Effective Spin Mixing Conductance Research Articles

Topological surface state induced spin pumping in sputtered topological insulator (Bi2Te3)–ferromagnet (Co60Fe20B20) heterostructures

Topological insulators with high spin–orbit coupling and helically spin-momentum-locked topological surface states (TSSs) can serve as efficient spin current generators for modern spintronics applications. We used the industrial-friendly DC magnetron sputtering technique to fabricate magnetic heterostructures consisting of Bi2Te3 (BT) as a topological insulator and Co60Fe20B20 (CFB) as a magnetic layer and studied the temperature-dependent spin pumping, utilizing out-of-plane ferromagnetic resonance spectroscopy. These results demonstrate that the effective spin-mixing conductance is significantly affected by the contribution of two-magnon scattering (TMS). It is found that the TMS-free effective spin-mixing conductance increases with decreasing temperature. Additionally, results from magneto-transport measurements indicate that the surface coherence length of BT is in accordance with the temperature-dependent effective spin-mixing conductance. This enhancement of effective mixing conductance correlated with the enhancement in the contribution of the TSSs as evaluated using the weak-anti-localization effect. This study provides a deeper understanding of the temperature-dependent spin dynamics in sputtered BT/CFB heterostructures which can serve as a guide for further exploration of such bilayers for topological-based spintronic applications.

Growth and characterization of the sputtered type-II topological semimetal PdTe2 thin films and PdTe2/Co60Fe20B20 heterostructures

The topological phases such as Dirac/Weyl semimetals are recently observed in Layered transition metal dichalcogenides (TMDs). The family of materials XTe2 (with X = Pd, Pt and Ni) possesses a type-II topological semimetal (TSM) phase. Here, we report the synthesis of the layered XTe2 thin films using the industry-friendly sputtering technique. The structural and morphological qualities of the sputtered-grown XTe2 thin films are analysed using X-ray diffraction and Raman measurements. The crystallites are highly oriented along the c-axis of the sapphire substrate, which suggests that growth is driven by van der Waals epitaxy. The magneto-transport measurements namely temperature-dependent resistivity and magnetoresistance measurement in out-of-plane field configuration are performed on PdTe2 thin films. The semi-metallic trend and superconducting transition are observed in the temperature-dependent resistivity curve. The weak antilocalization behavior observed in the magnetoconductance curves at a low magnetic field signifies the possibility of a non-zero Berry phase, possibly arising from the Dirac fermionic nature of electronic states. The spin dynamics measurements are performed on the PdTe2/Co60Fe20B20 bilayers. The effective spin mixing conductance and spin current density are found to be ∼2×1020m-2and 2.5MAm-2, respectively in PdTe2/Co60Fe20B20 bilayer which are quite larger than those observed in heavy metal-ferromagnets bilayers, and comparable to MBE-grown topological insulator-ferromagnets heterostructures. This work paves the way to synthesize Te-based layered TMDs using the industrially viable sputtering technique, and demonstrates the prospects for exploring the topological superconductive phase in PdTe2 films and large spin-charge conversion efficiency in PdTe2/Co60Fe20B20 heterostructures.

Spin transport characteristics modulated by the GeBi interlayer in Y3Fe5O12/GeBi/Pt heterostructures

For the past few years, germanium-based semiconductor spintronics has attracted considerable interest due to its potential for integration into mainstream semiconductor technology. The main challenges in the development of modern semiconductor spintronics are the generation, detection, and manipulation of spin currents. Here, the transport characteristics of a spin current generated by spin pumping through a GeBi semiconductor barrier in Y3Fe5O12/GeBi/Pt heterostructures were investigated systematically. The effective spin-mixing conductance and inverse spin Hall voltage to quantitatively describe the spin transport characteristics were extracted. The spin-injection efficiency in the Y3Fe5O12/GeBi/Pt heterostructures is comparable to that of the Y3Fe5O12/Pt bilayer, and the inverse spin Hall voltage exponential decays with the increase in the barrier thickness. Furthermore, the band gap of the GeBi layer was tuned by changing the Bi content. The spin-injection efficiency at the YIG/semiconductor interface and the spin transportation within the semiconductor barrier are related to the band gap of the GeBi layer. Our results may be used as guidelines for the fabrication of efficient spin transmission structures and may lead to further studies on the impacts of different kinds of barrier materials.

