Three-dimensional magnetic flux-closure patterns in mesoscopic Fe islands

We have investigated three-dimensional magnetization structures in numerous mesoscopic Fe/Mo(110) islands by means of x-ray magnetic circular dichroism combined with photoemission electron microscopy (XMCD-PEEM). The particles are epitaxial islands with an elongated hexagonal shape with length of up to 2.5 micrometer and thickness of up to 250 nm. The XMCD-PEEM studies reveal asymmetric magnetization distributions at the surface of these particles. Micromagnetic simulations are in excellent agreement with the observed magnetic structures and provide information on the internal structure of the magnetization which is not accessible in the experiment. It is shown that the magnetization is influenced mostly by the particle size and thickness rather than by the details of its shape. Hence, these hexagonal samples can be regarded as model systems for the study of the magnetization in thick, mesoscopic ferromagnets.Comment: 12 pages, 11 figure

Tuning the domain wall orientation in thin magnetic strips by induced anisotropy

We report on a method to tune the orientation of in-plane magnetic domains and domain walls in thin ferromagnetic strips by manipulating the magnetic anisotropy. Uniaxial in-plane anisotropy is induced in a controlled way by oblique evaporation of magnetic thin strips. A direct correlation between the magnetization direction and the domain wall orientation is found experimentally and confirmed by micromagnetic simulations. The domain walls in the strips are always oriented along the oblique evaporation-induced easy axis, in spite of the shape anisotropy. The controlled manipulation of domain wall orientations could open new possibilities for novel devices based on domain-wall propagation

Magnetism in reduced dimensions

We propose a short overview of a few selected issues of magnetism in reduced dimensions, which are the most relevant to set the background for more specialized contributions to the present Special Issue. Magnetic anisotropy in reduced dimensions is discussed, on a theoretical basis, then with experimental reports and views from surface to single-atom anisotropy. Then conventional magnetization states are reviewed, including macrospins, single domains, multidomains, and domain walls in stripes. Dipolar coupling is examined for lateral interactions in arrays, and for interlayer interactions in films and dots. Finally thermally-assisted magnetization reversal and superparamagnetism are presented. For each topic we sought a balance between well established knowledge and recent developments.Comment: 13 pages. Part of a Special Issue of the C. R. Physique devoted to spinelectronics (2005

Interface Magnetoelectric Coupling in Co/Pb(Zr,Ti)O3

Vlašín, Ondřej et al.Magnetoelectric coupling at multiferroic interfaces is a promising route toward the nonvolatile electric-field control of magnetization. Here, we use optical measurements to study the static and dynamic variations of the interface magnetization induced by an electric field in Co/ PbZr0.2Ti0.8O3 (Co/PZT) bilayers at room temperature. The measurements allow us to identify different coupling mechanisms. We further investigate the local electronic and magnetic structure of the interface by means of transmission electron microscopy, soft X-ray magnetic circular dichroism, and density functional theory to corroborate the coupling mechanism. The measurements demonstrate a mixed linear and quadratic optical response to the electric field, which results from a magneto-electto-optical effect. We propose a decomposition method of the optical signal to discriminate between different components involved in the electric field-induced polarization rotation of the reflected light. This allows us to extract a signal that we can ascribe to interface magnetoelectric coupling. The associated surface magnetization exhibits a clear hysteretic variation of odd symmetry with respect to the electric field and nonzero remanence. The interface coupling is remarkably stable over a wide frequency range (1-50 kHz), and the application of a bias magnetic field is not necessary for the coupling to occur. These results show the potential of exploiting interface coupling with the prospect of optimizing the performance of magnetoelectric memory devices in terms of stability, as well as fast and dissipationless operation.This work is supported by the French National Research Agency (ANR) through JCJC program "DYNAMECS” ANR-11-JS10-009-01 and the TEM study was conducted in the framework of project "EMMA” ANR-12-BS10-013. Financial support by the Spanish Government for the CSIC JAE-predoc grant of O.V. is acknowledged. S. C.-H. acknowledges the technical assistance of J.-S. Pelle (IPHC, Strasbourg) and the team of the STnano cleanroom facility in Strasbourg for the optimization of the magnetoelectric micro-devices. R. Cours (CEMES, Toulouse) is acknowledged for his help with the preparation of the sample lamellas for TEM measurements.Peer reviewe

