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Register a new userImpact of growth conditions on the domain nucleation and domain wall propagation in Pt/Co/Pt stacks
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Added by
Cynthia P. Quinteros
Publication date
2020
fields
Physics
and research's language is
English
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Understanding the effect of fabrication conditions on domain wall motion in thin films with perpendicular magnetization is a mandatory issue in order to tune their properties aiming to design spintronics devices based on such phenomenon. In this context, the present work intends to show how different growth conditions may affect domain wall motion in the prototypical system Pt/Co/Pt. The trilayers were deposited by dc sputtering, and the parameters varied in this study were the Co thickness, the substrate roughness, and the base pressure in the deposition chamber. Magneto-optical Kerr effect-based magnetometry and microscopy combined with X-ray reflectometry, atomic force microscopy, and transmission electron microscopy were adopted as experimental techniques. This permitted us to elucidate the impact on the hysteresis loops and on the domain wall dynamics, produced by different growth conditions. As other authors, we found that Co thickness is strongly determinant for both the coercive field and the domain wall velocity. On the contrary, the topographic roughness of the substrate and the base pressure of the deposition chamber evidence a selective impact on the nucleation of magnetic domains and on domain wall propagation, respectively, providing a tool to tune these properties.
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We examine the substructures of magnetic domain walls (DWs) in [Pt/(Co/Ni)$_M$/Ir]$_N$ multi-layers using a combination of micromagnetic theory and Lorentz transmission electron microscopy (LTEM). Thermal stability calculations of Q=$pm$1 substructures (2-$pi$ vertical Bloch lines (VBLs) and DW skyrmions) were performed using a geodesic nudged elastic band (GNEB) model, which supports their metastability at room temperature. Experimental variation in strength of the interfacial Dzyaloshinskii-Moriya interaction (DMI) and film thickness reveals conditions under which these substructures are present and enables the formation of a magnetic phase diagram. Reduced thickness is found to favor Q=$pm$1 substructures likely due to the suppression of hybrid DWs. The results from this study provide an important framework for examining 1-D DW substructures in chiral magnetic materials.
We report on magnetic domain wall velocity measurements in ultrathin Pt/Co(0.5-0.8 nm)/Pt films with perpendicular anisotropy over a large range of applied magnetic fields. The complete velocity-field characteristics are obtained, enabling an examination of the transition between thermally activated creep and viscous flow: motion regimes predicted from general theories for driven elastic interfaces in weakly disordered media. The dissipation limited flow regime is found to be consistent with precessional domain wall motion, analysis of which yields values for the damping parameter, $alpha$.
Buckminsterfullerene (C60) can exhibit ferromagnetism at the interface (called as a spinterface) when it is placed next to a ferromagnet (FM). Formation of such spinterface happens due to orbital hybridization and spin polarized charge transfer at the interface. The spinterface can influence the domain size and dynamics of the organic/ferromagnetic heterostructure. Here, we have performed magnetic domain imaging and studied the relaxation dynamics in Pt/Co/C60/Pt system with perpendicular anisotropy. We have compared the results with its parent Pt/Co/Pt system. It is observed that presence of C60 in the Pt/Co/Pt system increases the anisotropy and a decrease in the bubble domain size. Further the switching time of Pt/Co/C60/Pt system is almost two times faster than Pt/Co/Pt system. We have also performed the spin polarized density functional theory (DFT) calculations to understand the underneath mechanism. DFT results show formation of a spin polarized spinterface which leads to an enhancement in anisotropy.
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Chiral domain walls in ultrathin perpendicularly magnetised layers have a N{e}el structure stabilised by a Dzyaloshinskii-Moriya interaction (DMI) that is generated at the interface between the ferromagnet and a heavy metal. Different heavy metals are required above and below a ferromagnetic film in order to generate the structural inversion asymmetry needed to ensure that the DMI arising at the two interfaces does not cancel. Here we report on the magnetic properties of epitaxial Pt/Co/Au$_x$Pt$_{1-x}$ trilayers grown by sputtering onto sapphire substrates with 0.6 nm thick Co. As $x$ rises from 0 to 1 a structural inversion asymmetry is generated. We characterise the epilayer structure with x-ray diffraction and cross-sectional transmission electron microscopy, revealing (111) stacking. The saturation magnetization falls as the proximity magnetisation in Pt is reduced, whilst the perpendicular magnetic anisotropy $K_mathrm{u}$ rises. The micromagnetic DMI strength $D$ was determined using the bubble expansion technique and also rises from a negligible value when $x=0$ to $sim 1$ mJ/m$^2$ for $x = 1$. The depinning field at which field-driven domain wall motion crosses from the creep to the depinning regime rises from $sim 40$ to $sim 70$ mT, attributed to greater spatial fluctuations of the domain wall energy with increasing Au concentration. Meanwhile, the increase in DMI causes the Walker field to rise from $sim 10$ to $sim 280$ mT, meaning that only in the $x = 1$ sample is the steady flow regime accessible. The full dependence of domain wall velocity on driving field bears little resemblance to the prediction of a simple one-dimensional model, but can be described very well using micromagnetic simulations with a realistic model of disorder. These reveal a rise in Gilbert damping as $x$ increases.
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