http://hdl.handle.net/10366/138184 Tue, 21 Apr 2026 17:31:26 GMT 2026-04-21T17:31:26Z http://hdl.handle.net/10366/170810 [EN]The usefulness of modeling magnetocaloric materials expands from the understanding of their behavior to the prediction of new materials, playing a fundamental role in the optimization of their performance. In contrast with other areas of magnetic materials research, micromagnetic simulations of magnetocaloric materials are scarce due to the difficulty of modeling the material in the vicinity of the transition. To solve this limitation, we propose to use the Landau–Lifshitz–Bloch micromagnetic simulations to study the magnetocaloric effect associated with a second-order ferromagnetic↔paramagnetic transition. Following our proposed methodology and considering material parameters in a mean-field framework, we obtain reliable isothermal entropy change curves for monocrystalline and polycrystalline configurations, where we consider different anisotropic contributions. The robustness of the method was evaluated, yielding results that agreed with previous experimental and theoretical observations. Our study shows that micromagnetic simulations are a powerful tool for analyzing second-order magnetocaloric materials with complex microstructures. Thu, 01 Jan 2026 00:00:00 GMT http://hdl.handle.net/10366/170810 2026-01-01T00:00:00Z http://hdl.handle.net/10366/169335 [EN]Surface Acoustic Waves (SAW) have been used in spintronic applications to decrease the magnetic field or the electric current required to act on the magnetization. A common belief is that a SAW alone cannot achieve a directed magnetic switching in a device without an assisting magnetic field or electric current. In this work, we demonstrate magnetic domain wall motion driven solely by an acoustic wave. Using XMCD-PEEM, we show extensive evidence of SAW-induced and field-free magnetic domain wall motion (DW) in the direction of the wave propagation. Our micromagnetic simulations reveal a mechanism that allows the SAW to transfer linear momentum to the DW. Experimentally, the largest DW average velocity measured was ~12m/s, although our simulations predict that velocities in the range of 100 m/s could be attained. This new mechanism opens the door to designing innovative spintronic devices where the magnetization can be controlled exclusively by an acoustic wave. Wed, 01 Jan 2025 00:00:00 GMT http://hdl.handle.net/10366/169335 2025-01-01T00:00:00Z http://hdl.handle.net/10366/169334 [EN]The dynamics of achiral Néel domain walls (DWs) driven by spin-orbit torque in wide ferromagnetic strips is investigated. The study reveals that these DWs cease motion above a certain threshold current density, while their internal magnetic moments exhibit a spatial modulation characterized by a 180∘ rotation leading to a quasi-sinusoidal distortion of their shape. Unlike achiral DWs in narrow strips, which stop because they take on a Bloch configuration, achiral DWs in wide strips stop due to the internal diffusive torques originating from exchange interaction that counterbalance locally the torques contributing to the DW dynamics. If these torques are perfectly balanced, the DW remains stationary, whereas the slighter imbalance triggers complex nonlinear dynamics, including continuous oscillation of the domain wall magnetization or quasi-periodic explosions in which the domain wall “cracks" and recovers its structure afterwards. Our findings unveil a dissipative solitonic signature in achiral domain walls driven by SOT, akin to dissipative solitons observed in other scientific fields. This work paves the way for exploring nonlinear spatio-temporal dynamics in DWs with potential applications in logic and neuromorphic computing. Wed, 01 Jan 2025 00:00:00 GMT http://hdl.handle.net/10366/169334 2025-01-01T00:00:00Z http://hdl.handle.net/10366/169299 [EN]This review describes recent advances in spintronics that have the potential to impact key areas of information technology and microelectronics. Four main axes of research are identified: nonvolatile memories, magnetic sensors, microwave devices, and beyond-CMOS logic. We discuss state-of-the-art developments in these areas as well as opportunities and challenges that will have to be met, both at the device and system level, in order to integrate novel spintronic functionalities and materials in mainstream microelectronic platforms. Wed, 01 Jan 2020 00:00:00 GMT