Isotropic spin and inverse spin Hall effect in epitaxial (111)-oriented Pt/Co bilayers

The spin-to-charge current interconversion in bilayers composed of ferromagnetic and nonmagnetic layers with strong spin-orbit coupling has garnered considerable attention due to its exceptional potential in advancing spintronics devices for data storage and logic applications. Platinum (Pt) stands out as one of the most effective materials for generating spin current. While the spin conversion efficiency is isotropic in polycrystalline Pt samples, an ongoing debate persists regarding its dependence on the crystalline direction in single crystalline samples. In this study, we aim to comprehensively evaluate the in-plane anisotropy of spin-charge interconversion using an array of complementary Spin Hall and inverse Spin Hall techniques with both incoherent and coherent excitation. Specifically, we investigate the spin-to-charge interconversion in epitaxial, (111)-oriented, Co/Pt bilayers with low surface roughness, as resulted from x-ray experiments. By varying the thickness of the Pt layer, we gain insights into the spin-charge interconversion in epitaxial Pt and highlight the effects of the interfaces. Our results demonstrate an isotropic behavior within the limits of our detection uncertainty. This finding significantly enhances our understanding of spin conversion in one of the most relevant systems in spintronics and paves the way for future research in this field.Comment: Article accepted for publication in Physical Review Materials, DOI not received ye

Non-equilibrium heating path for the laser-induced nucleation of metastable skyrmion lattices

Understanding formation of metastable phases by rapid energy pumping and quenching has been intriguing scientists for a long time. This issue is crucial for technologically relevant systems such as magnetic skyrmions which are frequently metastable at zero field. Using Atomistic Spin Dynamics simulations, we show the possibility of creating metastable skyrmion lattices in cobalt-based trilayers by femtosecond laser heating. Similar to the formation of supercooled ice droplets in the gas phase, high temperature ultrafast excitation creates magnon drops and their fast relaxation leads to acquisition and quenching of the skyrmion topological protection. The interplay between different processes corresponds to a specific excitation window which can be additionally controlled by external fields. The results are contrasted with longer-scale heating leading to a phase transition to the stable states. Our results provide insight into the dynamics of the highly non-equilibrium pathway for spin excitations and pave additional routes for skyrmion-based information technologies

Non-equilibrium heating path for the laser-induced nucleation of metastable skyrmion lattices

Understanding formation of metastable phases by rapid energy pumping and quenching has been intriguing scientists for a long time. This issue is crucial for technologically relevant systems such as magnetic skyrmions which are frequently metastable at zero field. Using Atomistic Spin Dynamics simulations, we show the possibility of creating metastable skyrmion lattices in cobalt-based trilayers by femtosecond laser heating. Similar to the formation of supercooled ice droplets in the gas phase, high temperature ultrafast excitation creates magnon drops and their fast relaxation leads to acquisition and quenching of the skyrmion topological protection. The interplay between different processes corresponds to a specific excitation window which can be additionally controlled by external fields. The results are contrasted with longer-scale heating leading to a phase transition to the stable states. Our results provide insight into the dynamics of the highly non-equilibrium pathway for spin excitations and pave additional routes for skyrmion-based information technologies

Emergence of the Stoner-Wohlfarth astroid in thin films at dynamic regime

The Stoner-Wohlfarth (SW) model is the simplest model that describes adequately the magnetization reversal of nanoscale systems that are small enough to contain single magnetic domains. However for larger sizes where multi-domain effects are present, e.g., in thin films, this simple macrospin approximation fails and the experimental critical curve, referred as SW astroid, is far from its predictions. Here we show that this discrepancy could vanish also in extended system. We present a detailed angular-dependent study of magnetization reversal dynamics of a thin film with well-defined uniaxial magnetic anisotropy, performed over 9 decades of applied field sweep rate (dH/dt). The angular-dependent properties display a gradual transition from domain wall pinning and motion-like behaviour to a nucleative single-particle one, as dH/dt increases. Remarkably, in the high dynamic regime, where nucleation of reversed domains is the dominant mechanism of the magnetization reversal (nucleative regime), the magnetic properties including the astroid become closer to the ones predicted by SW model. The results also show why the SW model can successfully describe other extended systems that present nucleative regime, even in quasi-static conditionsThis work has been supported by MINECO (Ministerio de Economía y Competitividad) through Projects No. MAT2012-39308, FIS2015-67287-P, and FIS2016-78591-C3-1-R, by the Comunidad de Madrid through Project S2013/MIT-2850 NANOFRONTMAG-CM, and by MINECO through the FLAGERA Programme of Graphene Flagship: SOgraph project (No. PCIN-2015-216); and M-era.Net Programme: NEXMAG project (PCIN- 2015-126). IMDEA-Nanociencia acknowledges support from the ‘Severo Ochoa’ Program for Centres of Excellence in R&D (MINECO, Grant SEV-2016-0686). P.P. acknowledges support through the Marie Curie AMAROUT EU Programme and JCI-2011-09602. A.B. acknowledges MINECO through the ENMA-National project (MAT2014-56955-R)

Engineering the spin conversion in graphene monolayer epitaxial structures

Spin Hall and Rashba-Edelstein effects, which are spin-to-charge conversion phenomena due to spin-orbit coupling (SOC), are attracting increasing interest as pathways to manage rapidly and at low consumption cost the storage and processing of a large amount of data in spintronic devices as well as more efficient energy harvesting by spin-caloritronics devices. Materials with large SOC, such as heavy metals (HMs), are traditionally employed to get large spin-to-charge conversion. More recently, the use of graphene (gr) in proximity with large SOC layers has been proposed as an efficient and tunable spin transport channel. Here, we explore the role of a graphene monolayer between Co and a HM and its interfacial spin transport properties by means of thermo-spin measurements. The gr/HM (Pt and Ta) stacks have been prepared on epitaxial Ir(111)/Co(111) structures grown on sapphire crystals, in which the spin detector (i.e., top HM) and the spin injector (i.e., Co) are all grown in situ under controlled conditions and present clean and sharp interfaces. We find that a gr monolayer retains the spin current injected into the HM from the bottom Co layer. This has been observed by detecting a net reduction in the sum of the spin Seebeck and interfacial contributions due to the presence of gr and independent from the spin Hall angle sign of the HM used

Interfacial spin-orbit driven effects in perpendicular magnetic anisotropy stacks

Tesis doctoral inédita leída en la Universidad Autonoma de Madrid. Fecha de lectura: 24-11-2022