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We report the tuneable spin angular momentum transfer (spin pumping) from Co60Fe20B20 (CFB) amorphous alloy into the Ta heavy metal nanolayers. All the films are grown on Si (100) substrate at room temperature using ion-beam sputtering technique. Structural studies reveal that the grown Ta films over amorphous CFB are crystalline even at ultrathin regime. The bilayers possess very low interface roughness (i.e., follows ballistic spin transport) in two series of CFB (4nm)/Ta (0-10nm) and CFB(6nm)/Ta (0-10nm) bilayers, which is characteristic of normal spin pumping. However, the anomalous behaviour has been observed for CFB (8nm)/Ta (0-10nm) bilayer series where the spin current generated in Ta with the thicker CFB behaves oppositely. The results demonstrate the strong dependence of ferromagnet thickness on the spin pumping into the Ta nanolayers. This study paves the way to choose suitable ferromagnetic layer thickness for spin current induced switching applications in spintronics.

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.

Ferromagnetic materials dominate as the magnetically active element in spintronic devices, but come with drawbacks such as large stray fields, and low operational frequencies. Compensated ferrimagnets provide an alternative as they combine the ultrafast magnetization dynamics of antiferromagnets with a ferromagnet-like spin-orbit-torque (SOT) behavior. However to use ferrimagnets in spintronic devices their advantageous properties must be retained also in ultrathin films (t < 10 nm). In this study, ferrimagnetic Gdx(Fe87.5Co12.5)1-x thin films in the thickness range t = 2-20 nm were grown on high resistance Si(100) substrates and studied using broadband ferromagnetic resonance measurements at room temperature. By tuning their stoichiometry, a nearly compensated behavior is observed in 2 nm Gdx(Fe87.5Co12.5)1-x ultrathin films for the first time, with an effective magnetization of Meff = 0.02 T and a low effective Gilbert damping constant of {\alpha} = 0.0078, comparable to the lowest values reported so far in 30 nm films. These results show great promise for the development of ultrafast and energy efficient ferrimagnetic spintronic devices., Comment: 7 Pages, 4 Figures

We report on the anisotropy of the effective damping (αeff) in the sputtered β-Ta(6 nm)/2D-epitaxial-Py(tPy = 3–10 nm) bilayers. In-plane field orientation dependent FMR measurements revealed a prominent anisotropy in αeff, which is ascribed to the spin wave induced spin pumping from Py to β-Ta in β-Ta/epi-Py system. The results especially suggest that at lower tPy a relatively larger αeff and its anisotropic nature are present in β-Ta/epi-Py bilayers as compared to bare epi-Py, which are unlikely at higher tPy. This is possibly due to both spin pumping which stems from in-plane spin waves associated with two magnon scattering mechanism and interface induced anisotropy from heavy metals like β-Ta at β-Ta/Py interface. The in-plane Hr vs. φ reveals clear anisotropy behavior at tPy ≤ 4 nm.

For achieving ultrafast switching speed and minimizing dissipation losses, the spin-based data storage device requires a control on effective damping (αeff) of nanomagnetic bits. Incorporation of interfacial antidamping spin orbit torque (SOT) in spintronic devices therefore has high prospects for enhancing their performance efficiency. Clear evidence of such an interfacial antidamping is found in Al capped Py(15 nm)/β-W(tW)/Si (Py = Ni81Fe19 and tW = thickness of β-W), which is in contrast to the increase of αeff (i.e., damping) usually associated with spin pumping as seen in Py(15 nm)/β-W(tW)/Si system. Because of spin pumping, the interfacial spin mixing conductance (g↑↓) at Py/β-W interface and spin diffusion length (λSD) of β-W are found to be 1.63(±0.02) × 1018 m–2 (1.44(±0.02) × 1018 m–2) and 1.42(±0.19) nm (1.00(±0.10) nm) for Py(15 nm)/β-W(tW)/Si (β-W(tW)/Py(15 nm)/Si) bilayer systems. Other different nonmagnetic capping layers (CL), namely, β-W(2 nm), Cu(2 nm), and β-Ta(2,3,4 nm) were also grown...

Structural and dynamic magnetization properties of Co2MnAl (CMA) full Heusler alloy thin films grown on Si (100) substrate at different substrate temperatures (Ts) 30°C, 200°C, 300°C, 400°C and 500°C are investigated. XRD patterns revealed the formation of B2 partially ordered phase at Ts=200°C and above. Ferromagnetic Resonance (FMR) technique have been used to determine the damping constant (α), resonance field (Hr) and line width (ΔH) of recorded spectra and fitted by using Landau-Lifshitz-Gilbert (LLG) equation. The lowest damping constant was found to be 0.007±0.002 for the film grown at Ts=200°C. Films exhibit uniaxial magnetic anisotropy. Anisotropic damping constant α is calculated along the easy and hard axis. Along the two directions remarkable change (almost ∼59%) in α is observed.