Comparative Study of Spin Pumping in Epitaxial- and Polycrystalline-NiO/Ni80Fe20

We perform a comparative study of spin pumping in NiO/Ni[Formula: see text]Fe[Formula: see text] (Py) by altering the crystallinity of NiO. We simultaneously grow high-quality NiO/Py heterostructures on Si/SiO2 and Al2O3(0001) substrates. Although the growth on Si/SiO2 substrate produced polycrystalline NiO (Poly-NiO), the growth on Al2O3(0001) substrate produced epitaxial NiO (Epi-NiO). Our ferromagnetic resonance measurements reveal the presence of two-magnon scattering (TMS) in the measured linewidth for the Epi-NiO/Py system. By carefully considering the contribution of TMS, we found the effective spin mixing conductance, g[Formula: see text] to be comparable in both Poly-NiO/Py and Epi-NiO/Py, despite the different crystallinity of NiO. Our findings show that g[Formula: see text] of an optimized polycrystalline-NiO/Py system can reach the value for an epitaxial-NiO/Py system.

Optimizing spin pumping and spin mixing conductance via Cu spacer layer in Mn2Au/Py system

Switching magnetization with spin current via spin orbital torque is a novel approach towards energy-efficient spintronics. In this regard, high spin–orbit coupling materials such as heavy metals are required to create the spin current via spin Hall effect. In recent times, a lot of attention has been paid to replace heavy metals by antiferromagnets to be considered as a spin sink. The bimetallic antiferromagnet, Mn2Au has attracted interest due to its high Néel temperature (T N > 1000 K) and high spin Hall angle. Here, we present results from experiments on spin pumping and the inverse spin Hall effect (ISHE) employing ferromagnetic resonance in Mn2Au/Py and Mn2Au/Cu/Py systems. The values of Gilbert damping constant decrease while inverse spin Hall voltage increases with the insertion of Cu spacer layer. This unusual behaviour indicates that the interface plays an important role for tuning the spintronic parameters. The maximum effective spin mixing conductance () has been evaluated to be 36.20 × 1018 m−2.

Magnetization dynamics in layered systems with coexisting bilinear and biquadratic interlayer exchange coupling

