Micro-magnetic domains are crucial for the development of next-generation non-volatile magnetic memory technologies, as they enable low-power, high-speed operation and enhanced writing endurance for data storage and logic devices. Understanding the inherent disorder within these systems is essential for studying domain dynamics, particularly when influenced by external forces. In this study, we investigate the roughness parameters, including the roughness exponent and roughness amplitude, of domain walls (DWs) in a [Co/Pd](n) multilayer within the creep regime. Our analysis reveals the evolution of DW structures as a function of Co/Pd bilayer repetition, with a transition from bubble domains to dendritic-like domains. Along with this, we reported two distinct roughness regimes in [Co/Pd](n) multilayer. We observed experimentally for [Co/Pd](n) multilayers a crossover from an effective roughness exponent with a value zeta = 0.766 at small length scales (r < 10 m) to a values close to the thermal roughness exponent, zeta = 0.521 at large length scales (r > 10 mu m), for [Co/Pd](n) multilayers which are close to theoretical predictions.

We explore the contributions of adiabatic and nonadiabatic spin-transfer torques (STT) of a spin-polarized current to the thermally activated creep motion of domain walls in a thin (Ga,Mn)(As,P) film with perpendicular anisotropy. The nonadiabatic STT is found to compensate linearly an external magnetic field, with a slope compatible with a steady domain-wall internal structure. Close to the compensation, the adiabatic contribution is strongly enhanced and may both increase or reduce domain-wall velocity, which we associate to variations of creep pinning energy barrier with domain-wall internal structure. Far from compensation, the effects of adiabatic STT become negligible and so field and current driven domain-wall motion presents common universal behaviors described by the quenched Edwards Wilkinson universality class.

In a recent publication, we showed that a monoaxial chiral magnet has a continuum of metastable helical states differing by the helix wave number. This intriguing result was obtained for the case of an infinite magnet (or a magnet with periodic boundary conditions). However, it has been pointed out that in a real magnet only one of these states is compatible with the boundary conditions, because the helix wave number is determined by the surface chiral twist. Thus, only one of the continuum of states is physically realizable. This is true for the case of a chiral magnet in contact with a nonmagnetic medium (vacuum or air, for instance), but the boundary conditions can be altered by setting the chiral magnet in contact with another magnetic medium, which may be able to absorb the surface chiral twist. We show here that this is indeed the case by studying a composite magnet system, which consists of one monoaxial chiral magnet of rectangular parallelepiped shape which has two similar slabs of a uniaxial ferromagnet attached to each of the faces that are perpendicular to the chiral axis. We show that, in the case of zero applied field, this composite system has a number of metastable helical states that are proportional to the length L0 of the chiral magnet along the chiral axis, and that the results of our previous publication are recovered in the limit L0 -> infinity.

We explore the contributions of adiabatic and non-adiabatic spin-transfer torques (STT) of a spin-polarized current to the thermally activated creep motion of domain-walls in a thin (Ga,Mn)(As,P) film with perpendicular anisotropy. For a domain-wall transverse to current, the non-adiabatic STT is found to act as an external magnetic field. Close to the compensation between these two terms, the adiabatic contribution is strongly enhanced. The domain-wall velocity may be both increased or reduced by the adiabatic STT, which we associate to variations of creep pinning energy barrier with domain-wall magnetic texture. Far from compensation, the contribution of adiabatic STT is negligible. Field and current driven domain-wall motion present common universal behaviors described by the quenched Edwards Wilkinson universality class.

We analyze the nature of the modulated magnetic states in a micromagnetic model for the monoaxial chiral magnet MnNb$_3$S$_6$ for which the Dzyaloshinskii-Moriya interaction and the dipolar interaction compete evenly. We show that the interplay between these interactions lead to a complex phase diagram including ferromagnetic states, fan-like states, in-plane stripes patterns and chiral soliton lattices. In particular, stripe patterns and chiral soliton lattices comprise non-trivial topological states with fixed chirality. The obtained phase diagram exhibits strong dependency on the thickness and on the strength of the Dzyaloshinskii-Moriya interaction. Our results can help to understand the magnetic properties of systems such as MnNb$_3$S$_6$.

At low temperature and zero applied magnetic field, besides the equilibrium helical state, monoaxial chiral helimagnets have a continuum of helical states differing by the wave number of the modulation. The wave number of these states in units of the equilibrium state wave number is denoted here by p, and accordingly the corresponding states are called the p-states. In this work we study in detail the metastability of the p-states. The application of an external magnetic field in the direction of the chiral axis has a double effect: on one hand, it introduces a conical deformation of the p-states, and on the other hand it destabilizes some of them, shrinking the range of p in which the p-states are metastable. If a polarized current is applied along the chiral axis, the p-states reach a steady moving state with a constant velocity proportional to the current intensity. Besides this dynamical effect, the polarized current also induces a conical deformation and reduces the range of stability of the p-states. The stability diagram in the plane applied field - applied current intensity has interesting features that, among other things, permit the manipulation of p-states by a combination of applied fields and currents. These features can be exploited to devise processes to switch between p-states. In particular there are p-states with negative p, opening the possibility to helicity switching. The theoretical feasibility of such processes, crucial from the point of view of applications, is shown by micromagnetic simulations. Analogous $p$-states exists in cubic chiral helimagnets and therefore similar effects are expected in those systems.

