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We report on recent progress in the production and the deposition on surfaces of dielectric materials of self-assembled metallic nanoparticle systems able to organize into branched networks. We emphasize the interest of these new objects for tailoring novel near-field optical properties that could be the basis for optical energy transport in systems of extremely reduced sizes. The experimental optical spectra of such chain networks in solution can be very well reproduced by applying the coupled-dipole approximation scheme. In this paper, we apply this method to investigate the near-field optical properties of self-assembled plasmonic nanoparticle networks deposited on transparent surfaces. [ABSTRACT FROM AUTHOR]

We demonstrate the growth of twin-free Bi2Te3 and Sb2Te3 topological insulators by molecular beam epitaxy and a sizable reduction of the twin density in Bi2Se3 on lattice-matched BaF2(111) substrates. Using X-ray diffraction, electron diffraction and atomic force microscopy, we systematically investigate the parameters influencing the formation of twin domains and the morphology of the films, and show that Se- and Te-based alloys differ by their growth mechanism. Optimum growth parameters are shown to result in intrinsically low-doped films, as probed by angle-resolved photoelectron spectroscopy. In contrast to previous approaches in which twin-free Bi2Se3 films are achieved by increasing the substrate roughness, the quality of our Bi2Te3 is superior on the flattest BaF2 substrates. This finding indicates that, during nucleation, the films not only interact with the topmost atomic substrate layer but also with buried layers that provide the necessary stacking information to promote a single twin, an observation that is supported by ab initio calculations. [ABSTRACT FROM AUTHOR]

The epitaxial growth of MgO on Fe 1 − x V x buffer layers with adjustable lattice parameter is studied by electron diffraction (RHEED) in real time. At the onset of plastic relaxation in the MgO layer, a clear splitting of the diffraction rods is observed in 〈110〉 directions, as well as an increase in their length in the 〈100〉 directions. Splitting along 〈100〉 is also made visible through image background subtraction. These features originate from the surface strain above misfit dislocations, as previously proposed to account for satellite spots in LEED measurements. This explanation is supported by simulations of the diffraction patterns using kinematic diffraction theory. Observation of the diffraction rods splitting is shown to be a powerful way to check the presence of dislocations in MgO tunnel barriers and to accurately determine the critical thickness of plastic relaxation. [ABSTRACT FROM AUTHOR]

Magnetoelectric coupling offers the possibility to change the magnetic state of a material by an applied electric field. Over the last few years, metallic systems have come up as simple prototypes for this interaction. While the previous studies focused on Fe and Co thin films or their alloys, here we demonstrate magnetoelectric coupling in a Ni thin film which is close to a spin-reorientation transition. Our magneto-optic Kerr effect measurements on 10 ML of Ni/Cu(100) show a considerable influence of the applied electric field on the magnetism. This rounds off the range of magnetic metals that exhibit magnetoelectric coupling, and it reveals the possibility of an electric field control of a spin-reorientation transition. [ABSTRACT FROM AUTHOR]

We report a voltage-induced perpendicular magnetic anisotropy (PMA) change in sputter-deposited Ta|CoFeB|MgO and Ru|CoFeB|MgO junctions. The PMA change is quantitatively evaluated by the field dependence of the tunneling magnetoresistance for various bias voltages. We find that both the sign and amplitude of the voltage effect depend on the underlayer, Ta or Ru, below the CoFeB layer. The rf voltage-induced ferromagnetic resonance spectra also support the underlayer-material-dependent direction of the voltage torque. The present study shows that the underlayer is one of the key parameters for controlling the voltage effect. [ABSTRACT FROM AUTHOR]

To examine the influence of the barrier quality in fully epitaxial Fe/MgO/Fe(001) magnetic tunnel junctions (MTJs), we propose to use Fe-V alloys as magnetic electrodes. This leads to a reduced misfit with MgO. We actually observe, by high-resolution electron microscopy (HREM) and local strain measurements, that the misfit dislocations density in the MgO barrier is lower when it is grown on Fe-V(001). This improvement of the crystalline quality of the MgO barrier actually leads to a significant increase of the tunnel magneto-resistance (TMR), despite the loss of spin polarization (SP) in these alloys, which was measured by spin-polarized X-ray photoelectron spectroscopy (SR-XPS). [ABSTRACT FROM AUTHOR]

Two-dimensional and van der Waals ferromagnets are ideal platform to study low-dimensional magnetism and proximity effects in van der Waals heterostructures. Their ultimate two-dimensional character also offers the opportunity to easily adjust their magnetic properties using strain or electric fields. Among 2D ferromagnets, the Cr 1 + x Te2 compounds with x = 0–1 are very promising because their magnetic properties depend on the amount of self-intercalated Cr atoms between pure CrTe2 layers and the Curie temperature ( T C ) can reach room temperature for certain compositions. Here, we investigate the evolution of the composition as well as the structural and magnetic properties of thin Cr1.33Te2 (Cr2Te3) films epitaxially grown on graphene upon annealing. We observe a transition above 450 °C from the Cr1.33Te2 phase with perpendicular magnetic anisotropy and a T C of 180 K to a composition close to Cr 1.39 Te2 with in-plane magnetic anisotropy and a T C of 240–250 K. This phase remains stable up to 650 °C above which a pure Cr film starts to form. This work demonstrates the complex interplay between intercalated Cr, lattice parameters, and magnetic properties in Cr 1 + x Te2 compounds. [ABSTRACT FROM AUTHOR]