Important aspects of exchange-coupled magnetic layered structures are related to the noncollinear arrangement of sublayer magnetizations which can arise from competition between bilinear (BL) and biquadratic (BQ) interlayer exchange coupling (IEC). In this work, the influence of coexisting BL and BQ IEC of different strengths on magnetization precession in layered systems is investigated both experimentally and theoretically. Laser-induced magnetization precession has been studied in the $\text{Fe/Si}({d}_{\text{Si}}$) multilayers (MLS) as a function of the amplitude ($H$) and orientation angle (${\ensuremath{\theta}}_{H}$) of external magnetic field using time-resolved magneto-optical Kerr (TRMOKE) effect. Strongly changing characters of precession frequency dependencies $\ensuremath{\omega}(H,{\ensuremath{\theta}}_{H})$ for Fe sublayer thickness ${d}_{\text{Fe}}=3$ nm and Si spacer-layer thicknesses (${d}_{\text{Si}}$) varying in the range of 0.9--2.4 nm have been observed. Analytical formulas for acoustic and optic mode dispersion relations with coexisting BL and BQ IEC, scaled by ${J}_{1}$ and ${J}_{2}$ parameters, respectively, for the in-plane effective magnetic anisotropy and arbitrary magnetic field direction were derived, and very good agreement with the experimentally observed frequency dependencies has been obtained. It is shown that BQ coexisting with BL IEC significantly influences on the magnitude and form of dispersion relations. From analytical formula derived, it follows that zero-field optical mode frequency tends to zero as $|{J}_{1}|$ approaches $2{J}_{2}$. The acoustic and optic mode-crossing effect has been observed and it is found that values of crossing fields and frequency gaps strongly increase as ${\ensuremath{\theta}}_{H}$ angles decrease and depend on relative BL and BQ IEC strengths. The BL IEC is of ferromagnetic type with ${J}_{1}\ensuremath{\approx}1.6$ mJ/${\mathrm{m}}^{2}$ for the MLS with ${d}_{\text{Si}}=0.9$ nm, and changes to antiferromagnetic one with ${J}_{1}\ensuremath{\approx}\ensuremath{-}0.9$ mJ/${\mathrm{m}}^{2}$ for the MLS with ${d}_{\text{Si}}=1.4$ nm, while the ${J}_{2}$ parameter of BQ IEC decreases from 1.8 to 1.0 mJ/${\mathrm{m}}^{2}$. The coupling strengths decrease by one to two orders of magnitude for the sample with ${d}_{\text{Si}}=2.4$ nm, but both mode frequencies are still observed and well reproduced by the theory. It is shown that ${J}_{1}$ and ${J}_{2}$ parameters obtained in the TRMOKE experiment coincide within the estimated error bars with the determined from independent measurements of magnetization processes in the static magneto-optical Kerr effect and interpreted with the use of analytical formulas derived. Numerical solutions of coupled Landau-Lifshitz-Gilbert (LLG) equations for acoustic and optic modes, with inclusion of BL IEC, intrinsic Gilbert damping, and spin-pumping damping terms, and extended to include BQ IEC, were performed and fitted to experimental data. It is shown that determined effective damping coefficients on $H$ and ${\ensuremath{\theta}}_{H}$ dependencies for acoustic and optic modes are very well simulated with the use of LLG equation solutions with Gilbert damping, spin-pumping-damping--related effective spin-mixing conductance, and spin-diffusion length parameters included. The dependencies of the parameters on ${d}_{\text{Si}}$ spacer-layer thickness are discussed and compared with available data for other systems.

Interfacial Tuning of Anisotropic Gilbert Damping

Tuning of the anisotropic Gilbert damping Δα has been realized in ultrathin single-crystalline Fe films grown on GaAs (001). A nonmonotonic dependence of Δα on film thickness t is observed upon varying t about 10ML (∼1.4 nm). Δα increases for 16 ML>t>8.5 ML, and then decreases for 8.5 ML>t>6.5 ML accompanied by a sign reversal of Δα for t=6.5 ML. The sign reversal of Δα is captured by first-principle calculations, which show that the anisotropic density of states changes sign upon decreasing t. Moreover, t^{-1} dependence of the anisotropic damping indicates the emergence of an anisotropic effective spin mixing conductance according to the theory of spin pumping. The results establish new opportunities for controlling the Gilbert damping and for fundamental studies of magnetization dynamics in reduced dimension.

Automated mechanical exfoliation technique: a spin pumping study in YIG/TMD heterostructures.

Spintronics devices rely on the generation and manipulation of spin currents. Two-dimensional transition-metal dichalcogenides (TMDs) are among the most promising materials for a spin current generation due to a lack of inversion symmetry at the interface with the magnetic material. Here, we report on the fabrication of Yttrium Iron Garnet(YIG)/TMD heterostructures by means of a crude and fast method. While the magnetic insulator single-crystalline YIG thin films were grown by magnetron sputtering, the TMDs, namely MoS2 and MoSe2, were directly deposited onto YIG films using an automated mechanical abrasion method. Despite the brute force aspect of the method, it produces high-quality interfaces, which are suitable for spintronic device applications. The spin current density and the effective spin mixing conductance were measured by ferromagnetic resonance, whose values found are among the highest reported in the literature. Our method can be scaled to produce ferromagnetic materials/TMD heterostructures on a large scale, further advancing their potential for practical applications.

