Investigating the interactions between a scanning tunneling microscope tip and an Au- coated microcantilever

In this work we investigated the interactions between a tip used for scanning tunnelling microscopy (STM) and a Au-coated cantilever in ambient conditions. A system was constructed to position an STM tip on a Au-coated cantilever. The van der Waals, electrostatic, and capillary forces were used to model the tip-cantilever interactions. As the piezoelectric scanner adjusted the STM tip on the cantilever surface to maintain the tunnelling current set point, the magnitude of the forces changed, causing the deflection of the cantilever to vary. It was noted that the magnitude of the force was affected by the relative humidity and the tip location on the cantilever. Our experimental results showed that the van der Waals, capillary, and repulsive forces dominated the interactions and affected the stability of the cantilever during the interaction with the STM tip. It was found that an attractive force ranging between 2.4 and 27 nN acted on the cantilever when the STM was approaching toward the cantilever. The magnitudes of these forces were varied as the conditions of the experiments changed. In all cases the theoretical estimated values of the force were calculated to be well within the uncertainties. When the separation distance between the STM tip and the cantilever decreased to within a few angstroms, a repulsive force between 80- 86 nN strong was detected

Field-free switching of magnetization in oxide superlattice by engineering the interfacial reconstruction

Spin-orbit torque resulting from non-magnetic materials with strong spin-orbit coupling enables electrically controlled magnetization switching, offering potential applications in ultralow-power memory and logic devices. However, such switching of perpendicular magnetization usually requires an in-plane magnetic field along the applied current direction, which limits its use. To address this challenge, an all-oxide superlattice is designed and fabricated that show both the perpendicular magneto-crystalline anisotropy and in-plane magnetic anisotropies induced by interfacial engineering. The results demonstrate that the coexistence of perpendicular and in plane magnetic anisotropy breaks the symmetry and thus enables the pure electrical switching of perpendicular magnetization.This work was supported by the King Abdullah University of Science and Technology (KAUST), Office of Sponsored Research (OSR), under award Nos. ORA-CRG10-2021-4665 and ORA-CRG11-2022-5031.Peer reviewe

Controllable Skyrmionic Phase Transition between Néel Skyrmions and Bloch Skyrmionic Bubbles in van der Waals Ferromagnet Fe3‐δGeTe2

Abstract The van der Waals (vdW) ferromagnet Fe3‐δGeTe2 has garnered significant research interest as a platform for skyrmionic spin configurations, that is, skyrmions and skyrmionic bubbles. However, despite extensive efforts, the origin of the Dzyaloshinskii–Moriya interaction (DMI) in Fe3‐δGeTe2 remains elusive, making it challenging to acquire these skyrmionic phases in a controlled manner. In this study, it is demonstrated that the Fe content in Fe3‐δGeTe2 has a profound effect on the crystal structure, DMI, and skyrmionic phase. For the first time, a marked increase in Fe atom displacement with decreasing Fe content is observed, transforming the original centrosymmetric crystal structure into a non‐centrosymmetric symmetry, leading to a considerable DMI. Additionally, by varying the Fe content and sample thickness, a controllable transition between Néel‐type skyrmions and Bloch‐type skyrmionic bubbles is achieved, governed by a delicate interplay between dipole–dipole interaction and the DMI. The findings offer novel insights into the variable skyrmionic phases in Fe3‐δGeTe2 and provide the impetus for developing vdW ferromagnet‐based spintronic devices

Controllable Skyrmionic Phase Transition between Néel Skyrmions and Bloch Skyrmionic Bubbles in van der Waals Ferromagnet Fe3‐δGeTe2

The van der Waals (vdW) ferromagnet Fe3-δ GeTe2 has garnered significant research interest as a platform for skyrmionic spin configurations, that is, skyrmions and skyrmionic bubbles. However, despite extensive efforts, the origin of the Dzyaloshinskii-Moriya interaction (DMI) in Fe3-δ GeTe2 remains elusive, making it challenging to acquire these skyrmionic phases in a controlled manner. In this study, it is demonstrated that the Fe content in Fe3-δ GeTe2 has a profound effect on the crystal structure, DMI, and skyrmionic phase. For the first time, a marked increase in Fe atom displacement with decreasing Fe content is observed, transforming the original centrosymmetric crystal structure into a non-centrosymmetric symmetry, leading to a considerable DMI. Additionally, by varying the Fe content and sample thickness, a controllable transition between Néel-type skyrmions and Bloch-type skyrmionic bubbles is achieved, governed by a delicate interplay between dipole-dipole interaction and the DMI. The findings offer novel insights into the variable skyrmionic phases in Fe3-δ GeTe2 and provide the impetus for developing vdW ferromagnet-based spintronic devices

Magnetic Skyrmions with Unconventional Helicity Polarization in a Van Der Waals Ferromagnet.

Skyrmion helicity, which defines the spin swirling direction, is a fundamental parameter that may be utilized to encode data bits in future memory devices. Generally, in centrosymmetric ferromagnets, dipole skyrmions with helicity of -π/2 and π/2 are degenerate in energy, leading to equal populations of both helicities. On the other hand, in chiral materials where the Dzyaloshinskii-Moriya interaction (DMI) prevails and the dipolar interaction is negligible, only a preferred helicity is selected by the type of DMI. However, whether there is a rigid boundary between these two regimes remains an open question. Herein, the observation of dipole skyrmions with unconventional helicity polarization in a van der Waals ferromagnet, Fe5- δ GeTe2 , is reported. Combining magnetometry, Lorentz transmission electron microscopy, electrical transport measurements, and micromagnetic simulations, the short-range superstructures in Fe5- δ GeTe2 resulting in a localized DMI contribution, which breaks the degeneracy of the opposite helicities and leads to the helicity polarization, is demonstrated. Therefore, the helicity feature in Fe5- δ GeTe2 is controlled by both the dipolar interaction and DMI that the former leads to Bloch-type skyrmions with helicity of ±π/2 whereas the latter breaks the helicity degeneracy. This work provides new insights into the skyrmion topology in van der Waals materials