Investigation of Spin-Pumping and -Transport in the Ni80Fe20/Pt/Co Asymmetric Trilayer (original) (raw)
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Journal of Applied Physics, 2019
We present measurements of interfacial Gilbert damping due to the spin pumping effect in Ni 81 Fe 19 /W heterostructures. Measurements were compared for heterostructures in which the crystallographic phase of W, either α(bcc)-W or β(A15)-W, was enriched through deposition conditions and characterized using X-ray diffraction (XRD) and high-resolution cross-sectional transmission electron microscopy (HR-XTEM). Single phase Ni 81 Fe 19 /α-W heterostructures could be realized, but heterostructures with β-W were realized as mixed α-β phase. The spin mixing conductances (SMC) for W at interfaces with Ni 81 Fe 19 were found to be significantly lower than those for similarly heavy metals such as Pd and Pt, but comparable to those for Ta, and independent of enrichment in the β phase.
ACS Applied Materials & Interfaces, 2021
The spin−orbit torque, a torque induced by a charge current flowing through the heavy-metal-conducting layer with strong spin−orbit interactions, provides an efficient way to control the magnetization direction in heavy-metal/ferromagnet nanostructures, required for applications in the emergent magnetic technologies like random access memories, high-frequency nanooscillators, or bioinspired neuromorphic computations. We study the interface properties, magnetization dynamics, magnetostatic features, and spin−orbit interactions within the multilayer system Ti(2)/Co(1)/Pt(0−4)/Co(1)/MgO(2)/Ti(2) (thicknesses in nanometers) patterned by optical lithography on micrometer-sized bars. In the investigated devices, Pt is used as a source of the spin current and as a nonmagnetic spacer with variable thickness, which enables the magnitude of the interlayer ferromagnetic exchange coupling to be effectively tuned. We also find the Pt thickness-dependent changes in magnetic anisotropies, magnetoresistances, effective Hall angles, and, eventually, spin−orbit torque fields at interfaces. The experimental findings are supported by the relevant interface structure-related simulations, micromagnetic, macrospin, as well as the spin drift-diffusion models. Finally, the contribution of the spin−orbital Edelstein−Rashba interfacial fields is also briefly discussed in the analysis.
Physical Review B, 2005
Spin dependent interfacial resistance ͑R I ͒ is crucial for achieving high spin injection efficiency from a ferromagnetic ͑FM͒ metal into a semiconductor ͑SC͒. We present a self-consistent model of spin transport across interfacial resistances at the FM-SC junctions of a FM-SC-FM trilayer structure. The SC layer consists of a highly doped n ++ AlGaAsu GaAs 2DEG while the interfacial resistance at the FM-SC junction is modeled as delta potential ͑␦͒ barriers. The self-consistent scheme consists of a ballistic model of spindependent transmission across the ␦ barriers to evaluate R I , and a drift-diffusion model to obtain the spin-split ⌬ in the electrochemical potentials. The R I values of the two junctions were found to be asymmetric despite the symmetry of the trilayer structure. This asymmetry arises from the finite biasing voltage which causes a difference in electrochemical potentials and spin accumulation at the two interfaces. The effect of R I on the spin-injection efficiency and magnetoresistance is studied over a range of ␦-barrier heights. Significant spininjection efficiency ͑50% ͒ requires high ␦-barrier heights approaching 1 eV. Even higher barrier heights are required to obtain equivalent magnetoresistive effect.
