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Fe₆₅Co₃₅ thin films have been deposited on SiO₂ substrates using sputtering technique with different choices of seed layer; Ru, Ni_82.5Fe_17.5, Rh, Y and Zr. Best soft magnetic properties were observed with seed layers of Ru, Ni_82.5Fe_17.5 and Rh. Adding these seed layers, the coercivity of the Fe₆₅Co₃₅ films decreased to values of around 1.5 mT, which can be compared to the value of 12.5 mT obtained for films deposited without seed layer. Further investigations were performed on samples with these three seed layers in terms of dynamic magnetic properties, both on as prepared and annealed samples, using constant frequency cavity and broadband ferromagnetic resonance measurements. Damping parameters of around 8.0X10^-3 and 4.5X10^-3 were obtained from in-plane and out-of-plane measurements, respectively, for as prepared samples, values that were reduced to 6.5X10^-3 and 4.0X10^-3 for annealed samples.

We have deposited polycrystalline Re-doped (Fe₆₅Co₃₅)(_100-x)Re_x (0 ≤ x ≤ 12.6 at. %) thin films grown under identical conditions and sandwiched between thin layers of Ru in order to study the phenomenon of spin pumping as a function of Re concentration. In-plane and out-of-plane ferromagnetic resonance spectroscopy results show an enhancement of the Gilbert damping with an increase in Re doping. We find 98% enhancement in the real part of effective spin mixing conductance [Re(g^↑↓_eff)] with Re doping. Conversely, the Re(g^↑↓_eff) does not change with Re doping in Fe₆₅Co₃₅ thin films which are seeded and capped with Cu layers. The enhancement in Re(g^↑↓_eff) of Re-doped Fe₆₅Co₃₅ thin films sandwiched between thin layers of Ru is linked to the Re doping-induced change of the interface electronic structure in the nonmagnetic Ru layer. The saturation magnetization decreases 35% with increasing Re doping up to 12.6 at. %. This study opens a direction of tuning the spin mixing conductance in magnetic heterostructures by doping of the ferromagnetic layer, which is essential for the realization of energyefficient operation of spintronic devices.

We report on optically induced, ultrafast magnetization dynamics in the Heusler alloy Co2FeAl, probed by time-resolved magneto-optical Kerr effect. Experimental results are compared to results from electronic structure theory and atomistic spin-dynamics simulations. Experimentally, we find that the demagnetization time (tau(M)) in films of Co2FeAl is almost independent of varying structural order, and that it is similar to that in elemental 3d ferromagnets. In contrast, the slower process of magnetization recovery, specified by tau(R), is found to occur on picosecond time scales, and is demonstrated to correlate strongly with the Gilbert damping parameter (alpha). Based on these results we argue that for Co2FeAl the remagnetization process is dominated by magnon dynamics, something which might have general applicability.

The Heusler ferromagnetic (FM) compound Co2FeAl interfaced with a high spin-orbit coupling nonmagnetic (NM) layer is a promising candidate for energy-efficient spin-logic circuits. The circuit potential depends on the strength of angular momentum transfer across the FM/NM interface, hence requiring low spin-memory loss and high spin-mixing conductance. To highlight this issue, spin pumping and spin torque ferromagnetic resonance measurements have been performed on Co2FeAl/beta-Ta heterostructures tailored with Cu interfacial layers. The interface tailored structure yields an enhancement of the effective spin-mixing conductance. The interface transparency and spin-memory loss corrected values of the spin-mixing conductance, spin Hall angle, and spin-diffusion length are found to be 3.40 +/- 0.01x10(19) m(-2), 0.029 +/- 0.003, and 2.3 +/- 0.5 nm, respectively. Furthermore, a high current modulation of the effective damping of around 2.1% has been achieved at an applied current density of 1 x 10(9)A/m(2), which clearly indicates the potential of using this heterostructure for energy-efficient control in spin devices.

Spin-orbit torques in ferromagnetic/non-magnetic heterostructures offer more energy-efficient means to realize spin-logic devices; however, their strengths are determined by the heterostructure interface. This work examines the impact of crystal orientation on the spin-orbit torque efficiency in different Fe/Pd bilayer systems. Results from spin torque ferromagnetic resonance measurements evidence that the damping-like torque efficiency is higher in epitaxial than in polycrystalline bilayer structures while the field-like torque is negligible in all bilayer structures. The strength of the damping-like torque decreases with deterioration of the bilayer epitaxial quality. The present finding provides fresh insight for the enhancement of spin-orbit torques in magnetic heterostructures.