http://hdl.handle.net/10366/169299 2020-01-01T00:00:00Z http://hdl.handle.net/10366/168112 [EN]Single-shot all-optical helicity independent switching processes are investigated using advanced micromagnetic modeling in a ferrimagnetic thin film embedded in a multilayer stack. Building on recent experimental findings, our multiscale simulations realistically account for heat transport in the stack, focusing on the influence of a metallic copper underlayer with varying thickness. We analyze how this thermal transport affects the final magnetic state of the ferrimagnet as a function of both the laser pulse duration and fluence. Our results reproduce the experimentally observed switching behaviors and elucidate the physical mechanisms that govern the emergence of three distinct final magnetic states. In particular, we demonstrate how these states are critically influenced by the thickness of the underlying copper layer. Wed, 01 Jan 2025 00:00:00 GMT http://hdl.handle.net/10366/168112 2025-01-01T00:00:00Z http://hdl.handle.net/10366/167888 [EN]Domain-wall (DW) devices have garnered recent interest for diverse applications including memory, logic, and neuromorphic primitives; fast and accurate device models are therefore imperative for the design and verification of large-scale systems. Existing models of DW motion are suboptimal for the design of large-scale systems as they either overconsume compute resources with physics-heavy equations or oversimplify the physics, drastically reducing model accuracy. We propose a DW model inspired by the phenomenological similarities between themotions of a DWand a classical object being acted on by forces such as air resistance and static friction. Our proposed phenomenological model predicts DW motion within 1.1% on average and is 4000 times faster than micromagnetic simulations. In addition, our model is seven times faster than existing collective-coordinate models and 14 times more accurate than existing hyper-reduced models, making it an essential tool for large-scale DW circuit design and simulation. The model is publicly available, along with scripts that can automatically extract model parameters from userprovided simulation or experimental data, allowing the user to extend the model to a wider range of micromagnetic parameters. Wed, 01 Jan 2025 00:00:00 GMT http://hdl.handle.net/10366/167888 2025-01-01T00:00:00Z http://hdl.handle.net/10366/167041 [EN]Antiferromagnetic magnonics has become the focus of intense scientific research because of the advantages of these materials compared to ferromagnets. However, ferrimagnetic materials have received much less attention despite exhibiting similar dynamical features at the angular momentum compensation point. In this paper, we present analytical expressions describing the dispersion relation of forward volume spin waves in ferrimagnetic materials near the angular momentum compensation point. We benchmark the derived dispersion relations against full micromagnetic simulations showing an excellent agreement between both approaches. We predict two different branches for forward volume spin waves in ferrimagnetic materials merging into a single branch at the angular momentum compensation point. Our results can assist in the design of magnonic devices built on ferrimagnetic materials. Wed, 01 Jan 2025 00:00:00 GMT http://hdl.handle.net/10366/167041 2025-01-01T00:00:00Z http://hdl.handle.net/10366/165885 [EN]Disorder in ultrathin magnetic films can significantly hinder domain-wall motion. One of the main issues on the path toward efficient domain-wall-based devices remains the characterization of the pinning landscape at the nanoscale. In this paper, we study domain-wall motion in W/Co-Fe-B/MgO thin films with perpendicular magnetic anisotropy crystallized by annealing at 400⁢∘⁢C and a process based on He+ irradiation combined with moderated temperatures. The magnetic properties are similar for the whole series of samples, while the magnetic domain-wall mobility is critically improved in the irradiated samples. By using an analytical model to extract the nanoscale pinning parameters, we reveal important variations in the disorder of the crystallized samples. This work offers an opportunity to selectively analyze the effects of disorder on the domain-wall dynamics, without the contribution of changes in the magnetic properties. Our results highlight the importance of evaluating the nanoscale pinning parameters