High temperature stability in few atomic layer MoS2 based thin film heterostructures: structural, static and dynamic magnetization properties.

Layered transition metal dichalcogenides (TMDs) have shown commendable properties for spintronic applications. From the device perspective, the structural quality of the TMD as well as its interface with the adjacent ferromagnetic (FM) layer is of paramount importance. Here, we present the spin-dynamic behaviour in the widely studied TMDs, i.e., MoS2 using Co60Fe20B20 (CoFeB), i.e., in MoS2(1-4 layers)/CoFeB(4-15 nm) heterostructures, both in the as-grown state and in the in situ annealed state (400 °C in a vacuum). Raman spectroscopy revealed systematic variation in the separation (δ) between the characteristic Raman shifts corresponding to the E2g and A1gvis-à-vis the number of layers (nL) of MoS2. The analysis of the ferromagnetic resonance (FMR) spectroscopy measurements performed on these heterostructures revealed the spin pumping from CoFeB to the MoS2 layer as evidenced by the ∼49% (∼51%) enhancement in the effective damping parameter with respect to the damping parameter of bare as-deposited (annealed) CoFeB films. This enhancement is attributed to the spin-pumping owing to the high spin-orbit coupling of monolayer MoS2. The latter is also confirmed by density functional theory calculations. By finding the effective spin mixing conductance of the MoS2/CoFeB interface, the effective spin current density in the MoS2 layer is estimated to increase from ∼0.3 to 0.7 MA m-2 with CoFeB thickness for both the as-deposited and annealed heterostructures. Furthermore, the δ vs. nL curve of the as-deposited heterostructure did not show any significant change upon annealing, which demonstrated that the spin transport and magnetic properties of these heterostructures remained unaffected even after annealing at a high temperature of 400 °C. Hence, this establishes the high thermal stability of the sputter grown MoS2/CoFeB heterostructures. Thus, this study highlights the important role of MoS2 as an efficient spin current-generating source for spin-orbit torque based magnetic memory applications, given the high-temperature stability and high-quality monolayers of MoS2 and its excellent performance with CoFeB thin films.

Large enhancement of magnetic damping in half-metallic Co2MnSi Heusler alloy thin films with heavy metal Pt layer observed by the all-optical method

Manipulation of magnetic moments through spin transport is determined by the effective spin mixing conductance g eff ↑↓ in the ferromagnetic metal/heavy metal heterostructure. Magnetization dynamics detection and evaluation of the Gilbert damping constant α is usually employed to estimate g eff ↑↓. An all-optical pump-probe method is a powerful method for investigating α with high accuracy because an extrinsic contribution on α can be suppressed at a high precession frequency with an increasing external magnetic field. A large voltage signal was recently observed in half-metallic Heusler alloy Co2MnSi thin film due to spin current injection; however, that voltage signal may also include contributions from thermal effect and spin Hall angle in the heavy metal layer. In this study, a large enhancement of α was observed in Co2MnSi/Pt heterostructure by using the all-optical method. g eff ↑↓ for Co2MnSi/Pt was 2 times larger than that for Fe/Pt. This large g eff ↑↓ is promising for spintronic device applications.

Effect of Cu Intercalation Layer on the Enhancement of Spin-to-Charge Conversion in Py/Cu/Bi2Se3.

The spin-to-charge conversion in Permalloy (Py)/Cu/Bi2Se3 is tunable by changing the Cu layer thickness. The conversion rate was studied using the spin pumping technique. The inverse Edelstein effect (IEE) length λIEE is found to increase up to ~2.7 nm when a 7 nm Cu layer is introduced. Interestingly, the maximized λIEE is obtained when the effective spin-mixing conductance (and thus Js) is decreased due to Cu insertion. The monotonic increase in λIEE with decreasing Js suggests that the IEE relaxation time (τ) is enhanced due to the additional tunnelling barrier (Cu layer) that limits the interfacial transmission rate. The results demonstrate the importance of interface engineering in the magnetic heterostructure of Py/topological insulators (TIs), the key factor in optimizing spin-to-charge conversion efficiency.

