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Register a new userHysteresis of nanocylinders with Dzyaloshinskii-Moriya interaction
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The potential for application of magnetic skyrmions in high density storage devices provides a strong drive to investigate and exploit their stability and manipulability. Through a three-dimensional micromagnetic hysteresis study, we investigate the question of existence of skyrmions in cylindrical nanostructures of variable thickness. We quantify the applied field and thickness dependence of skyrmion states, and show that these states can be accessed through relevant practical hysteresis loop measurement protocols. As skyrmionic states have yet to be observed experimentally in confined helimagnetic geometries, our work opens prospects for developing viable hysteresis process-based methodologies to access and observe skyrmionic states.
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We report current-induced domain wall motion (CIDWM) in TaCo20Fe60B20MgO nanowires. Domain walls are observed to move against the electron flow when no magnetic field is applied, while a field along the nanowires strongly affects the domain wall motion direction and velocity. A symmetric effect is observed for up-down and down-up domain walls. This indicates the presence of right-handed domain walls, due to a Dzyaloshinskii-Moriya interaction (DMI) with a DMI coefficient D=+0.06 mJ/m2. The positive DMI coefficient is interpreted to be a consequence of boron diffusion into the tantalum buffer layer during annealing. In a PtCo68Fe22B10MgO nanowire CIDWM along the electron flow was observed, corroborating this interpretation. The experimental results are compared to 1D-model simulations including the effects of pinning. This advanced modelling allows us to reproduce the experiment outcomes and reliably extract a spin-Hall angle {theta}SH=-0.11 for Ta in the nanowires, showing the importance of an analysis that goes beyond the currently used model for perfect nanowires.
Antiferromagnetic spintronics is a promising emerging paradigm to develop high-performance computing and communications devices. From a theoretical point of view, it is important to implement simulation tools that can support a data-driven development of materials having specific properties for particular applications. Here, we present a study focusing on antiferromagnetic materials having an easy-plane anisotropy and interfacial Dzyaloshinskii-Moriya interaction (IDMI). An analytical theory is developed and benchmarked against full numerical micromagnetic simulations, describing the main properties of the ground state in antiferromagnets and how it is possible to estimate the IDMI from experimental measurements. The effect of the IDMI on the electrical switching dynamics of the antiferromagnetic element is also analyzed. Our theoretical results can be used for the design of multi-terminal heavy metal/antiferromagnet memory devices.
Chiral magnets are an emerging class of topological matter harbouring localized and topologically protected vortex-like magnetic textures called skyrmions, which are currently under intense scrutiny as a new entity for information storage and processing. Here, on the level of micromagnetics we rigorously show that chiral magnets cannot only host skyrmions but also antiskyrmions as least-energy configurations over all non-trivial homotopy classes. We derive practical criteria for their occurrence and coexistence with skyrmions that can be fulfilled by (110)-oriented interfaces in dependence on the electronic structure. Relating the electronic structure to an atomistic spin-lattice model by means of density-functional calculations and minimizing the energy on a mesoscopic scale applying spin-relaxation methods, we propose a double layer of Fe grown on a W(110) substrate as a practical example. We conjecture that ultrathin magnetic films grown on semiconductor or heavy metal substrates with $C_{2v}$ symmetry are prototype classes of materials hosting magnetic antiskyrmions.
We examine the current-induced dynamics of a skyrmion that is subject to both structural and bulk inversion asymmetry. There arises a hybrid type of Dzyaloshinskii-Moriya interaction (DMI) which is in the form of a mixture of interfacial and bulk DMIs. Examples include crystals with symmetry classes C$_n$ as well as magnetic multilayers composed of a ferromagnet with a noncentrosymmetric crystal and a nonmagnet with strong spin-orbit coupling. As a striking result, we find that, in systems with a hybrid DMI, the spin-orbit-torque-induced skyrmion Hall angle is asymmetric for the two different skyrmion polarities ($pm 1$ given by out-of-plane core magnetization), even allowing one of them to be tuned to zero. We propose several experimental ways to achieve the necessary straight skyrmion motion (with zero Hall angle) for racetrack memories, even without antiferromagnetic interactions or any interaction with another magnet. Our results can be understood within a simple picture by using a global spin rotation which maps the hybrid DMI model to an effective model containing purely interfacial DMI. The formalism directly reveals the effective spin torque and effective current that result in qualitatively different dynamics. Our work provides a way to utilize symmetry breaking to eliminate detrimental phenomena as hybrid DMI eliminates the skyrmion Hall angle.
The Dzyaloshinskii-Moriya interaction (DMI), being one of the origins for chiral magnetism, is currently attracting huge attention in the research community focusing on applied magnetism and spintronics. For future applications an accurate measurement of its strength is indispensable. In this work, we present a review of the state of the art of measuring the coefficient $D$ of the Dzyaloshinskii-Moriya interaction, the DMI constant, focusing on systems where the interaction arises from the interface between two materials. The measurement techniques are divided into three categories: a) domain wall based measurements, b) spin wave based measurements and c) spin orbit torque based measurements. We give an overview of the experimental techniques as well as their theoretical background and models for the quantification of the DMI constant $D$. We analyze the advantages and disadvantages of each method and compare $D$ values in different stacks. The review aims to obtain a better understanding of the applicability of the different techniques to different stacks and of the origin of apparent disagreement of literature values.
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