This article reviews static and dynamic interfacial effects in magnetism, focusing on interfacially-driven magnetic effects and phenomena associated with spin-orbit coupling and intrinsic symmetry breaking at interfaces. It provides a historical background and literature survey, but focuses on recent progress, identifying the most exciting new scientific results and pointing to promising future research directions. It starts with an introduction and overview of how basic magnetic properties are affected by interfaces, then turns to a discussion of charge and spin transport through and near interfaces and how these can be used to control the properties of the magnetic layer. Important concepts include spin accumulation, spin currents, spin transfer torque, and spin pumping. An overview is provided to the current state of knowledge and existing review literature on interfacial effects such as exchange bias, exchange spring magnets, spin Hall effect, oxide heterostructures, and topological insulators. The article highlights recent discoveries of interface-induced magnetism and non-collinear spin textures, non-linear dynamics including spin torque transfer and magnetization reversal induced by interfaces, and interfacial effects in ultrafast magnetization processes.

https://link.aps.org/accepted/10.1103/RevModPhys.89.025006

Interface-induced phenomena in magnetism

We present an analytical calculation of the velocity of a single 180° domain wall in a magnetic structure with reduced thickness and/or lateral dimension under the combined action of an external applied magnetic field and an electrical current. As for the case of field-induced domain wall propagation in thick films, two motion regimes with different mobilities are obtained, below and far above the so-called Walker field. Additionally, for the case of current induced motion, a Walker-like current density threshold is defined. The threshold field and current density, stating the wall's internal structure stability, differ from those in thick films; both are reduced by the same geometrical demagnetising factor which accounts for the confinement. This points out the fact that the velocity dependence over an extended field/current range and the knowledge of the Walker breakdown are mandatory to draw conclusions about the phenomenological Gilbert damping parameter tuning the magnetisation dynamics.

https://iopscience.iop.org/article/10.1209/0295-5075/78/57007/pdf

Domain wall mobility, stability and Walker breakdown in magnetic nanowires

Current-induced domain wall motion along high perpendicular magnetocrystalline anisotropy multilayers is studied by means of full micromagnetic simulations and a one-dimensional model in the presence of in-plane fields. We consider domain wall motion driven by the spin Hall effect in the presence of the Dzyaloshinskii-Moriya interaction (DMI). In the case of relatively weak DMI, the wall propagates without significant tilting of the wall plane, and the full micromagnetic results are quantitatively reproduced by a simple rigid one-dimensional model. By contrast, significant wall-plane tilting is observed in the case of strong DMI, and a one-dimensional description including the wall tilting is required to qualitatively describe the micromagnetic results. However, in this strong-DMI case, the one-dimensional model exhibits significant quantitative discrepancies from the full micromagnetic results, in particular, when high longitudinal fields are applied in the direction of the internal domain wall magnetization. It is also shown that, even under thermal fluctuations and edge roughness, the domain wall develops a net tilting angle during its current-induced motion along samples with strong DMI.

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Current-driven dynamics of Dzyaloshinskii domain walls in the presence of in-plane fields: Full micromagnetic and one-dimensional analysis

The microscopic magnetization variation in magnetic domain walls in thin films is a crucial property when considering the torques driving their dynamic behaviour. For films possessing out-of-plane anisotropy normally the presence of Neel walls is not favoured due to magnetostatic considerations. However, they have the right structure to respond to the torques exerted by the spin Hall effect. Their existence is an indicator of the interfacial Dzyaloshinskii-Moriya interaction (DMI). Here we present direct imaging of Neel domain walls with a fixed chirality in device-ready Pt/Co/AlOx films using Lorentz transmission electron and Kerr microscopies. It is shown that any independently nucleated pair of walls in our films form winding pairs when they meet that are difficult to annihilate with field, confirming that they all possess the same topological winding number. The latter is enforced by the DMI. The field required to annihilate these winding wall pairs is used to give a measure of the DMI strength. Such domain walls, which are robust against collisions with each other, are good candidates for dense data storage.

/pdf/magnetic-microscopy-and-topological-stability-of-homochiral-3u5rz34xni.pdf

Magnetic microscopy and topological stability of homochiral Néel domain walls in a Pt/Co/AlOx trilayer.