Spin pumping in nanolayers of WS2/Co2FeAl heterostructures: Large spin mixing conductance and spin transparency

Materials with high spin–orbit coupling (SOC) are a prerequisite for the realization of spin–orbit torque-based magnetic memories. Transition metal dichalcogenides (TMDs) are an apt choice for such applications due to their high SOC strength. In this work, we have investigated the spin pumping phenomenon at the interface between thin tungsten disulphide (WS2) films and Co2FeAl (CFA) Heusler alloy films by performing ferromagnetic resonance (FMR) measurements on WS2/CFA heterostructures capped with the 4 nm thin Al film. While Raman spectroscopy conclusively proves the number of monolayers in the WS2 films, atomic force microscopy and x-ray reflectivity measurements were used to quantify the smoothness of the grown interfaces (<0.4 nm) as well as the individual layer thicknesses in the heterostructure stacks. Here, we vary the WS2 layer numbers and CFA thicknesses to quantify the spin pumping parameters such as spin mixing conductance, and spin transparency. FMR measurements revealed that damping enhancement reached ∼41% with a monolayer of WS2. Interfacial effective spin mixing conductance and spin transparency of the WS2/CFA interface are found to be 7.47 ± 0.97 nm−2 and 73.35 ± 9.52%, respectively. Thus, high-quality TMDs can be used as efficient materials for magnetic memory device applications.

High spin mixing conductance and spin transparency in ion-beam sputtered Ta/Co60Fe20B20 bilayers on Si (100)

Ta/CoFeB heterostructure has been considered as a promising structure for spin torque-based memory applications. Here, a systematic investigation of the magnetic (static and dynamic) properties of ion-beam sputtered Ta/Co60Fe20B20(CFB) bilayer thin films has been done. In the series, the thickness of CFB (tCFB) layer is varied from 2 to 24 nm, keeping the buffer Ta layer thickness fixed at 5 nm as a spin sink reservoir. The structural studies reveal a mixed phase (α+β) growth of Ta layer, while CFB is amorphous, and the interface between them is quite smooth with extremely low interface roughness (<3Å). The saturation magnetization is found to be increased from 957(±30) kA/m to 1097(±19) kA/m with tCFB while the coercivity lies in the range of 0.18-0.75 mT, suggesting the highly soft magnetic nature of the CFB films. Ferromagnetic resonance spectroscopy was performed to study the spin pumping response of the Ta/CFB bilayer thin films. From the variation of effective magnetization with tCFB, surface anisotropy energy of the CFB film is calculated to be 0.24±0.07 erg/cm2. From the effective damping change with tCFB, the effective spin mixing conductance (geff↑↓) and transparency (T) of the Ta/CFB interface are extracted and found to be 11.74±1.14 nm−2 and 60.61±5.88 %, respectively. The origin of large geff↑↓ and T lies at the smooth interface between Ta and CFB. Such a large values of these parameters in Ta/CFB heterostructures are essential requirements for spin device applications.

Enhancement of spin-orbit torque efficiency by tailoring interfacial spin-orbit coupling in Pt-based magnetic multilayers