NPG Asia Materials, 2021
Ferromagnetic materials exhibiting low magnetic damping (α) and moderately high-saturation magnetization are required from the viewpoints of generation, transmission, and detection of spin waves. Since spin-to-charge conversion efficiency is another important parameter, high spin mixing conductance ({g_{r}^{\uparrow \downarrow}})(gr↑↓)isthekeyforefficientspin−to−chargeconversion.FullHeusleralloys,e.g.,Co2Fe0.4Mn0.6Si(CFMS),whicharepredictedtobe100( g r ↑ ↓ ) is the key for efficient spin-to-charge conversion. Full Heusler alloys, e.g., Co2Fe0.4Mn0.6Si (CFMS), which are predicted to be 100% spin-polarized, exhibit low α. However,(gr↑↓)isthekeyforefficientspin−to−chargeconversion.FullHeusleralloys,e.g.,Co2Fe0.4Mn0.6Si(CFMS),whicharepredictedtobe100g_r^{ \uparrow \downarrow }gr↑↓attheinterfacebetweenCFMSandaparamagnetisnotfullyunderstood.Here,wereportinvestigationsofspinpumpingandtheinversespinHalleffectinCFMS/Ptbilayers.DampinganalysisindicatesthepresenceofsignificantspinpumpingattheinterfaceofCFMSandPt,whichisalsoconfirmedbythedetectionofaninversespinHallvoltage.WeshowthatinCFMS/Pt,g r ↑ ↓ at the interface between CFMS and a paramagnet is not fully understood. Here, we report investigations of spin pumping and the inverse spin Hall effect in CFMS/Pt bilayers. Damping analysis indicates the presence of significant spin pumping at the interface of CFMS and Pt, which is also confirmed by the detection of an inverse spin Hall voltage. We show that in CFMS/Pt,gr↑↓attheinterfacebetweenCFMSandaparamagnetisnotfullyunderstood.Here,wereportinvestigationsofspinpumpingandtheinversespinHalleffectinCFMS/Ptbilayers.DampinganalysisindicatesthepresenceofsignificantspinpumpingattheinterfaceofCFMSandPt,whichisalsoconfirmedbythedetectionofaninversespinHallvoltage.WeshowthatinCFMS/Pt,g_r^{ \uparrow \downarrow }$$ g r ↑ ↓ (1.70 × 1020 m−2) and ...
High-resolution electron microscopy in spin pumping NiFe/Pt interfaces
Journal of Applied Physics, 2015
In order to understand the effect of the interface on the spin pumping and magnetic proximity effects, high resolution transmission electron microscopy and ferromagnetic resonance (FMR) were used to analyze Py/Pt bilayer and Pt/Py/Pt trilayer systems. The samples were deposited by dc magnetron sputtering at room temperature on Si (001) substrates. The Py layer thickness was fixed at 12 nm in all the samples and the Pt thickness was varied in a range of 0-23 nm. A diffusion zone of approximately 8 nm was found in the Py/Pt interfaces and confirmed by energy dispersive X-ray microanalysis. The FMR measurements show an increase in the linewidth and a shift in the ferromagnetic resonance field, which reach saturation. V C 2015 AIP Publishing LLC.
Spin mediated magneto-electro-thermal transport behavior in Ni80Fe20/MgO/p-Si thin films
Journal of Applied Physics, 2017
In Si, the spin-phonon interaction is the primary spin relaxation mechanism. At low temperatures, the absence of spin-phonon relaxation will lead to enhanced spin accumulation. Spin accumulation may change the electro-thermal transport within the material, and thus may serve as an investigative tool for characterizing spin-mediated behavior. Here, we present the first experimental proof of spin accumulation induced electro-thermal transport behavior in a Pd (1 nm)/Ni80Fe20 (25 nm)/MgO (1 nm)/p-Si (2 μm) specimen. The spin accumulation originates from the spin-Hall effect. The spin accumulation changes the phononic thermal transport in p-Si causing the observed magneto-electro-thermal transport behavior. We also observe the inverted switching behavior in magnetoresistance measurement at low temperatures in contrast to magnetic characterization, which is attributed to the canted spin states in p-Si due to spin accumulation. The spin accumulation is elucidated by current dependent anom...
