlight the significance of this geometry in nucleating these attractive topological defects for promising applications. [ABSTRACT FROM AUTHOR]

In this study, we investigate the magnetic properties of interconnected permalloy nanowire networks using micromagnetic simulations. The effects of interconnectivity on the hysteresis curves, coercivity, and remanence of the nanowire networks are analyzed. Our results reveal intriguing characteristics of the hysteresis curves, including nonmonotonic behaviors of coercivity as a function of the position of horizontal nanowires relative to vertical nanowires. By introducing horizontal nanowires at specific positions, the coercivity of the nanowire networks can be enhanced without altering the material composition. The normalized remanence remains relatively constant regardless of the position of the horizontal wires, although it is lower in the interconnected nanowire arrays compared to nonconnected arrays. These findings provide valuable insights into the design and optimization of nanowire networks for applications requiring tailored magnetic properties. [ABSTRACT FROM AUTHOR]

In this paper, our objective was to investigate the static and dynamic magnetic properties of Fe3O4 nanotubes that are 1000 nm long, by varying the external radius and the thickness of the tube wall. We performed a detailed numerical analysis by simulating hysteresis curves with an external magnetic field applied parallel to the axis of the tubes (along the z-axis). Our findings indicate that nanotubes with an external radius of 30 nm exhibit non-monotonic behavior in their coercivity due to a change in the magnetization reversal mechanism, which was not observed in nanotubes with external radii of 80 nm. Additionally, we explored the dynamic susceptibility of these nanotubes and found that the position and number of resonance peaks can be controlled by manipulating the nanotube geometry. Overall, our study provides valuable insights into the behavior of Fe3O4 nanotubes, which can aid in the design and improvement in pseudo-one-dimensional technological devices. [ABSTRACT FROM AUTHOR]

Anodic alumina membranes with modulated pore diameters serve as template for the preparation of magnetic nanowires. Filling the pores with Ni by electrodeposition delivers wires replicating the variation in modulation in pore diameter from 80 to 160 nm. Such structures are of interest for the observation and control of magnetic domain wall motion. Single-object characterization utilizing the magneto-optical Kerr effect magnetometry evidences a strong correlation between geometric parameters and magnetic properties. Ensemble magnetization measurements with a superconducting quantum interference device show the effect of dipolar interactions. Analytical models can reproduce the lowering of coercivity due to the presence of enhanced stray fields within the array. Magnetic force microscopy at individual wires indicates the presence of a strong stray field in the vicinity of the diameter change. The preparation technique demonstrates a mass production method of nano-objects with designed geometric irregularities, which could be used to control the motions of magnetic domain walls. [ABSTRACT FROM AUTHOR]

Ordered arrays of magnetic nanotubes are prepared by combining a porous template (anodic alumina) with a self-limiting gas-solid chemical reaction (atomic layer deposition). The geometric parameters can thus be tuned accurately (tube length of 1–50 μm, diameter of 20–150 nm, and wall thickness of 1–40 nm), which enables one to systematically study how confinement and anisotropy effects affect the magnetic properties. In particular, the wall thickness of such ordered Fe3O4 nanotubes has a nonmonotonic influence on their coercive field. Theoretical models reproduce the size effects that are experimentally observed and interpret them as originating from a crossover between two distinct modes of magnetization reversal. [ABSTRACT FROM AUTHOR]

• Wire-tube nanostructures. • Hysteresis loops. • Barkhausen jumps. We have studied the magnetostatic interactions between two parallel cylindrical nanostructures with wire-tube morphology as a function of their interaxial separation and the magnetic field applied using micromagnetic simulations. We find that the hysteresis curves of the system can exhibit one, two or three Barkhausen jumps as a function of the separation between the nanostructures and the angle at which the external magnetic field is applied, which are related to the reversal of the magnetic moments of certain segments of the nanostructures. In addition, by studying the averages of magnetization we obtain that for angles less than or equal to 60 degrees, the nanostructures reverse their magnetization through the nucleation and propagation of domain walls (vortex for the tube segment and transverse for the wire segment), while for higher angles the nanostructures revert their magnetization by quasi-coherent rotation. [ABSTRACT FROM AUTHOR]

Ni 81 Fe 19 O y thin films with different thicknesses were obtained by atomic layer deposition. After a thermal reduction process, Ni 81 Fe 19 O y films were converted to their strong Ni 81 Fe 19 ferromagnetic phase, usually known as Permalloy. The different thicknesses were obtained by considering 500, 1000, 1500 and 2000 supercycles, which are defined as a cycle of NiCp 2 /O 3 followed by another cycle of FeCp 2 /O 3 . The samples were characterized before and after the thermal reduction process with respect to their crystallinity, morphology and magnetism. In particular, the thermally reduced samples exhibit holes whose sizes increase significantly as the thickness of the samples also increases, affecting their magnetic behaviour. As Permalloy is widely used in many applications, its synthesis through atomic layer deposition is expected to introduce comparative advantages over other synthesis processes, opening up new possibilities for nanoelectronic devices. [ABSTRACT FROM AUTHOR]

