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We have studied the effect of He+ irradiation on the dynamics of chiral domain walls in Pt/Co/AlOx trilayers in the creep regime. Irradiation leads to a strong decrease in the depinning field and a non-monotonous change of the effective pinning barriers. The variations of domain wall dynamics result essentially from the strong decrease in the effective anisotropy constant, which increases the domain wall width. The latter is found to present a perfect scaling with the length-scale of the interaction between domain wall and disorder, ξ. On the other hand, the strength of the domain wall–disorder interaction, fpin, is weakly impacted by the irradiation, suggesting that the length-scales of the disorder fluctuation remain smaller than the domain wall width. [ABSTRACT FROM AUTHOR]

Ferrimagnets are of interest in spintronics owing to the enhancement of spin transfer and spin–orbit torque in the vicinity of the magnetic compensation point. Here, we study the possibility of achieving compensation at room temperature in Mn4−xNixN films grown on SrTiO3(001) substrates by molecular beam epitaxy. The magnetic and magneto-transport properties of 30-nm-thick epitaxial Mn4−xNixN films (x = 0, 0.1, 0.25, and 0.5) were investigated. Ni introduction in Mn4N causes the spontaneous magnetization (MS) to decrease by 45% at x = 0.1 and by 75% at x = 0.25. All samples exhibited the perpendicular magnetic anisotropy required for spintronic applications as well as displaying a sharp magnetization reversal. Remarkably, the sign of the anomalous Hall resistivity changed in the samples between x = 0.1 and 0.25. Further, the magnetization increased for x = 0 and 0.1 and decreased for x = 0.25 when the temperature was decreased. Based on these results, we propose that there is a magnetic compensation composition between x = 0.1 and 0.25, where the magnetization of Mn4−xNixN becomes zero at room temperature. The small MS and perpendicular magnetic anisotropy of the Mn4−xNixN thin films, thus, make them suitable candidates for use in spin transfer torque-based devices. [ABSTRACT FROM AUTHOR]

Focused ion beam irradiation was used to reduce locally the perpendicular anisotropy of magnetic thin films in rectangular lattices of 50 nm sized dots. The effect of the anisotropy patterns, differing in ion fluence and interdot spacing, on the magnetization reversal process was determined in q space with x-ray resonant magnetic scattering and in real space with magnetic force microscopy. At remanence only a slight alignment of the irregularly shaped domains is observed. In perpendicular magnetic fields, however, the high field bubble domains display a pronounced localization on the dots, showing that this form of local anisotropy reduction is a highly efficient way of domain positioning. [ABSTRACT FROM AUTHOR]

Abstract: We review models for the nucleation of magnetisation reversal, i.e. the formation of a region of reversed magnetisation in an initially magnetically saturated system. For small particles, models for collective reversal, either uniform (Stoner–Wohlfarth model) or non-uniform like curling, provide good agreement between theory and experiment. For microscopic objects and thin films, we consider two models, uniform (Stoner–Wohlfarth) reversal inside a nucleation volume and a droplet model, where the free energy of an inverse bubble is calculated, taking into account volume energy (Zeeman energy) and surface tension (domain wall energy). In macroscopic systems, inhomogeneities in magnetic properties cause a distribution of energy barriers for nucleation, which strongly influences effects of temperature and applied field on magnetisation reversal. For these systems, macroscopic material parameters like exchange interaction, spontaneous magnetisation and magnetic anisotropy can give an indication of the magnetic coercivity, but exact values for nucleation fields are, in general, hard to predict. To cite this article: J. Vogel et al., C. R. Physique 7 (2006). [Copyright &y& Elsevier]

Nanoscale magnetic skyrmions are considered as potential information carriers for future spintronics memory and logic devices. Such applications will require the control of their local creation and annihilation, which involves so far solutions that are either energy consuming or difficult to integrate. Here we demonstrate the control of skyrmion bubbles nucleation and annihilation using electric field gating, an easily integrable and potentially energetically efficient solution. We present a detailed stability diagram of the skyrmion bubbles in a Pt/Co/oxide trilayer and show that their stability can be controlled via an applied electric field. An analytical bubble model with the Dzyaloshinskii-Moriya interaction imbedded in the domain wall energy accounts for the observed electrical skyrmion switching effect. This allows us to unveil the origin of the electrical control of skyrmions stability and to show that both magnetic dipolar interaction and the Dzyaloshinskii-Moriya interaction play an important role in the skyrmion bubble stabilization. [ABSTRACT FROM AUTHOR]