Focusing characteristics of polarized second-harmonic emission at non-Ising polar domain walls

International audienceNon-Ising polar domain walls have recently emerged as individual two-dimensional materials exhibiting localized nonlinear optical emission. The analysis of this emitted light often requires focusing with high apertures. As a result, the vectorial properties of light come into play. This study provides an analytic treatment of the vector light fields' effect on the polarized second-harmonic emission (SHG) arising at polar domain walls. While confined optical fields are expected to alter the SHG polarization response, we identify extrinsic and intrinsic properties capable of canceling focusing effects. We determine a precise combination of the fundamental wave polarization and orientation of the domain walls at which focusing effects are negligible. Furthermore, the perimeter defined by the domain walls intrinsic optical parameters below which focusing effects are negligible is extracted from a systematic focus-dependent analysis. Our study provides the necessary methodology and precautions to probe the internal structure of non-Ising domain walls with confined optical fields, and it can be extended to explore newly discovered ferroelectric topologic nanostructures

Polarization Control of the Interface Ferromagnetic to Antiferromagnetic Phase Transition in Co/Pb(Zr,Ti)O 3

International audienceBased on first-principles calculations, we predict the polarization control of the interfacial magnetic phase and a giant electronically driven magnetoelectric coupling (MEC) in Co/PbZr0.25Ti0.75O3 (PZT)(001). The effect of Co oxidation at the interface shared with (Zr,Ti)O2-terminated PZT is evidenced. The magnetic phase of the oxidized Co interface layer is electrically switched from the ferromagnetic to the antiferromagnetic state by reversing the PZT polarization from upward to downward, respectively. A comparative study between oxidized and unoxidized Co/PZT interfaces shows that in oxidized Co/PZT bilayers, the variation of the interface spin moment upon polarization reversal exceeds that of unoxidized Co/PZT bilayers by about 1 order of magnitude. We define a surface MEC constant αS taking into account the polarization dependence of both the spin and orbital moments. In unoxidized Co/PZT bilayers, we obtain αS ≈ 2 × 10–10 G cm2 V–1, while a giant surface coupling αS ≈ 12 × 10–10 G cm2 V–1 is found in the case of oxidized Co/PZT. We demonstrate that the polarization control of the magnetocrystalline anisotropy via spin–orbit coupling is not only effective at the interface but it extends to the Co film despite the interface origin of the MEC. This study shows that tailoring the nature of atomic bonding and electron occupancies allows for improving the performance of functional interfaces, enabling an efficient electric field control of spin–orbit interactions. Moreover, the nonlocal character of this effect holds promising perspectives for the application of electronically driven interface MEC in spin–orbitronic devices

Three-Dimensional Optical Analysis of Ferroelectric Domain Walls

International audienc

Electric field control of labyrinth domain structures in core-shell ferroelectric nanoparticles

19 pages, 5 figuresIn the framework of the Landau-Ginzburg-Devonshire (LGD) approach, we studied the possibility of controlling the polarity and chirality of equilibrium domain structures by a homogeneous external electric field in a nanosized ferroelectric core covered with an ultra-thin shell of screening charge. Under certain screening lengths and core sizes, the minimum of the LGD energy, which consists of Landau-Devonshire energy, Ginzburg polarization gradient energy, and electrostatic terms, leads to the spontaneous appearance of stable labyrinth domain structures in the core. The labyrinths evolve from an initial polarization distribution consisting of arbitrarily small randomly oriented nanodomains. The equilibrium labyrinth structure is weakly influenced by details of the initial polarization distribution, such that one can obtain a quasi-continuum of nearly degenerate labyrinth structures, whose number is limited only by the mesh discretization density. Applying a homogeneous electric field to a nanoparticle with labyrinth domains, and subsequently removing it, allows inducing changes to the labyrinth structure, as the maze polarity is controlled by a field projection on the particle polar axis