One-dimensional movement of interacting particles is a challenging problem where the correlation between particles induces non-trivial collective effects. In contrast to the single-file diffusion case, the pure ballistic single-file movement of particles has received less attention. Here, the ballistic file diffusion of hard disks is studied using an adaptative continuum Monte Carlo numerical scheme. Dynamics is studied as a function of the size of the particles, the system size and the number of particles. The mean-square displacement presents three regimes corresponding to independent motion, collective motion and finite-size effects. These regimes and the crossover times between them are analyzed and presented in analogy with the ones observed for the single-file diffusion problem.

Spin polarized currents originate a spin-transfer torque that enables the manipulation of magnetic textures. Here we theoretically study the effect of a spin-polarized current on the magnetic texture corresponding to a chiral soliton lattice in a monoaxial helimagnet under a transverse magnetic field. At sufficiently small current density the chiral soliton lattice reaches a steady motion state with a velocity proportional to the intensity of the applied current, the mobility being independent of the density of solitons and the magnetic field. This motion is accompanied with a small conical distortion of the chiral soliton lattice. At large current density the spin-transfer torque destabilizes the chiral soliton lattice, driving the system to a ferromagnetic state parallel to the magnetic field. We analyze how the deformation of the chiral soliton lattice depends on the applied current density. The destruction of the chiral soliton lattice under current could serve as a possible erasure mechanisms for spintronic applications.

Surface growth properties during irreversible multilayer deposition of straight semirigid rods on linear and square lattices have been studied by Monte Carlo simulations and analytical considerations. The filling of the lattice is carried out following a generalized random sequential adsorption mechanism where the depositing objects can be adsorbed on the surface forming multilayers. The results of our simulations show that the roughness evolves in time following two different behaviors: an "homogeneous growth regime" at initial times, where the heights of the columns homogeneously increase, and a "segmented growth regime" at long times, where the adsorbed phase is segmented in actively growing columns and inactive nongrowing sites. Under these conditions, the surface growth generated by the deposition of particles of different sizes is studied. At long times, the roughness of the systems increases linearly with time, with growth exponent β=1, at variance with a random deposition of monomers which presents a sublinear behavior (β=1/2). The linear behavior is due to the segmented growth process, as we show using a simple analytical model.

L. J. Albornoz, 2, 3 E. E. Ferrero, A. B. Kolton, 4 V. Jeudy, S. Bustingorry, and J. Curiale 3, ∗ Instituto de Nanociencia y Nanotecnoloǵıa, CNEA–CONICET, Centro Atómico Bariloche, Av. E. Bustillo 9500 (R8402AGP), San Carlos de Bariloche, Rı́o Negro, Argentina. Université Paris-Saclay, CNRS, Laboratoire de Physique des Solides, 91405, Orsay, France. Instituto Balseiro, Universidad Nacional de Cuyo–CNEA, Centro Atómico Bariloche, Av. E. Bustillo 9500 (R8402AGP) San Carlos de Bariloche, Rı́o Negro, Argentina. Centro Atómico Bariloche, Comisión Nacional de Enerǵıa Atómica (CNEA), Consejo Nacional de Investigaciones Cient́ıficas y Técnicas (CONICET), Av. E. Bustillo 9500 (R8402AGP) San Carlos de Bariloche, Rı́o Negro, Argentina. (Dated: July 19, 2021)

Self-affine rough interfaces are ubiquitous in experimental systems, and display characteristic scaling properties as a signature of the nature of disorder in their supporting medium, i.e. of the statistical features of its heterogeneities. Different methods have been used to extract roughness information from such self-affine structures, and in particular their scaling exponents and associated prefactors. Notably, for an experimental characterization of roughness features, it is of paramount importance to properly assess sample-to-sample fluctuations of roughness parameters. Here, by performing scaling analysis based on displacement correlation functions in real and reciprocal space, we compute statistical properties of the roughness parameters. As an ideal, artifact-free reference case study and particularly targeting finite-size systems, we consider three cases of numerically simulated one-dimensional interfaces: (i) elastic lines under thermal fluctuations and free of disorder, (ii) directed polymers in equilibrium with a disordered energy landscape, and (iii) elastic lines in the critical depinning state when the external applied driving force equals the depinning force set by disorder. Our results show that sample-to-sample fluctuations are rather large when measuring the roughness exponent. These fluctuations are also relevant for roughness amplitudes. Therefore a minimum of independent interface realizations (at least a few tens in our numerical simulations) should be used to guarantee sufficient statistical averaging, an issue often overlooked in experimental reports.

