Naim Ahmad | Searcharxiv

arXiv2024

Stability and Dynamics of Skyrmion and Skyrmion Bags Explored under the Influence of Out-of-Plane Strain and Its Gradient

Skyrmions as well as skyrmion bags in magnetic thin films are promising candidates for future high-density memory devices. The observation of skyrmion bags in liquid crystals and their predicted existence in ferromagnetic films has sparked theoretical studies on current induced dynamics of these topological charges. Here using micromagnetism, we study the impact of out of plane strain on the stability of skyrmion and skyrmion bags in ferromagnetic thin film. We further studied the current induced dynamics in the presence of out of plane strain gradient. We demonstrate that out of plane strain gradient direction with respect to the electron flow can be an efficient way to control the dynamics of topological charges. Specifically, the deflection of skyrmion bags correlates with their topological degree, and an appropriate strain gradient can counteract skyrmion Hall effects, enabling straight-line movement. Our micromagnetic simulations align well with theoretical predictions from the Thiele equation.

cond-mat.mtrl-sci↗

arXiv2024

Tailoring the Growth of $\beta$-Tungsten Using Substrate Bias and Its Effect on FMR-Driven Spin Pumping in $\beta$-W/Py Heterostructures

$\beta$-Tungsten ($\beta$-W), an A15 cubic phase of tungsten, exhibits a giant spin Hall angle compared to its bcc-phase $\alpha$-Tungsten ($\alpha$-W), making high-quality $\beta$-W films desirable for spintronic applications. We report the controlled growth of $\beta$-W films on SiO$_2$/Si substrates via DC sputtering, where substrate bias serves as a critical factor in stabilizing the $\beta$ phase by regulating the energy of deposited atoms. This approach enables the formation of $\beta$-W films over a wide thickness range. Additionally, we studied the spin pumping phenomena in different tungsten phases achieved through substrate bias. Ferromagnetic resonance measurements reveal an enhancement in the magnetic damping ($ \alpha_{\text{eff}} $) for $\beta$-W/Py compared to $\alpha$-W/Py dominated film. The effective spin mixing conductance ($ g_{\text{eff}}^{\uparrow\downarrow} $) is found to be higher in $\beta$-W/Py than in $\alpha$-W/Py, which is attributed to variations in the interface structures between these phases. Importantly, the use of substrate bias does not deteriorate the interface quality, underscoring its effectiveness. These findings highlight the potential of substrate bias in thin-film engineering, paving the way for its advanced utilization in spintronic applications.

cond-mat.mtrl-sci↗