The magnetization direction of a metallic magnet has generally been controlled by a magnetic field or by spin-current injection into nanosized magnetic cells. Both these methods use an electric current to control the magnetization direction; therefore, they are energy consuming. Magnetization control using an electric field is considered desirable because of its expected ultra-low power consumption and coherent behaviour. Previous experimental approaches towards achieving voltage control of magnetization switching have used single ferromagnetic layers with and without piezoelectric materials, ferromagnetic semiconductors, multiferroic materials, and their hybrid systems. However, the coherent control of magnetization using voltage signals has not thus far been realized. Also, bistable magnetization switching (which is essential in information storage) possesses intrinsic difficulties because an electric field does not break time-reversal symmetry. Here, we demonstrate a coherent precessional magnetization switching using electric field pulses in nanoscale magnetic cells with a few atomic FeCo (001) epitaxial layers adjacent to a MgO barrier. Furthermore, we demonstrate the realization of bistable toggle switching using the coherent precessions. The estimated power consumption for single switching in the ideal equivalent switching circuit can be of the order of 104kBT, suggesting a reduction factor of 1/500 when compared with that of the spin-current-injection switching process. [ABSTRACT FROM AUTHOR]

The introduction of magnetism in two-dimensional (2D) materials represents an intense field of research nowadays and the quest to reach above-room-temperature ordering temperatures is still underway. Intrinsic ferromagnetismwas discovered in 2017 in CrI3 and Cr2Ge2Te6 in the monolayer formwith low Curie temperatures. An alternative method to introduce magnetism into conventional 2D materials is substitutional doping with magnetic impurities similarly to three-dimensional diluted magnetic semiconductors. The case of Mn-doped transition metal dichalcogenide (MoS2, MoSe2, WS2, WSe2) monolayers is very interesting because combining out-of-plane ferromagnetism and valley contrast leads to ferrovalley materials. In this work, we focus on the incorporation of Mn in MoSe2 by molecular beam epitaxy on graphene which has been rarely addressed up to now. By using a multiscale characterization approach, we demonstrate that Mn atoms are incorporated into the MoSe2 monolayer up to 5 atomic percent. However, when incorporated into the film, Mn atoms tend to diffuse to the grain edges forming undefined MoxMnySez phase at grain boundaries after completion of the MoSe2 monolayer. This segregation leaves the crystalline and electronic structure of MoSe2 unmodified. Above 5%, the saturation of Mn content in MoSe2 leads to the formation of epitaxial MnSe clusters. [ABSTRACT FROM AUTHOR]

Spin-orbit torques, including the Rashba and spin Hall effects, have been widely observed and investigated in various systems. Since interesting spin-orbit torque (SOT) arises at the interface between heavy nonmagnetic metals and ferromagnetic metals, most studies have focused on the ultra-thin ferromagnetic layer with interface perpendicular magnetic anisotropy. Here, we measured the effective longitudinal and transverse fields of bulk perpendicular magnetic anisotropy Pd/FePd (1.54 to 2.43 nm)/MgO systems using harmonic methods with careful correction procedures. We found that in our range of thicknesses, the effective longitudinal and transverse fields are five to ten times larger than those reported in interface perpendicular magnetic anisotropy systems. The observed magnitude and thickness dependence of the effective fields suggest that the SOT do not have a purely interfacial origin in our samples. [ABSTRACT FROM AUTHOR]

Using resonant phenomena to exert coherent control over electron spin dynamics could enable more-energy-efficient spintronic devices and related technologies. Yet, achieving collective spin resonant control by ferromagnetic resonance excitation most often requires radiofrequency magnetic fields or the injection of spin-polarized currents that consume relatively large amounts of power. Inducing ferromagnetic resonances directly with an electric field offers a lower-power alternative to these, but doing so requires strong electric and magnetic coupling that is difficult to realize owing to screening effects, particularly in metallic materials. Here, we demonstrate electric-field-induced ferromagnetic resonance excitation by means of voltage control over the magnetic anisotropy in a few monolayers of FeCo at room temperature. The technique provides a low-power, highly localized and coherent means to manipulate electron spin dynamics. [ABSTRACT FROM AUTHOR]

We investigated pulse voltage-induced dynamic magnetization switchings in magnetic tunneling junctions with a high resistance-area product of 2 kΩ μm2. We found that bistable switching and the oscillatory behavior of switching probability as a function of voltage pulse duration are realized at a lower current density (-1.1 × 105 A/cm2) than in conventional spin-transfer-torque-induced magnetization switching. In addition, the switching probability at different voltage pulse strengths confirmed the existence of a voltage torque induced by a change in perpendicular magnetic anisotropy. This voltage-induced magnetization switching can be a useful technique in future spintronics devices with fast and highly reliable writing processes. [ABSTRACT FROM AUTHOR]