The magnetic interfacial Dzyaloshinskii–Moriya interaction (DMI) in multilayered thin films can lead to chiral spin states, which are of paramount importance for future spintronic technologies1,2. Interfacial DMI typically manifests as an intralayer interaction, mediated via a paramagnetic heavy metal in systems lacking inversion symmetry3. Here we show that, by designing synthetic antiferromagnets with canted magnetization states4,5, it is also possible to observe direct evidence of the interfacial interlayer DMI at room temperature. The interlayer DMI breaks the symmetry of the magnetic reversal process via the emergence of non-collinear spin states, which results in chiral exchange-biased hysteresis loops. The spin chiral interlayer interactions reported here are expected to manifest in a range of multilayered thin-film systems, opening up as yet unexplored avenues for the development and exploitation of chiral effects in magnetic heterostructures6–8. An interlayer Dzyaloshinskii–Moriya interaction is observed in a synthetic antiferromagnet, with implications for achieving chiral spin textures in multilayered thin films.

/pdf/symmetry-breaking-interlayer-dzyaloshinskii-moriya-2cpymqef0t.pdf

Symmetry-breaking interlayer Dzyaloshinskii–Moriya interactions in synthetic antiferromagnets

Magnetization-reversal processes in a ferromagnetic cobalt film structure (Au/Co/Au), with perpendicular anisotropy, were investigated by magneto-optical magnetometry and microscopy. In the considered ultrathin Co film, the magnetization reversal between the two Ising-spin equilibrium states is dominated by the domain-wall motion mechanism. We focused our studies on processes initiated from a given demagnetized state. Starting from a magnetically saturated state generated under a large field ${\mathrm{H}}_{\mathrm{S}}$, applied perpendicular to the film, this demagnetized state is created through magnetic aftereffects in a field ${\mathrm{H}}_{\mathrm{d}}$ antiparallel but smaller than ${\mathrm{H}}_{\mathrm{S}}$ and applied during a selected time. Direct (${\mathrm{R}}^{\mathrm{D}}$) and indirect (${\mathrm{R}}^{\mathrm{I}}$) magnetization processes are then studied from this state for application of the field parallel and antiparallel to ${\mathrm{H}}_{\mathrm{d}}$, respectively. The dynamics of the magnetization reversal is much faster for the ${\mathrm{R}}^{\mathrm{I}}$ process since it is initiated from a quasihomogeneous 'Swiss cheese' domain state with small nonreversed regions. The magnetic accommodation phenomenon is studied, and a domain-shape memory effect evidenced. A theoretical analysis of the dynamics of magnetization processes is proposed, starting from the model of a patchy inhomogeneous media with a realistic distribution of local coercivities. The pertinent parameters for calculations are deduced from our experimental data using appropriate analytical expressions of the magnetic relaxation time and domain-wall velocity under a field. Computer simulations using these parameters reproduce well the time evolution of the magnetic domain pattern and different magnetization curves both for ${\mathrm{R}}^{\mathrm{D}}$ and ${\mathrm{R}}^{\mathrm{I}}$ magnetization processes.

Magnetization-reversal processes in an ultrathin co/au film

Bloch wall dynamics in ultrathin ferromagnetic films

Magnetization delay recently observed in ultrathin ferromagnetic films has been discussed using the Fatuzzo theory assuming homogeneous magnet. However, the islands structure of ultrathin films is observed for small sample thicknesses. The ‘‘islands’’ model of magnet structure is proposed in the present work for the delay description. It is assumed that the sample is broken at magnetic clusters created by magnetic islands connected by magnetic ‘‘bridges’’ and remagnetization of each cluster undergoes independently. Function describing sample remagnetization is obtained as a sum Ψ(t)=pΨ∞(t)+(1−p)<Ψ(t)≳, where p is the concentration of infinite clusters; Ψ∞(t) is the function from the Fatuzzo theory, and <Ψ(t)≳ is the remagnetization function averaged for a different number of islands in finite clusters. The presented model could be used for analysis of magnetization processes in other magnets consisting of magnetically interacting ‘‘islands.’’

Remagnetization processes of ultrathin magnetic films with islands structure

<h3></h3> В стоматологической практике широко используется свет длиной волны 400—500 nm. Электромагнитные волны данного спектра видимого света имеют оттенки небесных цветов — синего и голубого. Этот свет может быть генерирован лазерной технологией и индуцирован диодными и галогеновыми лампами, а также устройством на основе плазменной дуги. В статье представлены исследования, рассматривающие свойства света длиной волны 400—500 nm и особенности его взаимодействия с живыми клетками и тканями. 

V. V. Tarasenko

Papers

Magnetization-reversal processes in an ultrathin co/au film

Bloch wall dynamics in ultrathin ferromagnetic films

Remagnetization processes of ultrathin magnetic films with islands structure

Properties of light with a wavelength of 400—500 nm

Magnetization reversal processes in ultrathin cobalt films starting from demagnetized states