We have deposited polycrystalline Re doped $(Fe_{65}Co_{35})_{100-x}Re_{x}$ (0 $\leq$ x $\leq$ 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 found evidence of an increase in the real part of effective spin mixing conductance [Re($g^{\uparrow\downarrow}_{eff}$)] with the increase in Re doping of 6.6 at\%, while a decrease is evident at higher Re doping. The increase in Re($g^{\uparrow\downarrow}_{eff}$) can be linked to the Re doping induced change of the interface electronic structure in the non-magnetic Ru layer and the effect interfacial spin-orbit coupling has on the effective spin-mixing conductance. The lowest and highest values of Re($g^{\uparrow\downarrow}_{eff}$) are found to be 9.883(02) $nm^{-2}$ and 19.697(02) $nm^{-2}$ for 0 at\% and 6.6 at\% Re doping, respectively. The saturation magnetization decreases with increasing Re doping, from 2.362(13) T for the undoped film to 1.740(03) T for 12.6 at\% Re doping. This study opens a new direction of tuning the spin-mixing conductance in magnetic heterostructures by doping of the ferromagnetic layerr, which is essential for the realization of energy efficient operation of spintronic devices.

The Heusler ferromagnetic (FM) compound $\mathrm{C}{\mathrm{o}}_{2}\mathrm{FeAl}$ 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 $\mathrm{C}{\mathrm{o}}_{2}\mathrm{FeAl}/\ensuremath{\beta}$-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 $3.40\ifmmode\pm\else\textpm\fi{}0.01\ifmmode\times\else\texttimes\fi{}{10}^{19}\phantom{\rule{4pt}{0ex}}{\mathrm{m}}^{\ensuremath{-}2}$, $0.029\ifmmode\pm\else\textpm\fi{}0.003$, and $2.3\ifmmode\pm\else\textpm\fi{}0.5\phantom{\rule{4pt}{0ex}}\mathrm{nm}$, respectively. Furthermore, a high current modulation of the effective damping of around $2.1%$ has been achieved at an applied current density of $1\ifmmode\times\else\texttimes\fi{}{10}^{9}\mathrm{A}/{\mathrm{m}}^{2}$, which clearly indicates the potential of using this heterostructure for energy-efficient control in spin devices.

Spin-orbit torques in ferromagnetic (FM)/non-magnetic (NM) heterostructures offer more energy-efficient means to realize spin-logic devices; however, their strengths are determined by the heterostructure interface. This work examines crystal orientation impact on the spin-orbit torque efficiency in different Fe/Pd bilayer systems. Spin torque ferromagnetic 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., 8 Pages, 4 figures, 1 Table, epitaxial heterostructures for spin-oscillators

The effects of rhenium doping in the range 0 to 10 atomic percent on the static and dynamic magnetic properties of Fe65Co35 thin films have been studied experimentally as well as with first principles electronic structure calculations focusing on the change of the saturation magnetization and the Gilbert damping parameter. Both experimental and theoretical results show that the saturation magnetization decreases with increasing Re doping level, while at the same time Gilbert damping parameter increases. The experimental low temperature saturation magnetic induction exhibits a 29 percent decrease, from 2.31 T to 1.64 T, in the investigated doping concentration range, which is more than predicted by the theoretical calculations. The room temperature value of the damping parameter obtained from ferromagnetic resonance measurements, correcting for extrinsic contributions to the damping, is for the undoped sample 0.0027, which is close to the theoretically calculated Gilbert damping parameter. With 10 atomic percent Re doping, the damping parameter increases to 0.0090, which is in good agreement with the theoretical value of 0.0073. The increase in damping parameter with Re doping is explained by the increase in density of states at Fermi level, mostly contributed by the spin-up channel of Re. Moreover, both experimental and theoretical values for the damping parameter are observed to be weakly decreasing with decreasing temperature., 13 pages, 8 figures, 5 tables, Materials for spin-logic circuits

