Skyrmions are topologically protected field configurations with particle-like properties that play important roles in various fields of science. Recently, skyrmions have been directly observed in chiral magnets. Here, we investigate the effects of nonmagnetic impurities (structural point-like defects) on the different initial states (random or helical states) and on the formation of the skyrmion crystal in a discrete lattice. By using first-principle calculations and Monte Carlo techniques, we have shown that even a small percentage of spin vacancies present in the chiral magnetic thin film affects considerably the skyrmion order. The main effects of impurities are somewhat similar to thermal effects. The presence of these spin vacancies also induces the formation of compact merons (bimerons) in both the helical and skyrmion states. We have also investigated the effects of adjacent impurities producing only one hole (with an almost circular shape) intentionally inserted into the plate (forming a non-simply connected manifold) on the skyrmion crystal.
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.
Topological stability of skyrmions is an important element for using these objects in new technologies such as skyrmionics, spintronics and so on. Indeed, this kind of stability keeps the skyrmion structure unbending, shielding the information that, by chance, it could carry. On the other hand, a controlled manipulation of the skyrmion configuration could be an extra ingredient for technological applications. It is not an easy task and particularly, the control of skyrmion polarity and chirality (for Block-type), and helicity (for Néel-type) may be important in this direction. Here, we have investigated the skyrmion oscillatory motion in a hybrid nanodisk by using atomistic spin dynamics simulations. If a skyrmion is put to oscillate in a disk formed by two different materials, having opposite Dzyaloshinskii-Moriya interactions ($D_{1}=-D_{2}$), then, its helicity experiences an inversion. Nonetheless, if the skyrmion oscillations occur in a homogeneous disk submitted to opposites magnetic fields in distinct regions (for instance, semi-disks $1$ and $2$), the skyrmion polarity and helicity suffer an inversion. Such skyrmionic-oscillators could provide a dynamical degree of freedom, yielding new functionalities to skyrmion-based logic devices.
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