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• Non-monotonic coercivity and remanence as a function of diameter for Py and Ni NTs. • Wave reversal mode could be identified by the area enclosed in the hysteresis curve. • New phase diagram allows determining the stability of the wave reversal mode. The wave reversal mode is a magnetization reversal mechanism that appears in ferromagnetic nanotubes of certain geometric parameters when an external magnetic field is applied perpendicular to their axes. The distinctive feature of this mode is that leads to well-defined S-shaped hysteresis curves. In order to gain insight into the stability of this latter effect, we have performed micromagnetic simulations for permalloy and nickel nanotubes obtaining a non-monotonic behavior for coercivity as well as for remanence as a function of nanotube diameter for both materials. Motivated on these latter intriguing results, we found that measuring the area that encloses the hysteresis curve is a novel and simple strategy to identify the appearance of the wave reversal mode. An additional contribution of this work is the proposal of a new magnetic phase diagram that allows determining the stability of this reversal mechanism as a function of the geometric and magnetic parameters of the tubes. [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]