arXiv subjects

Fehmi Sami Yasin

Publications and source records attributed to Fehmi Sami Yasin.

7 recordsLinked to original sources

arXiv2026

The 2026 Skyrmionics Roadmap

Magnetic skyrmions and related topological spin textures have emerged as a central topic in condensed-matter physics, combining fundamental significance with potential for transformative applications in spintronics, magnonics, and beyond. Over the past decade, advances in material platforms, imaging techniques, theoretical modeling, and device concepts have established skyrmionics as a rapidly expanding field. At the same time, challenges remain in stabilizing, controlling, and integrating such textures into functional architectures, while novel phenomena such as antiskyrmions, higher-order skyrmions, hopfions, and antiferromagnetic textures arise. The 2026 Skyrmionics Roadmap represents a collective effort of many authors, providing a comprehensive perspective on the current state-of-the-art and the outlook for the coming years. In 33 focused sections, each co-authored by two researchers, we chart progress in theory and modeling, material systems, skyrmion dynamics, and skyrmion technologies. By offering a consolidated vision, this Roadmap aims to guide both fundamental research and application-driven efforts, accelerating the transition of skyrmionics from conceptual breakthroughs toward practical technologies.

cond-mat.mes-hall↗

arXiv2025

Domain wall induced topological Hall effect in the chiral-lattice ferromagnet Fe$_x$TaS$_2$

Magnetic topology and its associated emergent phenomena are central to realizing intriguing quantum states and spintronics functionalities. Designing spin textures to achieve strong and distinct electrical responses remains a significant challenge. Layered transition metal dichalcogenides offer a versatile platform for tailoring structural and magnetic properties, enabling access to a wide spectrum of topological magnetic states. Here, we report a domain-wall-driven, large, and tunable topological Hall effect (THE) in a non-centrosymmetric intercalated transition metal dichalcogenides series Fe$_x$TaS$_2$. By systematically varying the Fe intercalation level, we exert precise control over the magnetic ground states, allowing manipulation of the topological Hall effect. Real-space magnetic force microscopy (MFM) provides direct evidence of periodic magnetic stripe domain formation, confirming the microscopic origin of the observed topological transport phenomena. Our findings establish a promising way for tuning the topology of domains to generate substantial electromagnetic responses in layered magnetic materials.

cond-mat.mtrl-sci↗

arXiv2025

Ultralow-Temperature Cryogenic Transmission Electron Microscopy Using a New Helium Flow Cryostat Stage

Advances in cryogenic electron microscopy have opened new avenues for probing quantum phenomena in correlated materials. This study reports the installation and performance of a new side-entry condenZero cryogenic cooling system for JEOL (Scanning) Transmission Electron Microscopes (S/TEM), utilizing compressed liquid helium (LHe) and designed for imaging and spectroscopy at ultra-low temperatures. The system includes an external dewar mounted on a vibration-damping stage and a pressurized, low-noise helium transfer line with a remotely controllable needle valve, ensuring stable and efficient LHe flow with minimal thermal and mechanical noise. Performance evaluation demonstrates a stable base temperature of 6.58 K measured using a Cernox bare chip sensor on the holder with temperature fluctuations within 0.04 K. Complementary in-situ electron energy-loss spectroscopy (EELS) via aluminum bulk plasmon analysis was used to measure the local specimen temperature and validate cryogenic operation during experiments. The integration of cryogenic cooling with other microscopy techniques, including electron diffraction and Lorentz TEM, was demonstrated by resolving charge density wave (CDW) transitions in NbSe2 using electron diffraction, and imaging nanometric magnetic skyrmions in MnSi via Lorentz TEM. This platform provides reliable cryogenic operation below 7 K, establishing a low-drift route for direct visualization of electronic and magnetic phase transformations in quantum materials.

cond-mat.str-el↗

arXiv2025

Skyrmion Bubbles by Design in a Centrosymmetric Kagome Magnet

Topologically protected nanoscale spin textures, such as magnetic skyrmions, have attracted significant interest for spintronics applications. While skyrmions in noncentrosymmetric materials are known to be stabilized by Dzyaloshinskii$-$Moriya interaction (DMI), their deliberate design in centrosymmetric materials remains a challenge. This difficulty largely stems from the complexity of controlling magnetocrystalline anisotropy $-$ a critical factor in the absence of DMI. Here, we demonstrate the chemical tuning of magnetocrystalline anisotropy in the centrosymmetric Kagome magnet TmMn$_6$Sn$_6$. The resulting compound exhibits a spin reorientation transition accompanied by an emergent skyrmion bubble lattice, confirmed by Lorentz transmission electron microscopy. Our findings overcome a key materials design challenge and open possibilities for deliberate design of skyrmionic textures in centrosymmetric systems.