We study inserting Co layer thickness-dependent spin transport and spin–orbit torques (SOTs) in the Pt/Co/Py trilayers by spin-torque ferromagnetic resonance. The interfacial perpendicular magnetic anisotropy (IPMA) energy density (K s = 2.7 erg/cm2, 1 erg = 10−7 J), which is dominated by interfacial spin–orbit coupling (ISOC) in the Pt/Co interface, total effective spin-mixing conductance ) and two-magnon scattering (β TMS = 0.46 nm2) are first characterized, and the damping-like torque (ξ DL = 0.103) and field-like torque (ξ FL = –0.017) efficiencies are also calculated quantitatively by varying the thickness of the inserting Co layer. The significant enhancement of ξ DL and ξ FL in Pt/Co/Py than Pt/Py bilayer system originates from the interfacial Rashba–Edelstein effect due to the strong ISOC between Co-3d and Pt-5d orbitals at the Pt/Co interface. Additionally, we find a considerable out-of-plane spin polarization SOT, which is ascribed to the spin anomalous Hall effect and possible spin precession effect due to IPMA-induced perpendicular magnetization at the Pt/Co interface. Our results demonstrate that the ISOC of the Pt/Co interface plays a vital role in spin transport and SOTs-generation. Our finds offer an alternative approach to improve the conventional SOTs efficiencies and generate unconventional SOTs with out-of-plane spin polarization to develop low power Pt-based spintronic via tailoring the Pt/FM interface.

Generation of terahertz transients from Co2Fe0.4Mn0.6Si Heusler alloy/heavy-metal bilayers

We generated pulses of electromagnetic radiation with a frequency content up to three terahertz (THz) by optical excitation of Co2Fe0.4Mn0.6Si Heusler alloy/heavy metal bilayers (CFMS/HM) using fs-laser pulses. We attribute the generation process to the conversion of a spin current, generated by the illumination with a fs-laser pulse, to a charge current via the inverse spin Hall effect. We compared the THz emission efficiency in CFMS/Pt and CFMS/Ta bilayers due to their high spin–orbit coupling of Pt and Ta. Surprisingly, our data reveal that CFMS/Pt shows substantially larger THz amplitudes compared to CFMS/Ta. Both bilayers exhibit a tunability of the THz amplitude by external magnetic field both at 300 K and 100 K. Ferromagnetic resonance measurements demonstrate that CFMS/Ta has a high effective spin mixing conductance, describing the efficiency of interfacial spin transport. We observe that the efficiency of the THz radiation cannot be solely described by the spin–orbit coupling strength and the spin diffusion length in the HM material plays an important role.

High spin pumping efficiency in Fe80Co20/Ta bilayers

We have investigated the spin pumping phenomenon in Fe80Co20/Ta bilayers of different thicknesses in which the ferromagnet grows epitaxially on MgO substrates. We have obtained a Gilbert damping constant for Fe80Co20 as low as α = 1.3(1) × 10−3, which is smaller than values generally reported in metallic ferromagnets. From the dependence of α with the Fe80Co20 thickness, we extracted the value of the effective spin mixing conductance = 5.7(3) × 1014 cm−2. Analyzing the Ta and Fe80Co20 thickness dependence of the inverse spin Hall effect voltage, we obtained the transport parameters = 1.1(3) nm and = –0.024(3). We have developed an expression to quantify the efficiency of the spin pumping phenomenon in ferromagnetic/nonmagnetic metal bilayers. The calculated efficiency shows that the Fe80Co20/Ta system is up to an order of magnitude more efficient than other metallic ferromagnetic bilayers reported in the literature.

Structural Phase-Dependent Giant Interfacial Spin Transparency in W/CoFeB Thin-Film Heterostructures.

Pure spin current has transformed the research field of conventional spintronics due to its various advantages, including energy efficiency. An efficient mechanism for generation of pure spin current is spin pumping, and high effective spin-mixing conductance (Geff) and interfacial spin transparency (T) are essential for its higher efficiency. By employing the time-resolved magneto-optical Kerr effect technique, we report here a giant value of T in substrate/W (t)/Co20Fe60B20 (d)/SiO2 (2 nm) thin-film heterostructures in the beta-tungsten (β-W) phase. We extract the spin diffusion length of W and spin-mixing conductance of the W/CoFeB interface from the variation of damping as a function of W and CoFeB thickness. This leads to a value of T = 0.81 ± 0.03 for the β-W/CoFeB interface. A stark variation of Geff and T with the thickness of the W layer is obtained in accordance with the structural phase transition and resistivity variation of W with its thickness. Effects such as spin memory loss and two-magnon scattering are found to have minor contributions to damping modulation in comparison to the spin pumping effect which is reconfirmed from the unchanged damping constant with the variation of Cu spacer layer thickness inserted between W and CoFeB. The giant interfacial spin transparency and its strong dependence on crystal structures of W will be important for future spin-orbitronic devices based on pure spin current.

