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Register a new userStudy of energetics of 360{deg} domain walls through annihilation
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Added by
Gurucharan V. Karnad
Publication date
2018
fields
Physics
and research's language is
English
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The Dzyaloshinskii-Moriya interaction (DMI) causes domain walls in perpendicular magnetized systems to adopt a homochiral configuration by winding in the same direction for both Up-Down and Down-Up walls. The topology of these domain walls is then distinct from the uniformly magnetized state. When two domain walls approach each other and are in close proximity they form winding pairs, stabilized by a dipolar repulsion. This can result in the formation of 360 {deg} stable domain walls, whose stability is directly related to the magnitude of the additional dipolar interaction resulting from the spin structure governed by the DMI. Application of an external magnetic field can overcome the dipolar repulsion of the winding pairs and result in the annihilation of the domain walls, which is studied here in a combined theoretical and experimental effort. We present an extended analytical model that studies the interaction and modification of the dipolar interaction of the domain wall pairs under the application of in-plane and out-of-plane magnetic fields. We realize the experiment in a system of Ta/Co$_{20}$Fe$_{60}$B$_{20}$/MgO and observe that the results are in agreement with the behavior predicted by the analytical model. To compare and understand these results, we perform micromagnetic calculations to gauge the validity of the analytics and also include the full dipolar interactions which are present due to the device geometry. We find that our numerical and experimental studies are in agreement and that the DMI indeed provides an additional stability mechanism against annihilation of DWs, which is potentially useful in dense memory storage applications. Beyond implications for domain walls, understanding the interaction is an important step to understand and control the interaction of many spin structures that contain domain walls, such as skyrmions.
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The formation of 360{deg} magnetic domain walls (360DWs) in Co and Ni80Fe20 thin film wires was demonstrated experimentally for different wire widths, by successively injecting two 180{deg} domain walls (180DWs) into the wire. For narrow wires (less than 50 nm wide for Co), edge roughness prevented the combination of the 180DWs into a 360DW, and for wide wires (200 nm for Co) the 360DW collapsed, but over an intermediate range of wire widths, reproducible 360DW formation occurred. The annihilation and dissociation of 360DWs was demonstrated by applying a magnetic field parallel to the wire, showing that annihilation fields were several times higher than dissociation fields in agreement with micromagnetic modeling. The annihilation of a 360DW by current pulsing was demonstrated.
The control of domain walls is central to nearly all magnetic technologies, particularly for information storage and spintronics. Creative attempts to increase storage density need to overcome volatility due to thermal fluctuations of nanoscopic domains and heating limitations. Topological defects, such as solitons, skyrmions, and merons, may be much less susceptible to fluctuations, owing to topological constraints, while also being controllable with low current densities. Here, we present the first evidence for soliton/soliton and soliton/antisoliton domain walls in the hexagonal chiral magnet Mn1/3NbS2 that respond asymmetrically to magnetic fields and exhibit pair-annihilation. This is important because it suggests the possibility of controlling the occurrence of soliton pairs and the use of small fields or small currents to control nanoscopic magnetic domains. Specifically, our data suggest that either soliton/soliton or soliton/antisoliton pairs can be stabilized by tuning the balance between intrinsic exchange interactions and long-range magnetostatics in restricted geometries
Recent experimental studies of magnetic domain expansion under easy-axis drive fields in materials with a perpendicular magnetic anisotropy have shown that the domain wall velocity is asymmetric as a function of an external in plane magnetic field. This is understood as a consequence of the inversion asymmetry of the system, yielding a finite chiral Dzyaloshinskii-Moriya interaction. Numerous attempts have been made to explain these observations using creep theory, but, in doing so, these have not included all contributions to the domain wall energy or have introduced additional free parameters. In this article we present a theory for creep motion of chiral domain walls in the creep regime that includes the most important contributions to the domain-wall energy and does not introduce new free parameters beyond the usual parameters that are included in the micromagnetic energy. Furthermore, we present experimental measurements of domain wall velocities as a function of in-plane field that are well decribed by our model, and from which material properties such as the strength of the Dzyaloshinskii-Moriya interaction and the demagnetization field are extracted.
The proliferation of fake news and filter bubbles makes it increasingly difficult to form an unbiased, balanced opinion towards a topic. To ameliorate this, we propose 360{deg} Stance Detection, a tool that aggregates news with multiple perspectives on a topic. It presents them on a spectrum ranging from support to opposition, enabling the user to base their opinion on multiple pieces of diverse evidence.
Antiferromagnets offer remarkable promise for future spintronics devices, where antiferromagnetic order is exploited to encode information. The control and understanding of antiferromagnetic domain walls (DWs) - the interfaces between domains with differing order parameter orientations - is a key ingredient for advancing such antiferromagnetic spintronics technologies. However, studies of the intrinsic mechanics of individual antiferromagnetic DWs remain elusive since they require sufficiently pure materials and suitable experimental approaches to address DWs on the nanoscale. Here we nucleate isolated, 180{deg} DWs in a single-crystal of Cr$_2$O$_3$, a prototypical collinear magnetoelectric antiferromagnet, and study their interaction with topographic features fabricated on the sample. We demonstrate DW manipulation through the resulting, engineered energy landscape and show that the observed interaction is governed by the DWs elastic properties. Our results advance the understanding of DW mechanics in antiferromagnets and suggest a novel, topographically defined memory architecture based on antiferromagnetic DWs.
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