Tunable spin pumping in exchange coupled magnetic trilayers
Magnetic thin films at ferromagnetic resonance (FMR) leak angular momentum, which may be absorbed by adjacent layers. This phenomenon, known as spin pumping, is manifested by an increase in the resonance linewidth (H), and the closely related Gilbert damping. Another e↵ect of this transfer of spin currents is a dynamical and long-range coupling that drives two magnetic layers into a collective precession when their FMR frequencies coincide. A collective behavior is also found in magnetic trilayers with interlayer exchange coupling (IEC). In this study we investigate the interplay between IEC and spin pumping, using Co/Cu/Py pseudo-spin values. We employ broadband FMR measurements to explore both the frequency and coupling-strength dependence of H. Our observations show that there exists a cut-o↵ frequency, set by the IEC strength, below which the precession is truly collective and the spin pumping is suppressed. These results demonstrate that it is possible to control the spin pumping eciency by varying the frequency or the interlayer exchange coupling. Magnetization dynamics in thin films is the very foundation of emergent technologies within the fields of spin-tronics and magnonics. Two cornerstones for the development of new applications is to tailor the magnetic damping and control the flow of spin currents. The concept of spin pumping describes how the leakage of angular momentum (spin current) from a precessing magnetic film may be absorbed at the interface to another magnetic/non-magnetic layer, which provides an additional damping term [1–3]. The dimensionless damping coecient is then given by ↵ = ↵ (0) + ↵ sp , where ↵ (0) is the intrinsic damping of the precessing layer and ↵ sp is the spin-pumping-induced term. This e↵ect has been extensively studied [4], but the majority of those investigation has focused on the regime where the static coupling between the layers is very weak. The static interlayer exchange coupling (IEC, J 0), is an oscillatory coupling present when two ferromagnetic films (FMs) are separated by a suciently thin nonmag-netic layer (NM) [5, 6]. The coupling will either promote a parallel or antiparallel configuration of the magnetiza-tion in the films, depending on the spacer layer thickness. It can be described within the Ruderman-Kittel-Kasuya-Yosida framework [7] and is therefore often referred to as RKKY-interaction. This theory successfully captures the oscillatory behavior, but quantitative modelling of transition metals needs to account for the itinerant character of the electrons [8]. The ferromagnetic resonance (FMR) of a FM/NM/FM trilayer displays two modes, called the acoustic (in-phase) and optical (out-of-phase) mode, if J 0 is strong enough [9]. While the static IEC is oscillating and short-ranged in nature, there also exists a dynamic and long-ranged coupling between magnetic layers. Two films that precess at the same frequency will synchronize and display a collective behavior in the presence of spin pumping [3, 6]. It is evident that the exploration of the interplay between the static and dynamic interlayer exchange has great prospect of finding new exiting physics. The literature indeed includes a collection of studies on spin pumping in coupled layers [10–14]. However, most of these reports focus on one or a limited number of frequencies. Here we investigate spin pumping in the frequency range of 3-37 GHz using a broadband FMR setup and examine four regimes: strong, intermediate, weak, and zero coupling. The samples are based on Co/Cu/Py trilayers, where the thickness of the Cu spacer sets the strength of the interlayer interaction. The damping is determined by the relation H (f r) = H 0 + 4⇡↵f r / where H is the FWHM of the absorption peak, f r is the resonance frequency, is the gyromagnetic ratio and H 0 is a zero-frequency o↵set [15]. We show that the hybridization between the layers, leading to acoustical and optical modes, is not only dependent on the IEC but also on the field and frequency. The collective nature of the precessions is clear at low fields, as reflected by the relative amplitudes and the field dependence of the resonance frequencies. At higher applied fields the layers behave as single films subjected to an e↵ective field proportional to the interlayer coupling. This transition, from collective to single layer precession, is accompanied by changes in the slope of H vs. f , i.e. the damping, and we attribute those changes to the spin pumping between the layers. The results demonstrate that it is possible to engineer a cut-o↵ frequency, below which the spin pumping is e↵ectively turned o↵. The samples were prepared on oxidized Si-substrates using magnetron sputtering and have the following structure: substrate/seed/Co(80Å)/Cu(d Cu)/Py(45Å)/cap,
Physical review letters, 2017
We identify and investigate thermal spin transport phenomena in sputter-deposited Pt/NiFe_{2}O_{x} (4≥x≥0) bilayers. We separate the voltage generated by the spin Seebeck effect from the anomalous Nernst effect (ANE) contributions and even disentangle the ANE in the ferromagnet (FM) from the ANE produced by the Pt that is spin polarized due to its proximity to the FM. Further, we probe the dependence of these effects on the electrical conductivity and the band gap energy of the FM film varying from nearly insulating NiFe_{2}O_{4} to metallic Ni_{33}Fe_{67}. A proximity-induced ANE could only be identified in the metallic Pt/Ni_{33}Fe_{67} bilayer in contrast to Pt/NiFe_{2}O_{x} (x>0) samples. This is verified by the investigation of static magnetic proximity effects via x-ray resonant magnetic reflectivity.