arXiv subjects

Tevfik Onur Menteş

Publications and source records attributed to Tevfik Onur Menteş.

12 recordsLinked to original sources

arXiv2024

Fast current-induced skyrmion motion in synthetic antiferromagnets

Magnetic skyrmions are topological magnetic textures that hold great promise as nanoscale bits of information in memory and logic devices. Although room-temperature ferromagnetic skyrmions and their current-induced manipulation have been demonstrated, their velocity has been limited to about 100 meters per second. In addition, their dynamics are perturbed by the skyrmion Hall effect, a motion transverse to the current direction caused by the skyrmion topological charge. Here, we show that skyrmions in compensated synthetic antiferromagnets can be moved by current along the current direction at velocities of up to 900 meters per second. This can be explained by the cancellation of the net topological charge leading to a vanishing skyrmion Hall effect. Our results open an important path toward the realization of logic and memory devices based on the fast manipulation of skyrmions in tracks.

cond-mat.mes-hall↗

arXiv2023

Unidirectional Nano-Modulated Binding and Electron Scattering in Epitaxial Borophene

A complex interplay between the crystal structure and electron behavior within borophene renders this material an intriguing 2D system with many of its electronic properties still undiscovered. Experimental insight into those properties is additionally hampered by the limited capabilities of the established synthesis methods, which in turn inhibits the realization of potential borophene applications. In this multi-method study, photoemission spectroscopies and scanning probe techniques complemented by theoretical calculations have been used to investigate the electronic characteristics of a high-coverage, single-layer borophene on Ir(111) substrate. Our results show that the binding of borophene to Ir(111) exhibits pronounced one-dimensional modulation and transforms borophene into a nano-grating. The scattering of photoelectrons from this structural grating gives rise to the replication of electronic bands. In addition, the binding modulation is reflected in the chemical reactivity of borophene and gives rise to its inhomogeneous aging effect. Such aging is easily reset by dissolving boron atoms in iridium at high temperature followed by their reassembly into a fresh atomically-thin borophene mesh. Besides proving electron-grating capabilities of the boron monolayer, our data provides a comprehensive insight into the electronic properties of epitaxial borophene which is vital for further examination of other boron systems of reduced dimensionality.

cond-mat.mes-hall↗

arXiv2023

Coexistence of multiple silicene phases in silicon grown on Ag(111)

Silicene, the silicon equivalent of graphene, is attracting increasing scientific and technological attention in view of the exploitation of its exotic electronic properties. This novel material has been theoretically predicted to exist as a free-standing layer in a low-buckled, stable form, and can be synthesized by the deposition of Si on appropriate crystalline substrates. By employing low-energy electron diffraction and microscopy, we have studied the growth of Si on Ag(111) and observed a rich variety of rotationally non-equivalent silicene structures. Our results highlight a very complex formation diagram, reflecting the coexistence of different and nearly degenerate silicene phases, whose relative abundance can be controlled by varying the Si coverage and growth temperature. At variance with other studies, we find that the formation of single-phase silicene monolayers cannot be achieved on Ag(111).

cond-mat.mtrl-sci↗

arXiv2020

Anisotropic skyrmion bubbles in ultra-thin epitaxial Au$_{0.67}$Pt$_{0.33}$/Co/W films

We studied the symmetry of magnetic properties and the resulting magnetic textures in ultra-thin epitaxial Au$_{0.67}$Pt$_{0.33}$/Co/W, a model system exhibiting perpendicular magnetic anisotropy and interface Dzyaloshinskii-Moriya interaction (DMI). As a peculiar feature, the C$_\mathrm{2v}$ crystal symmetry induced by the Co/W interface results in an additional uniaxial in-plane magnetic anisotropy in the cobalt layer. Photoemission electron microscopy with magnetic sensitivity reveals the formation of self-organized magnetic stripe domains oriented parallel to the hard in-plane magnetization axis. We attribute this behavior to the lower domain wall energy when oriented along this axis, where both the DMI and the in-plane magnetic anisotropy favor a Néel domain wall configuration. The anisotropic domain wall energy also leads to the formation of elliptical skyrmion bubbles in a weak out-of-plane magnetic field.