of the material when designing devices based on domain-wall motion, which in return can be a powerful tool to probe the disorder in ultrathin magnetic films. Sat, 01 Jan 2022 00:00:00 GMT http://hdl.handle.net/10366/165885 2022-01-01T00:00:00Z http://hdl.handle.net/10366/165858 [EN]Toggle spin-orbit torque (SOT)-driven magnetoresistive random access memory (MRAM) with perpendicular anisotropy has a simple material stack and is more robust than directional SOT-MRAM. However, a read-before-write operation is required to use the toggle SOT-MRAM for directional switching, which threatens to increase the write delay. To resolve these issues, we propose a high-speed memory architecture for toggle SOT-MRAM that includes a minimum-sized bit cell and a custom read-write driver. The proposed driver induces an analog self-terminating SOT current that functions via an analog feedback mechanism that can read and write the toggle SOT-MRAM bit cell within a single clock cycle. As the read and write operations are completed within 570 ps, this memory architecture provides the first viable solution for nonvolatile L3 cache. Wed, 01 Jan 2025 00:00:00 GMT http://hdl.handle.net/10366/165858 2025-01-01T00:00:00Z http://hdl.handle.net/10366/165855 [EN]The interfacial Dzyaloshinskii–Moriya interaction (DMI) can be exploited in magnetic thin films to realize lateral chirally coupled systems, providing a way to couple different sections of a magnetic racetrack and realize interconnected networks of magnetic logic gates. Here, we systematically investigate the interplay between spin–orbit torques, chiral coupling, and the device design in domain wall racetracks. We show that the current-induced domain nucleation process can be tuned between single-domain nucleation and repeated nucleation of alternate domains by changing the orientation of an in-plane patterned magnetic region within an out-of-plane magnetic racetrack. Furthermore, by combining experiments and micromagnetic simulations, we show that the combination of damping-like and field-like spin–orbit torques with DMIresults in selective domain wall injection in one of two arms of a Y-shaped device depending on the current density. Such an element constitutes the basis of domain wall based demultiplexer, which is essential for distributing a single input to any one of the multiple outputs in logic circuits. Our results provide input for the design of reliable and multifunctional domain wall circuits based on chirally coupled interfaces. Mon, 01 Jan 2024 00:00:00 GMT http://hdl.handle.net/10366/165855 2024-01-01T00:00:00Z http://hdl.handle.net/10366/165854 [EN] Nucleation of domain walls by current-driving a single domain wall, confined to the junction area of two symmetrical strips, is investigated using systematic micromagnetic simulations. Secondary domain walls (equivalently, bits encoded in domains) are simultaneously nucleated and driven by alternatively applying current pulses between two terminals in the structure. Simulations show that nanosecond-duration current pulses nucleate and drive series of robust up/down domains even under realistic conditions. These results demonstrate a technique for sequentially nucleating and shifting domain walls without using attached external “bit lines,” fields, or modifying the ferromagnetic strip. Sat, 01 Jan 2022 00:00:00 GMT http://hdl.handle.net/10366/165854 2022-01-01T00:00:00Z http://hdl.handle.net/10366/165853 [EN]Micromagnetic simulations are used to investigate the effect of an external magnetic field on the interaction between domain walls and linearly polarized propagating spin waves in synthetic antiferromagnets. Two regimes with a sharp transition between them are found. At large fields, spin waves are strongly reflected by the domain wall and, consequently, the latter is propelled forward. At low fields, however, there is no reflection and yet the domain wall undergoes a small forward displacement, which is attributed to the change in linear momentum of the magnons as they pass through the domain wall and to the imbalance in the population of the two oscillation modes present in the linearly polarized excitation. The transition between the two regimes occurs at the field value for which the excitation frequency falls below the threshold of the high-frequency mode. Mon, 01 Jan 2024 00:00:00 GMT http://hdl.handle.net/10366/165853 2024-01-01T00:00:00Z http://hdl.handle.net/10366/165852 [EN]The