cond-mat.mtrl-sci↗

arXiv2023

Discovery of a Bloch point quadrupole constituting hybrid topological strings

Topological magnetic (anti)skrymions are robust string-like objects heralded as potential components in next-generation topological spintronics devices due to their manipulability via low-energy stimuli such as magnetic fields, heat, and electric/thermal current. While these two-dimensional (2D) topological objects are widely studied, intrinsically three-dimensional (3D) electron-spin real-space topology remains less explored despite its prevalence in bulky magnets. Here, we capture the 3D structure of antiskyrmions in a single-crystal, precision-doped (Fe_{0.63}Ni_{0.3}Pd_{0.07})_{3}P lamellae using holographic vector field electron tomography at room temperature and zero field. Our measurements reveal hybrid string-like solitons composed of skyrmions with topological number W = -1 on the lamellae's surfaces and an antiskyrmion (W = +1) connecting them. High resolution images uncover a Bloch point (BP) quadrupole (four magnetic (anti)monopoles) positioned along the rectangular antiskyrmion's four corners (Bloch lines), which enable the observed lengthwise topological transitions. Furthermore, we calculate and compare the energy densities of hybrid strings with ideal (anti)skyrmion strings using micromagnetic simulations, which suggest that this composite (anti)BP structure stabilizes via the subtle interplay between the magnetostatic interaction and anisotropic Dzyaloshinskii-Moriya interaction. The discovery of these hybrid spin textures enables topological tunabilty, a tunable topological Hall effect, and the suppression of skyrmion Hall motion, disrupting existing paradigms within spintronics.

cond-mat.str-el↗

arXiv2020

Giant anomalous Hall effect from spin-chirality scattering in a chiral magnet

The electrical Hall effect can be significantly enhanced through the interplay of the conduction electrons with magnetism, which is known as the anomalous Hall effect (AHE). Whereas the mechanism related to band topology has been intensively studied towards energy efficient electronics, those related to electron scattering have received limited attention. Here we report the observation of giant AHE of electron-scattering origin in a chiral magnet MnGe thin film. The Hall conductivity and Hall angle respectively reach 40,000 Ω-1cm-1 and 18 % in the ferromagnetic region, exceeding the conventional limits of AHE of intrinsic and extrinsic origins, respectively. A possible origin of the large AHE is attributed to a new type of skew-scattering via thermally-excited spin-clusters with scalar spin chirality, which is corroborated by the temperature-magnetic-field profile of the AHE being sensitive to the film-thickness or magneto-crystalline anisotropy. Our results may open up a new platform to explore giant AHE responses in various systems, including frustrated magnets and thin-film heterostructures.

cond-mat.mtrl-sci↗

arXiv2020

Néel-type skyrmions and their current-induced motion in van der Waals ferromagnet-based heterostructures

Since the discovery of ferromagnetic two-dimensional (2D) van der Waals (vdW) crystals, significant interest on such 2D magnets has emerged, inspired by their appealing properties and integration with other 2D family for unique heterostructures. In known 2D magnets, spin-orbit coupling (SOC) stabilizes perpendicular magnetic anisotropy (PMA). Such a strong SOC could also lift the chiral degeneracy, leading to the formation of topological magnetic textures such as skyrmions through the Dzyaloshinskii-Moriya interaction (DMI). Here, we report the experimental observation of Néel-type chiral magnetic skyrmions and their lattice (SkX) formation in a vdW ferromagnet Fe3GeTe2 (FGT). We demonstrate the ability to drive individual skyrmion by short current pulses along a vdW heterostructure, FGT/h-BN, as highly required for any skyrmion-based spintronic device. Using first principle calculations supported by experiments, we unveil the origin of DMI being the interfaces with oxides, which then allows us to engineer vdW heterostructures for desired chiral states. Our finding opens the door to topological spin textures in the 2D vdW magnet and their potential device application.

cond-mat.mtrl-sci↗