cond-mat.mtrl-sci↗

arXiv2020

In-plane magnetic domains and Néel-like domain walls in thin flakes of the room temperature CrTe$_2$ van der Waals ferromagnet

The recent discovery of magnetic van der Waals materials has triggered a wealth of investigations in materials science, and now offers genuinely new prospects for both fundamental and applied research. Although the catalogue of van der Waals ferromagnets is rapidly expanding, most of them have a Curie temperature below 300 K, a notable disadvantage for potential applications. Combining element-selective x-ray magnetic imaging and magnetic force microscopy, we resolve at room temperature the magnetic domains and domains walls in micron-sized flakes of the CrTe$_2$ van der Waals ferromagnet. Flux-closure magnetic patterns suggesting in-plane six-fold symmetry are observed. Upon annealing the material above its Curie point (315 K), the magnetic domains disappear. By cooling back down the sample, a different magnetic domain distribution is obtained, indicating material stability and lack of magnetic memory upon thermal cycling. The domain walls presumably have Néel texture, are preferentially oriented along directions separated by 120 degrees, and have a width of several tens of nanometers. Besides microscopic mapping of magnetic domains and domain walls, the coercivity of the material is found to be of a few mT only, showing that the CrTe$_2$ compound is magnetically soft. The coercivity is found to increase as the volume of the material decreases.

cond-mat.mtrl-sci↗

arXiv2019

Current-Driven Skyrmion Dynamics and Drive-Dependent Skyrmion Hall Effect in an Ultrathin Film

Magnetic skyrmions are chiral spin textures that hold great promise as nanoscale information carriers. Since their first observation at room temperature, progress has been made in their current-induced manipulation, with fast motion reported in stray-field-coupled multilayers. However, the complex spin textures with hybrid chiralities and large power dissipation in these multilayers limit their practical implementation and the fundamental understanding of their dynamics. Here, we report on the current-driven motion of Néel skyrmions with diameters in the 100-nm range in an ultrathin Pt/Co/MgO trilayer. We find that these skyrmions can be driven at a speed of 100 m/s and exhibit a drive-dependent skyrmion Hall effect, which is accounted for by the effect of pinning. Our experiments are well substantiated by an analytical model of the skyrmion dynamics as well as by micromagnetic simulations including material inhomogeneities. This good agreement is enabled by the simple skyrmion spin structure in our system and a thorough characterization of its static and dynamical properties.

cond-mat.mes-hall↗

arXiv2018

Flux-closure domains in high aspect ratio electroless-deposited CoNiB nanotubes

We report the imaging of magnetic domains in ferromagnetic CoNiB nanotubes with very long aspect ratio, fabricated by electroless plating. While axial magnetization is expected for long tubes made of soft magnetic materials, we evidence series of azimuthal domains. We tentatively explain these by the interplay of anisotropic strain and/or grain size, with magneto-elasticity and/or anisotropic interfacial magnetic anisotropy. This material could be interesting for dense data storage, as well as curvature-induced magnetic phenomena such as the non-reciprocity of spin-wave propagation.

cond-mat.mtrl-sci↗

arXiv2018

Fe intercalation under graphene and hexagonal boron nitride in-plane heterostructure on Pt(111)

Metal nanostructures confined between sp2 hybridized 2D materials and solid supports are attracting attention for their potential application in new nanotechnologies. Model studies under well-defined conditions are valuable for understanding the fundamental aspects of the phenomena under 2D covers. In this work we investigate the intercalation of iron atoms through a single layer of mixed graphene and hexagonal boron nitride on Pt(111) using a combination of spectroscopic and microscopic techniques. Thermally activated diffusion of iron proceeds preferentially under graphene and only partially under hexagonal boron nitride areas. When oxygen is coadsorbed with iron, the intercalation rate is higher, and formation of B2O3 and oxygenated B-C species is observed. Our results suggest the possibility of confining ferromagnetic layers under heterostructures of graphene and hexagonal boron nitride with potential technological implications in the fields of spintronics, magnetic data storage or chemistry under 2D covers.