Nickel oxide thin films with different thicknesses were synthesized by atomic layer deposition. After a thermal reduction process, under a controlled atmosphere of hydrogen, it was possible to convert nickel oxide to metallic nickel. The different thicknesses were obtained for 250 to 2000 cycles of NiCp 2 /O 3 . The Ni thin films were characterized by X-ray diffraction, scanning electron microscopy, and by Magneto-Optical Kerr effect measurements. Micromagnetic simulations have been performed to investigate the mechanism of magnetization reversion of these films. Interestingly, the thermal reduction of films synthesized by ALD allows the generation of both randomly oriented, sized and spaced Ni islands and antidot arrays from thin films. [ABSTRACT FROM AUTHOR]

• Fe 2 O 3 thin films can be obtained at 200 °C by atomic layer deposition. • Fe 2 O 3 films can be reduced to Fe 3 O 4 films by annealing in H 2 /Ar at 400 °C. • Different thicknesses were obtained considering from 500 to 2000 cycles of FeCp 2 /O 3. • Controlling the thickness of Fe 3 O 4 films allows adjusting their magnetic properties. Hematite (α-Fe 2 O 3) thin films with different thicknesses between 4 and 16 nm were synthesized by atomic layer deposition, employing 500 to 2000 cycles of FeCp 2 /O 3. After a thermal reduction process, under a controlled atmosphere of hydrogen, it was possible to convert hematite to magnetite (Fe 3 O 4). SEM images of the iron oxide thin films showed that they are macroscopically homogeneous, although the magnetic measurements by MOKE indicated that the samples should present holes that are responsible for pinning the domain walls, raising the coercivity to values ​​that vary between 0.3 and 0.7 kOe. XRD revealed the presence of the Fe 3 O 4 phase by identifying the main peaks. The signal obtained by Raman spectroscopy was identified at 667 cm−1, which suggests the presence of the phonon mode A1g of Fe 3 O 4 in the reduced sample. Controlling the thickness of Fe 3 O 4 thin films allows adjusting their magnetic properties, coercivity and remanence, so that they can be used in potential technological applications. [ABSTRACT FROM AUTHOR]

• Permalloy nanowires of 30 nm in diameter and 1 μm in length obtained by AC electrodeposition. • Coercivity and remanence decrease with increasing angles at which the external field is applied. • Magnetostatic interaction modifies the shape of hysteresis curves of simulated Py NW arrays. • Py NW arrays reverse magnetization by nucleation and propagation of transverse domain walls. • Jumps in magnetization observable in hysteresis curves are proportional to the number of simulated Py NWs. This work contributes to the understanding of angular dependence of the magnetic properties of Permalloy nanowire arrays by means of a comparative analysis between experiment and micromagnetic simulations. On the one hand, Permalloy nanowires of 30 nm in diameter and 1 μm in length were synthesized by AC electrodeposition inside mesoporous alumina templates. Magnetic experimental measurements show that both coercivity and remanence decrease monotonously as the angle, at which the external field is applied, increases. On the other hand, the comparison between the simulation of a nanowire array and that performed for one single nanowire reveals that the magnetostatic interactions between the nanowires strongly modifies not only the shape of the hysteresis curve but also the coercivity and remanence values. Besides, simulations also disclose that the nanowires reverse their magnetization through the nucleation and propagation of transverse domain walls. Moreover, the simulation of an array of nanowires also discloses that the hysteresis curve exhibits noticeable jumps in the magnetization that are proportional to the number of nanowires that reverse their magnetization in the array. This latter could provide an interesting hint to control the performance of magnetic nanodevices. [ABSTRACT FROM AUTHOR]

• We have performed micromagnetic simulations of Ni and Py nanotubes as a function of the external magnetic field. • A new striking reversal mechanism, which we have called wave reversal mode (W), has been identified. • This phenomenon describes unusual behaviors in nanotubes when the field is applied perpendicular to its axis. • A sharp increase in remanence is an unequivocal signal that the system reverses according to this mechanism. We have investigated the magnetic properties of 14 nm thick and 1 μm long nickel and permalloy nanotubes with external diameters of 40 and 100 nm as a function of the angle θ at which the external magnetic field is applied. Our results show that the coercivity of 40 nm diameter nickel nanotubes follows a non-monotonic behavior from θ = 0° up to θ = 60°, while that corresponding to permalloy displays an increasing monotonic trend at the same angular range. At θ = 90°, both materials evidence a sharp drop of the coercivity to zero, indicating that the reversal mechanism has changed to a pseudo-coherent rotation. On the other hand, nickel and permalloy nanotubes with 100 nm in diameter exhibit a similar angular dependence of the coercivity, reversing their magnetization through the nucleation and propagation of vortex domain walls for angles lower than 75°. For θ = 90°, a novel striking mechanism, the wave reversal mode (W), arises. This phenomenon leads to an unusual S-type shape in the hysteresis curves at those given parameters, which is until now an effect that has not been reported for these nanostructures. [ABSTRACT FROM AUTHOR]