We correlate the structural, electrical, and magnetotransport properties of co-sputtered Mn2-xCo1+xAl full Heusler alloy thin films (0 ≤ x ≤ 1.75) in terms of Co/Mn concentration variation concerning the spin gapless semiconducting (SGS) behavior. The alloy thin films are found to stabilize in B2 order for near stoichiometric films, i.e. (x = 0 and x = 1), with the gradual change in the ordering and lattice parameter through Mn concentration variation. Magnetization measurements in Mn2-xCo1+xAl thin films reveal the ferromagnetic and ferrimagnetic character for x = 1.75, 1.5, 1.25 & 1, and x = 0, 0.5 & 0.75, respectively. The longitudinal resistivity measurement revealed that the films exhibit semiconducting behavior with a change in sign of the temperature coefficient of resistance with temperature. The anomalous Hall conductivity values for the Mn2-xCo1+xAl thin films are extracted from the Anomalous Hall effect (AHE) measurements. The non-saturating positive MR (linear in H) is being reported for the first time in the Mn2CoAl thin films. The value of the AHE coefficient and positive MR together serve as a piece of experimental evidence for the SGS character in the thin film. The SGS behavior becomes predominant at higher Mn concentration. Highly resistive thin films with ferromagnetic (ferrimagnetic) character in Co2MnAl (Mn2CoAl) could be beneficial for semiconductor spintronics, where we need a good resistive element to match up with Silicon base substrate.

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.

We report the systematic dependence of spin pumping in tungsten (W)/CoFeB heterostructures on the structural phase of W, which is intricately related to argon gas pressure (${p}_{\mathrm{Ar}}$) maintained during the sputter deposition. We found that with increasing ${p}_{\mathrm{Ar}}$ the structural phase of W changes from mixed ($\ensuremath{\alpha}+\ensuremath{\beta}$) phase to pure $\ensuremath{\beta}$ phase. The $\ensuremath{\beta}$-W is stabilized in films for the high thickness of 40 nm which is desirable for spin devices. Using ferromagnetic resonance measurement of W(${p}_{\mathrm{Ar}}$)/CoFeB heterostructures, it is shown that enhancement of magnetic damping (${\ensuremath{\alpha}}_{\mathrm{eff}}$) from spin pumping is more in $\ensuremath{\beta}$-W compared to ($\ensuremath{\alpha}+\ensuremath{\beta}$)-W. The effective spin mixing conductance (${g}_{\mathrm{eff}}^{\ensuremath{\uparrow}\ensuremath{\downarrow}}$) is estimated for different phases of W from the linear evolution of ${\ensuremath{\alpha}}_{\mathrm{eff}}$ with the inverse thickness of the CoFeB layer. For $\ensuremath{\beta}$-W, the ${g}_{\mathrm{eff}}^{\ensuremath{\uparrow}\ensuremath{\downarrow}}$ is found to be larger than that of ($\ensuremath{\alpha}+\ensuremath{\beta}$)-W and it is attributed to different interface structure. Thus, effective tuning of spin pumping efficiency can be achieved using different W crystal phases. We also studied the dependence of ${\ensuremath{\alpha}}_{\mathrm{eff}}$ on $\ensuremath{\beta}$-W film thickness to calculate the value of spin-diffusion length (${\ensuremath{\lambda}}_{\mathrm{SD}}$) and intrinsic spin mixing conductance (${g}_{\ensuremath{\beta}\text{\ensuremath{-}}W}^{\ensuremath{\uparrow}\ensuremath{\downarrow}}$) using both the ballistic and diffusive spin transport models.

Spin pumping from the full Heusler alloy $\mathrm{C}{\mathrm{o}}_{2}\mathrm{FeAl}$ film into the transition-metal dichalcogenide $\mathrm{Mo}{\mathrm{S}}_{2}$ is reported. Plasma-assisted sulfurization of ion-beam sputtered Mo films of different nominal thicknesses is employed to first fabricate large area high-quality $\mathrm{Mo}{\mathrm{S}}_{2}$ sheets [thicknesses: 1, 2, 3, and 4 monolayers (MLs)] on $\mathrm{Si}{\mathrm{O}}_{2}/\mathrm{Si}$ substrates, followed by deposition of $\mathrm{C}{\mathrm{o}}_{2}\mathrm{FeAl}$ films with a fixed thickness of 8 nm. The spin pumping is investigated by measuring the changes in the damping constant in the Al(5 nm) capped $\mathrm{C}{\mathrm{o}}_{2}\mathrm{FeAl}/\mathrm{Mo}{\mathrm{S}}_{2}$ bilayers using ferromagnetic resonance spectroscopy. The study demonstrates that even 1 ML of $\mathrm{Mo}{\mathrm{S}}_{2}$ possesses high enough spin-orbit coupling strength to enhance damping from $5.5(\ifmmode\pm\else\textpm\fi{}0.2)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ in $\mathrm{Al}(5\phantom{\rule{0.16em}{0ex}}\mathrm{nm})/\mathrm{C}{\mathrm{o}}_{2}\mathrm{FeAl}(8\phantom{\rule{0.16em}{0ex}}\mathrm{nm})$ to a nearly saturated value of $8.3(\ifmmode\pm\else\textpm\fi{}0.2)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ in $\mathrm{Al}(5\phantom{\rule{0.16em}{0ex}}\mathrm{nm})/\mathrm{C}{\mathrm{o}}_{2}\mathrm{FeAl}(8\phantom{\rule{0.16em}{0ex}}\mathrm{nm})/\mathrm{Mo}{\mathrm{S}}_{2}(1\phantom{\rule{0.16em}{0ex}}\mathrm{ML})$, which is suppressed by inserting a thin Al layer at the $\mathrm{C}{\mathrm{o}}_{2}\mathrm{FeAl}/\mathrm{Mo}{\mathrm{S}}_{2}$ interface. The observed enhancement in damping is in agreement with the results from first-principles calculations based on density functional theory. These results open up a paradigm for designing spintronic devices based on heterostructures comprising a full Heusler alloy and the inherently stable $\mathrm{Mo}{\mathrm{S}}_{2}$.