physics.chem-ph↗

arXiv2017

Electronic properties of WS$_2$ on epitaxial graphene on SiC(0001)

This work reports an electronic and micro-structural study of an appealing system for optoelectronics: tungsten disulphide WS$_2$ on epitaxial graphene (EG) on SiC(0001). The WS$_2$ is grown via chemical vapor deposition (CVD) onto the EG. Low-energy electron diffraction (LEED) measurements assign the zero-degree orientation as the preferential azimuthal alignment for WS$_2$/EG. The valence-band (VB) structure emerging from this alignment is investigated by means of photoelectron spectroscopy measurements, with both high space and energy resolution. We find that the spin-orbit splitting of monolayer WS$_2$ on graphene is of 462 meV, larger than what is reported to date for other substrates. We determine the value of the work function for the WS$_2$/EG to be 4.5$\pm$0.1 eV. A large shift of the WS$_2$ VB maximum is observed as well , due to the lowering of the WS$_2$ work function caused by the donor-like interfacial states of EG. Density functional theory (DFT) calculations carried out on a coincidence supercell confirm the experimental band structure to an excellent degree. X-ray photoemission electron microscopy (XPEEM) measurements performed on single WS$_2$ crystals confirm the van der Waals nature of the interface coupling between the two layers. In virtue of its band alignment and large spin-orbit splitting, this system gains strong appeal for optical spin-injection experiments and opto-spintronic applications in general.

cond-mat.mes-hall↗

arXiv2017

Magnetic skyrmions in confined geometries : effect of the magnetic field and the disorder

We report on the effect of the lateral confinement and a perpendicular magnetic field on isolated room-temperature magnetic skyrmions in sputtered Pt/Co/MgO nanotracks and nanodots. We show that the skyrmions size can be easily tuned by playing on the lateral dimensions of the nanostructures and by using external magnetic field amplitudes of a few mT, which allow to reach sub-100 nm diameters. Our XMCD-PEEM observations also highlight the important role of the pinning on the skyrmions size and stability under an out-of-plane magnetic field. Micromagnetic simulations reveal that the effect of local pinning can be well accounted for by considering the thin film grain structure with local anisotropy variations and reproduce well the dependence of the skyrmion diameter on the magnetic field and the geometry.

cond-mat.mes-hall↗

arXiv2016

Fragmentation of magnetism in artificial kagome dipolar spin ice

Geometrical frustration in magnetic materials often gives rise to exotic, low-temperature states of matter, like the ones observed in spin ices. Here we report the imaging of the magnetic states of a thermally-active artificial magnetic ice that reveal the fingerprints of a spin fragmentation process. This fragmentation corresponds to a splitting of the magnetic degree of freedom into two channels and is evidenced in both real and reciprocal space. Furthermore, the internal organization of both channels is interpreted within the framework of a hybrid spin-charge model that directly emerges from the parent spin model of the kagome dipolar spin ice. Our experimental and theoretical results provide insights into the physics of frustrated magnets and deepen our understanding of emergent fields through the use of tailor-made magnetism.

cond-mat.mes-hall↗

arXiv2012

Angle-resolved X-ray photoemission electron microscopy

Synchrotron based photoemission electron microscopy with energy filter combines real space imaging with microprobe diffraction ($μ$-ARPES), giving access to the local electronic structure of laterally inhomogeneous materials. We present here an overview of the capabilities of this technique, illustrating selected applications of angle resolved photoemission electron microscopy and related microprobe methods. In addition, we report the demonstration of a darkfield XPEEM (df-XPEEM) imaging method for real space mapping of the electronic structure away from $Γ$ at a lateral resolution of few tens of nm. The application of df-XPEEM to the (1$\times$12)-O/W(110) model oxide structure shows the high sensitivity of this technique to the local electronic structure, allowing to image domains with inequivalent adsorption site symmetry. Perspectives of angle resolved PEEM are discussed.

cond-mat.mes-hall↗