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In this work, we present a theoretical model for domain wall (DW) oscillations in a curved magnetic nanowire with a constant curvature under the action of a uniaxial magnetic field. Our results show that the DW dynamics can be described as that of the mechanical pendulum, and both the NW curvature and the external magnetic field influence its oscillatory frequency. A comparison between our theoretical approach and experimental data in the literature shows an excellent agreement. The results presented here can be used to design devices demanding the proper control of the DW oscillatory motion in NWs.

This work analyzes the propagation of a transverse domain wall (DW) motion under the action of an electric current along a nanowire (NW) with a curvature gradient. Our results evidence that the curvature gradient induces a chiral spin-transfer torque (CSTT) whose effect on the DW motion depends on the direction along which the DW points. The origin of the CSTT is explained in terms of a position and phase-dependent effective field associated with the DW profile and the electric current direction. Finally, our results reveal that this chiral mechanism can also affect the behavior of other magnetization collective modes, such as spin waves. This work shows the emergence of curvature-induced chiral spin transport and highlights a new phenomenon to be considered for designing spintronic devices., Comment: 7 pages, 3 figures

Through micromagnetic simulations, this work analyzes the stability of Bloch points in magnetic nanospheres and the possibility of using an array of such particles to compose a system with the features of a magnetic trap. We show that a BP can be nucleated as a metastable configuration in a relatively wide range of the nanosphere radius compared to a quasi-uniform and vortex state. We also show that the stabilized Bloch point generates a quadrupolar magnetic field outside it, from which we analyze the field profile of different arrays of these nanospheres to show that the obtained magnetic field shares the features of magnetic traps. Some of the highlights of the proposed magnetic traps rely on the magnetic field gradients achieved, which are orders of magnitude higher than standard magnetic traps, and allow three-dimensional trapping. Our results could be useful in trapping particles through the intrinsic magnetization of ferromagnetic nanoparticles while avoiding the commonly used mechanisms associated with Joule heating.

Understanding the domain wall (DW) dynamics in magnetic nanowires (NW) is crucial for spintronic-based applications demanding the use of DWs as information carriers. This work focuses on the dynamics of a DW displacing along a bent NW with an elliptical shape under the action of spin-polarized electric currents and external magnetic fields. Our results evidence that a curvature gradient induces an exchange-driven effective tangential field responsible for pinning a DW near the maximum curvature point in a NW. The DW equilibrium position depends on the competition between the torques produced by the external stimuli and the curvature-induced effective fields. When the external stimuli are below a certain threshold, the DW follows a damped harmonic oscillation around the equilibrium position. Above this threshold, DW displaces along the NW under an oscillatory translational motion.

We investigate the dynamics of two skyrmions lying in distinct layers of an antiferromagnetic bilayer system, consisting of nanostripes with the shape of racetracks. The top and bottom nanostripes are separated by a height offset and they are coupled through a ferromagnetic exchange, allowing the interaction between the skyrmions from both layers. Depending on the distance between the skyrmions they attract each other sufficiently to achieve a bound state. We also analyze their dynamics when an electric current is applied in a unique layer and we determine how the bound-state nucleation depends on the current density and vertical distance between the skyrmions. Finally, we analyzed the robustness of the bound states by considering two situations: 1) a system constituted by clean or homogeneous antiferromagnetic racetracks; 2) a system in which randomly distributed magnetic impurities in both layers are included in the system., Comment: 8 pages, 7 figures

In this work, we study the dynamic range of a neuronal network of excitable neurons with excitatory and inhibitory synapses. We obtain an analytical expression for the critical point as a function of the excitatory and inhibitory synaptic intensities. We also determine an analytical expression that gives the critical point value in which the maximal dynamic range occurs. Depending on the mean connection degree and coupl\-ing weights, the critical points can exhibit ceasing or ceaseless dynamics. However, the dynamic range is equal in both cases. We observe that the external stimulus mask some effects of self-sustained activity (ceaseless dynamic) in the region where the dynamic range is calculated. In these regions, the firing rate is the same for ceaseless dynamics and ceasing activity. Furthermore, we verify that excitatory and inhibitory inputs are approximately equal for a network with a large number of connections, showing excitatory-inhibitory balance as reported experimentally.

During the last years, topologically protected collective modes of the magnetization have called much attention. Among these, skyrmions and merons have been the object of intense study. In particular, topological skyrmions are objects with an integer skyrmion number $Q$ while merons have a half-integer skyrmion charge $q$. In this work, we consider a $Q=1$ skyrmion, composed by a meron and an antimeron (bimeron), displacing in a ferromagnetic racetrack, disputing a long-distance competition with its more famous counterpart, the typical $Q=1$ cylindrically symmetrical skyrmion. Both types of topological structures induce a Magnus force and then are subject to the Hall effect. The influence of the Dzyaloshinskii-Moriya interaction ($DMI$) present in certain materials and able to induces $DMI$-skyrmions is also analyzed. Our main aim is to compare the motions (induced by a spin-polarized current) of these objects along with their own specific racetracks. We also investigate some favorable factors which are able to give breath to the competitors, impelling them to remain in the race for longer distances before their annihilation at the racetrack lateral border. An interesting result is that the $DMI$-skyrmion loses this hypothetical race due to its larger rigidity., Comment: 6 pages, 5 figures

Curvature of nanomagnets can be used to induce chiral textures in the magnetization field. Here we perform analytical calculations and micromagnetic simulations aiming to analyze the stability of in-surface magnetization configurations in toroidal nanomagnets. We have obtained that despite toroidal vortex-like configurations are highly stable in magnetic nanotori, the interplay between geometry and magnetic properties promotes the competition between effective interactions yielding the development of a core in a vortex state when the aspect ratio between internal and external radii of nanoturus is $\gtrsim0.75$.

Magnetic nanorings have been widely studied due to their potential applications in spintronic and magnonic devices. In this work, by means of analytical calculations and micromagnetic simulations we have analyzed the magnetic energy of nanorings with variable anisotropy along their radius. Four magnetic states, including two new magnetic configurations, here called meron and knot-like states, are considered, looking to the relative lower energy states as a function of anisotropy. Phase diagrams with this states are presented., Comment: 6 pages, 4 figures

A discussion on the interaction between skyrmions in a bi-layer system connected by a non-magnetic metal is presented. From considering a free charge carrier model, we have shown that the Ruderman-Kittel-Kasuya-Yosida (RKKY ) inter- action can induce attractive or repulsive interaction between the skyrmions depending on the spacer thickness. We have also shown that due to an increasing in RKKY energy when the skyrmions are far from each other, their widths are diminished. Finally, we have obtained analytical solutions to the skyrmion position when the in-plane distance between the skyrmions is small and it is shown that an attractive RKKY interaction yields a skyrmion precessory motion. This RKKY-induced coupling could be used as a skyrmion drag mechanism to displace skyrmions in multilayers., Comment: 5 Pages, 7 Figures

Understanding the domain wall dynamics is an important issue in modern magnetism. Here we present results of domain wall displacement in curved cylindrical nanowires at a constant magnetic field. We show that the average velocity of a transverse domain wall increases with curvature. Contrary to what it is observed in stripes, in a curved wire the transverse domain wall oscillates along and rotates around the nanowire with the same frequency. These results open the possibility of new oscillation-based applications., Comment: 6 Figures