Spin-orbit coupling (SOC) in two-dimensional (2D) materials has emerged as a powerful tool for designing spintronic devices. On the one hand, the interest in this respect for graphene, the most popular 2D material with numerous fascinating and exciting properties, is fading due to the absence of SOC. On the other hand, 2D transition metal dichalcogenides (TMDs) are known to exhibit rich physics including large SOC. TMDs have been used for decades in a variety of applications such as nano-electronics, photonics, optoelectronics, sensing, and recently also in spintronics. Here, we review the current progress in research on 2D TMDs for generating spin-orbit torques in spin-logic devices. Several challenges connecting to thin film growth, film thickness, layer symmetry, and transport properties and their impact on the efficiency of spintronic devices are reviewed. How different TMDs generate spin-orbit torques in magnetic heterostructures is discussed in detail. Relevant aspects for improving the quality of the thin film growth as well as the efficiency of the generated spin-orbit torques are discussed together with future perspectives in the field of spin-orbitronics.

A damping-like spin-orbit torque (SOT) is a prerequisite for ultralow-power spin logic devices. Here, we report on the damping-like SOT in just one monolayer of the conducting transition-metal dichalcogenide (TMD) TaS2 interfaced with a NiFe (Py) ferromagnetic layer. The charge-spin conversion efficiency is found to be 0.25 +/- 0.03 in TaS2(0.88)/Py(7), and the spin Hall conductivity (14.9 x 10(s) h/2e Omega(-1) m(-1) is found to be superior to values reported for other TMDs. We also observed sizable field-like torque in this heterostructure. The origin of this large damping-like SOT can be found in the interfacial properties of the TaS2/Py heterostructure, and the experimental findings are complemented by the results from density functional theory calculations. It is envisioned that the interplay between interfacial spinorbit coupling and crystal symmetry yielding large damping-like SOT. The dominance of damping-like torque demonstrated in our study provides a promising path for designing the next-generation conducting TMD-based low-powered quantum memory devices.

Spin-based terahertz (THz) emitters, utilizing the inverse spin Hall effect, are ultra-modern sources for the generation of THz electromagnetic radiation. To make a powerful emitter having large THz amplitude and bandwidth, fundamental understanding in terms of microscopic models is essential. This study reveals important factors to engineer the THzemission amplitude and bandwidth in epitaxial Pt/Fe emitters grown on MgO and MgAl₂O₄ (MAO) substrates, where the choice of the substrate plays an important role. The THz amplitude and bandwidth are affected by the induced strain in the Fe spin source layer. On the one hand, the THz electric field amplitude is found to be larger when Pt/Fe is grown on MgO even though the crystalline quality of the Fe film is superior when grown on MAO. This is because of the larger defect density, smaller electron relaxation time, and lower electrical conductivity in the THz regime when Fe is grown on MgO. On the other hand, the bandwidth is found to be larger for Pt/Fe grown on MAO and is explained by the uncoupled/coupled Lorentz oscillator models. This study provides an insightful pathway to further engineer metallic spintronic THz emitters in terms of the proper choice of substrate and microscopic properties of the emitter layers. 

The choice of the substrate plays an important role for spintronic terahertz (THz) emitters (STEs). We have grown epitaxial Pt/Fe bilayer thin films on MgO and MgAl₂O₄ substrates. The THz electric field amplitude is found to be larger when Pt/Feis is grown on MgO even though the crystal quality of the Fe film is better when grown on MgAl2O4. This study indicates that the Fecrystal quality affects the THz emission in Pt/Fe STEs and points to the importance of a careful choice of the substrate to enhance the THz amplitude in STEs.

To achieve a large terahertz (THz) amplitude from a spintronic THz emitter (STE), materials with 100% spin polarisation such as Co-based Heusler compounds as ferromagnetic layer are required. However, these compounds are known to loose their half-metallicity in the ultrathin film regime, as it is difficult to achieve L2(1) ordering, which has become a bottleneck for the film growth. Here, the successful deposition using room temperature DC sputtering of the L2(1) and B2 ordered phases of the Co2FeAl full Heusler compound is reported. Co2FeAl is used as ferromagnetic layer together with highly orientated Pt as nonferromagnetic layer in the Co2FeAl/Pt STE, where an MgO (10 nm) seed layer plays an important role to achieve the L2(1) and B2 ordering of Co2FeAl. The THz generation in the Co2FeAl/Pt STE is presented, which has a bandwidth of 0.2-4 THz. The THz electric field amplitude is optimized with respect to thickness, orientation, and growth parameters using a thickness dependent model considering the optically induced spin current, superdiffusive spin current, inverse spin Hall effect, and the THz attenuation in the layers. This study, based on the full Heusler Co2FeAl compound opens up a plethora of possibilities in STE research involving full Heusler compounds.