Fully Spin-Transparent Magnetic Interfaces Enabled by the Insertion of a Thin Paramagnetic NiO Layer

Spin backflow and spin-memory loss have been well established to considerably lower the interfacial spin transmissivity of metallic magnetic interfaces and thus the energy efficiency of spin-orbit torque technologies. Here, we report that spin backflow and spin-memory loss at Pt-based heavy metal-ferromagnet interfaces can be effectively eliminated by inserting an insulating paramagnetic NiO layer of optimum thickness. The latter enables the thermal magnon-mediated essentially unity spin-current transmission at room temperature due to considerably enhanced effective spin-mixing conductance of the interface. As a result, we obtain dampinglike spin-orbit torque efficiency per unit current density of up to 0.8 as detected by the standard technology ferromagnet FeCoB and others, which reaches the expected upper-limit spin Hall ratio of Pt. We establish that Pt/NiO and Pt-Hf/NiO are two energy-efficient, integration-friendly, and high-endurance spin-current generators that provide >100 times greater energy efficiency than sputter-deposited topological insulators BiSb and BiSe. Our finding will benefit spin-orbitronic research and advance spin-torque technologies.

Highly efficient charge-to-spin conversion from in situ Bi2Se3/Fe heterostructures

Topological insulators (TIs) show bright prospects in exerting spin–orbit torques (SOTs) and inducing magnetization switching in the adjacent ferromagnetic (FM) layer. However, a variation of the SOT efficiency values may be attributed to the ex situ deposition of the FM layer or the complex capping/decapping processes of the protection layer. We have employed an in situ fabrication of Bi2Se3/Fe heterostructures and investigated the SOT efficiency by spin torque ferromagnetic resonance. An enhanced SOT efficiency and large effective spin mixing conductance have been obtained especially below 100 K as compared with ex situ methods. The enhancement of the SOT efficiency is attributed to a much thinner interfacial layer (0.96 nm) in the in situ case and thus the enhanced interface spin transparency. Our results reveal the crucial role of interface engineering in exploring highly efficient TI-based spintronic devices.

Enhanced spin-orbit torque efficiency in Pt100–x Ni x alloy based magnetic bilayer* *Project supported by the National Natural Science Foundation of China (Grant Nos. 51901025 and 51625101), the Fundamental Research Funds for the Central Universities, China (Grant No. 310421101), and the Beijing Natural Science Foundation, China (Grant No. Z190007).

The binary alloy/ferromagnetic metal heterostructure has drawn extensive attention in the research field of spin–orbit torque (SOT) due to the potential enhancement of SOT efficiency via composition engineering. In this work, the magnetic properties and SOT efficiency in the Pt100 – x Ni x /Ni78Fe22 bilayers were investigated via the spin-torque ferromagnetic resonance (ST-FMR) technique. The effective magnetic anisotropy field and effective damping constant extracted by analyzing the ST-FMR spectra show a weak dependence on the Ni concentration. The effective spin-mixing conductance of 8.40 × 1014 Ω−1 ⋅ m−2 and the interfacial spin transparency T in of 0.59 were obtained for the sample of Pt70Ni30/NiFe bilayer. More interestingly, the SOT efficiency that is carefully extracted from the angular dependence of ST-FMR spectra shows a nonmonotonic dependence on the Ni concentration, which reaches the maximum at x = 18. The enhancement of the SOT efficiency by alloying the Ni with Pt shows potential in lowering the critical switching current. Moreover, alloying relatively cheaper Ni with Pt may promote to reduce the cost of SOT devices.