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To harness the intriguing properties of 2D van der Waals (vdW) ferromagnets (FMs) for versatile applications, the key challenge lies in the reliable material synthesis for scalable device production. Here, the epitaxial growth of single‐crystalline 1T‐CrTe2 thin films on 2‐inch sapphire substrates are demonstrated. Benefiting from the uniform surface energy of the dangling bond‐free Al2O3(0001) surface, the layer‐by‐layer vdW growth mode is observed right from the initial growth stage, which warrants precise control of the sample thickness beyond three monolayer and homogeneous surface morphology across the entire wafer. Moreover, the presence of the Coulomb interaction at the CrTe2/Al2O3 interface plays an important role in tailoring the anomalous Hall response, and the structural optimization of the CrTe2‐based spin‐orbit torque device leads to a substantial switching power reduction by 54%. The results may lay out a general framework for the design of energy‐efficient spintronics based on configurable vdW FMs. [ABSTRACT FROM AUTHOR]

Topological electronic materials hold great promise for revolutionizing spintronics, owing to their topological protected, spin-polarized conduction edge or surface state. One of the key bottlenecks for the practical use of common binary and ternary topological insulator materials is the large defect concentration that leads to a high background carrier concentration. Elemental tin in its α-phase is a room temperature topological semimetal, which is intrinsically less prone to defect-related shortcomings. Recently, the growth of ultrathin α-Sn films on ferromagnetic Co surfaces has been achieved; however, thicker films are needed to reach the 3D topological Dirac semimetallic state. Here, the growth of α-Sn films on Co at cryogenic temperatures was explored. Very low-temperature growth holds the promise of suppressing undesired phases, alloying across the interfaces, as well as the formation of Sn pillars or hillocks. Nevertheless, the critical Sn layer thickness of ≈3 atomic layers, above which the film partially transforms into the undesired b-phase, remains the same as for room-temperature growth. From ferromagnetic resonance studies, and supported by electron microscopy, it can be concluded that for cryogenic Sn layer growth, the interface between Sn and Co remains sharp and the magnetic properties of the Co layer stay intact. [ABSTRACT FROM AUTHOR]

Elemental tin in the α‐phase is an intriguing member of the family of topological quantum materials. In thin films, with decreasing thickness, α‐Sn transforms from a 3D topological Dirac semimetal (TDS) to a 2D topological insulator (TI). Getting access to and making use of its topological surface states is challenging and requires interfacing to a magnetically ordered material. Herein, the successful epitaxial growth of α‐Sn thin films on Co, forming the core of a spin‐valve structure, is reported. Time‐ and element‐selective ferromagnetic resonance experiments are conducted to investigate the presence of spin pumping through the spin‐valve structure. A rigorous statistical analysis of the experimental data using a model based on the Landau–Lifshitz–Gilbert–Slonczewski equation is applied. A strong exchange coupling contribution is found, however no unambiguous proof for spin pumping. Nevertheless, the incorporation of α‐Sn into a spin valve remains a promising approach given its simplicity as an elemental TI and its room‐temperature application potential. [ABSTRACT FROM AUTHOR]

Non-collinear spin structures in materials that combine perpendicular and in-plane magnetic anisotropies are of great technological interest for microwave and spin wave-assisted magnetization switching. [Co/Pt] multilayers are well-known perpendicular anisotropy materials that have the potential to pin the magnetization of a soft magnetic layer, such as permalloy (Py), that has in-plane anisotropy, thereby forming a magnetic exchange spring. Here we report on multilayered [Co/Pt]/Pt/Py films, where an additional ultrathin Pt spacer has been included to control the coupling between the sub-units with in-plane and perpendicular magnetic anisotropy. Vector network analyser (VNA)-ferromagnetic resonance (FMR) measurements were made to obtain a complete picture of the resonant conditions, while the dynamical response of the sub-units was probed by synchrotron-based element- and phase selective x-ray detected FMR (XFMR). For all samples, only slight pinning of the dynamic magnetization of the Py by the [Co/Pt] was noted, and the FMR results were dominated by the 50 nm thick Py layer. Out-of-plane VNA-FMR maps reveal the presence of additional modes, e.g. a perpendicular standing spin-wave (PSSW) state. However, as the magnetic field is reduced below the saturation field, the PSSW state morphs continuously through a series of canted standing spin-wave (CSSW) states into a horizontal standing spin-wave (HSSW) state. The PSSW, CSSW and HSSW states are well described using a multilayer model of the Py film. The observation of CSSW modes is of particular relevance to microwave assisted magnetic recording, where microwave excitation stimulates precession of a soft layer canted out of plane by a pulsed magnetic field. [ABSTRACT FROM AUTHOR]

Few-layer graphene is obtained in atmospheric chemical vapor deposition on polycrystalline copper in a roll-to-roll process. Raman and x-ray photoelectron spectroscopy were employed to confirm the few-layer nature of the graphene film, to map the inhomogeneities, and to study and optimize the growth process. This continuous growth process can be easily scaled up and enables the low-cost fabrication of graphene films for industrial applications. [ABSTRACT FROM AUTHOR]

A three-dimensional singular point that consists of two oppositely aligned emergent monopoles is identified in continuous CoTb thin films, as confirmed by complementary techniques of resonant elastic x-ray scattering, Lorentz transmission electron microscopy, and scanning transmission x-ray microscopy. This new type of topological defect can be regarded as a superposition of an emergent magnetic monopole and an antimonopole, around which the source and drain of the magnetic flux overlap in space. We experimentally prove that the observed spin twist seen in Lorentz transmission electron microscopy reveals the cross section of the superimposed three-dimensional structure, providing a straightforward strategy for the observation of magnetic singularities. Such a quasiparticle provides an excellent platform for studying the rich physics of emergent electromagnetism. [ABSTRACT FROM AUTHOR]