response of a magnetic domain wall to an external magnetic field in a perpendicularly magnetized synthetic antiferromagnet is studied using both micromagnetic simulations and a reduced model. It is found that the external field induces a sizable displacement between the position of the domain wall in each layer, which can be larger than the domain wall width for a sufficiently strong field. We also study the dynamic evolution of the system when this field is applied or removed. In both cases we find a complex response with two distinct phases that involve both internal domain wall rotation and coupled interlayer domain wall oscillations. As a result of this dynamics spin waves are radiated. The emitted radiation is characterized by a broadband spectrum and can be detected far away from the domain wall. Mon, 01 Jan 2024 00:00:00 GMT http://hdl.handle.net/10366/165852 2024-01-01T00:00:00Z http://hdl.handle.net/10366/165827 [EN]Ultrafast laser pulses provide unique tools to manipulate magnetization dynamics at femtosecond timescales, where the interaction of the electric field usually dominates over the magnetic field. Recent proposals using structured laser beams have demonstrated the possibility to produce regions where intense oscillating magnetic fields are isolated from the electric field. In these conditions, we show that technologically feasible Tesla-scale circularly polarized high-frequency magnetic fields induce purely precessional nonlinear magnetization dynamics. This fundamental result not only opens an avenue in the study of laser-induced ultrafast magnetization dynamics, but also sustains technological implications as a route to promote all-optical non-thermal magnetization dynamics both at shorter timescales—towards the subfemtosecond regime— and at THz frequencies Mon, 01 Jan 2024 00:00:00 GMT http://hdl.handle.net/10366/165827 2024-01-01T00:00:00Z http://hdl.handle.net/10366/165381 [EN]In this work, we test the thermal rupture of a permalloy strip when an electric current is flowing through the strip. For a strip with the top surface exposed to air or covered with a thin insulating layer, we find that the strip gets destroyed at a DC density of only 0.6x10^12 A/m2^ and a temperature smaller than 400 K, while it can withstand 1.5x10^12 A/m2 and 1200K if the current is delivered in a sub-ls pulse. If the permalloy strip is covered with a heat dissipation window of Ta2O3/Pt or Ta2O3/Au, so the permalloy can also conduct heat through the top surface, the strip can withstand 3.5x10^12 A/m2 and 2000 K. Interestingly, the strips always break in a section not covered by the dissipation window, even if that is not the hottest part of the strip. Therefore, the layers forming the dissipation window help with not only extracting the heat but also delaying the structural damage. Sun, 01 Jan 2023 00:00:00 GMT http://hdl.handle.net/10366/165381 2023-01-01T00:00:00Z http://hdl.handle.net/10366/163184 [EN]Computational reversibility is necessary for quantum computation and inspires the development of computing systems, in which information carriers are conserved as they flow through a circuit. While conservative logic provides an exciting vision for reversible computing with no energy dissipation, the large dimensions of information carriers in previous realizations detract from the system efficiency, and nanoscale conservative logic remains elusive. We therefore propose a nonvolatile reversible computing system in which the information carriers are magnetic skyrmions, topologically-stable magnetic whirls. These nanoscale quasiparticles interact with one another via the spin Hall and skyrmion Hall effects as they propagate through ferromagnetic nanowires structured to form cascaded conservative logic gates. These logic gates can be directly cascaded in large-scale systems that perform complex logic functions, with signal integrity provided by clocked synchronization structures. The feasibility of the proposed system is demonstrated through micromagnetic simulations of Boolean logic gates, a Fredkin gate, and a cascaded full adder. As skyrmions can be transported in a pipelined and nonvolatile manner at room temperature without the motion of any physical particles, this skyrmion logic system has the potential to deliver scalable high-speed low-power reversible Boolean and quantum computing. Tue, 01 Jan 2019 00:00:00 GMT http://hdl.handle.net/10366/163184 2019-01-01T00:00:00Z