In monoaxial helimagnets, the Dzyaloshinskii–Moriya interaction favors inhomogeneous distributions of the magnetization with chiral modulations of solitonic character. In addition to the helical magnetic state at zero field, a chiral soliton lattice can be stabilized when a magnetic field perpendicular to the chiral axis is applied. When the magnetic field is increased, the system undergoes a phase transition to the uniform state at a critical field Bc. Above Bc, a single chiral soliton comprises the lowest level excitation over the stable uniform state, surviving as a metastable configuration. How to retain a single chiral soliton metastable state has not been addressed yet. Using micromagnetic simulations, we analyze this possibility by injecting spin polarized currents and put forward a feasible protocol to obtain a state with a single chiral soliton from the chiral soliton lattice. Our proposal could be relevant in the experimental study of metastable solitons for technological applications.

The creep motion of domain walls driven by external fields in magnetic thin films is described by universal features related to the underlying depinning transition. One key parameter in this description is the roughness exponent characterizing the growth of fluctuations of the domain wall position with its longitudinal length scale. The roughness amplitude, which gives information about the scale of fluctuations, however, has received less attention. Albeit their relevance, experimental reports of the roughness parameters, both exponent and amplitude, are scarce. We report here experimental values of the roughness parameters for different magnetic field intensities in the creep regime at room temperature for a Pt/Co/Pt thin film. The mean value of the roughness exponent is zeta = 0.74, and we show that it can be rationalized as an effective value in terms of the known universal values corresponding to the depinning and thermal cases. In addition, it is shown that the roughness amplitude presents a significant increase with decreasing field. These results contribute to the description of domain wall motion in disordered magnetic thin systems.

Understanding the effect of fabrication conditions on domain wall (DW) motion in thin films with perpendicular magnetization is a mandatory issue in order to tune their properties aiming to design spintronics devices based on such phenomenon. In this context, the present work intends to show how different growth conditions may affect DW motion in the prototypical system Pt/Co/Pt. The trilayers were deposited by dc sputtering, and the parameters varied in this study were the Co thickness, the substrate roughness and the base pressure in the deposition chamber. Magneto-optical Kerr effect-based magnetometry and microscopy combined with x-ray reflectometry, atomic force microscopy and transmission electron microscopy were adopted as experimental techniques. This permitted us to elucidate the impact on the hysteresis loops and on the DW dynamics, produced by different growth conditions. As other authors, we found that Co thickness is strongly determinant for both the coercive field and the DW velocity. On the contrary, the topographic roughness of the substrate and the base pressure of the deposition chamber evidence a selective impact on the nucleation of magnetic domains and on DW propagation, respectively, providing a tool to tune these properties.

Domain-wall dynamics and spatial fluctuations are closely related to each other and to universal features of disordered systems. Experimentally measured roughness exponents characterizing spatial fluctuations have been reported for magnetic thin films, with values generally different from those predicted by the equilibrium, depinning and thermal reference states. Here, we study the roughness of domain walls in GdFeCo thin films over a large range of magnetic field and temperature. Our analysis is performed in the framework of a model considering length-scale crossovers between the reference states, which is shown to bridge the differences between experimental results and theoretical predictions. We also quantify for the first time the size of the depinning avalanches below the depinning field at finite temperatures.

Along with experiments, numerical simulations are key to gaining insight into the underlying mechanisms governing domain wall motion in thin ferromagnetic systems. However, a direct comparison between numerical simulation of model systems and experimental results still represents a great challenge. Here, we present a tuned Ginzburg-Landau model to quantitatively study the dynamics of domain walls in quasi two-dimensional ferromagnetic systems with perpendicular magnetic anisotropy. This model incorporates material and experimental parameters and the micromagnetic prescription for thermal fluctuations, allowing us to perform material-specific simulations and at the same time recover universal features. We show that our model quantitatively reproduces previous experimental velocity-field data in the archetypal perpendicular magnetic anisotropy Pt/Co/Pt ultra-thin films in the three dynamical regimes of domain wall motion (creep, depinning and flow). In addition, we present a statistical analysis of the domain wall width parameter, showing that our model can provide detailed nano-scale information while retaining the complex behavior of a statistical disordered model.

Chiral solitons are one dimensional localized magnetic structures that are metastable in some ferromagnetic systems with Dzyaloshinskii-Moriya interactions and/or uniaxial magnetic anisotropy. Though topological textures in general provide a very interesting playground for new spintronics phenomena, how to properly create and control single chiral solitons is still unclear. We show here that chiral solitons in monoaxial helimagnets, characterized by a uniaxial Dzyaloshinskii-Moriya interaction, can be stabilized with external magnetic fields. Once created, the soliton moves steadily in response to a polarized electric current, provided the induced spin-transfer torque has a dissipative (nonadiabatic) component. The structure of the soliton depends on the applied current density in such a way that steady motion exists only if the applied current density is lower than a critical value, beyond which the soliton is no longer stable.