In the present work Co2FeAl (CFA) thin films were deposited by ion beam sputtering on Si (100) substrates at the optimized deposition temperature of 300°C. A series of CFA films with different thic ...

The spin-pumping mechanism and associated interfacial Gilbert damping are demonstrated in ion-beam sputtered Co2FeAl (CFA)/Mo bilayer thin films employing ferromagnetic resonance spectroscopy. The ...

Mn56Al44 (MnAl) thin films of constant thickness (∼30nm) were grown on naturally oxidized Si substrates using DC-magnetron sputtering. Effect of deposition parameters such as sputtering power, substrate temperature (Ts), and post-annealing temperature have been systematically invstigated. X-ray diffraction patterns revealed the presence of mixed phases, namely the τ- and β-MnAl. The highest saturation magnetization (MS) was found to be 65emu/cc using PPMS-VSM in film grown at Ts=500°C. The magnetic ordering was found to get significantly improved by performing post-annealing of these as-grwon at 400°C for 1 hr in the presence of out-of-plane magnetic field of ∼1500Oe in vacuum. In particular, at room temperature (RT), the MS got enhanced after magnetic annealing from 65emu/cc to 500 emu/cc in MnAl films grown at Ts=500°C. This sample exhibited a magneto-resistance of ∼1.5% at RT. The tuning of the structural and magnetic properties of MnAl binary alloy thin films as established here by varying the growth parameters is critical with regards to the prospective applications of MnAl, a metastable ferromagnetic system which possesses the highest perpendicular magnetic anisotropy at RT till date.Mn56Al44 (MnAl) thin films of constant thickness (∼30nm) were grown on naturally oxidized Si substrates using DC-magnetron sputtering. Effect of deposition parameters such as sputtering power, substrate temperature (Ts), and post-annealing temperature have been systematically invstigated. X-ray diffraction patterns revealed the presence of mixed phases, namely the τ- and β-MnAl. The highest saturation magnetization (MS) was found to be 65emu/cc using PPMS-VSM in film grown at Ts=500°C. The magnetic ordering was found to get significantly improved by performing post-annealing of these as-grwon at 400°C for 1 hr in the presence of out-of-plane magnetic field of ∼1500Oe in vacuum. In particular, at room temperature (RT), the MS got enhanced after magnetic annealing from 65emu/cc to 500 emu/cc in MnAl films grown at Ts=500°C. This sample exhibited a magneto-resistance of ∼1.5% at RT. The tuning of the structural and magnetic properties of MnAl binary alloy thin films as established here by varying the growth ...

Structural and dynamic magnetization properties of Co2MnAl (CMA) full Heusler alloy thin films grown on Si(100) substrates at different substrate temperatures (Ts) room temperature (RT), 200°C, 300°C, 400°C and 500°C are investigated. X-ray diffraction patterns revealed the formation of B2 ordered phase. Ferromagnetic Resonance (FMR) technique have been used to investigate the dynamic magnetization response. From the observed frequency dependence of the resonance field (Hr) and line width (ΔH), the effective saturation magnetization (4πMeff) and damping constant (α) have been evaluated. The lowest damping constant was found to be 0.007±0.002 for the film grown at Ts=200°C which is comparable to the reported value.

Co2FeAl (CFA) thin films of 50 nm thickness have been grown on MgO (0 0 1) single crystal substrates at room temperature with and without post-annealing (PA) at 300 °C and 400 °C using dual ion-beam sputtering technique. The XRD pattern of the as-grown film revealed that CFA grows with preferred crystallographic orientation on the MgO (0 0 1) substrate. Temperature dependent anisotropy measurements on PA films revealed a dominating contribution from cubic anisotropy as confirmed by the analysis of azimuthal angle dependent longitudinal in-plane magneto-optical Kerr effect (MOKE) measurements. The contributions from the cubic and uniaxial anisotropies have also been quantified employing ferromagnetic resonance spectroscopy. Magnetization reversal is accompanied with a plateau in the MOKE hysteresis recorded at various azimuthal angles in the in-plane applied magnetic field configuration. The occurrence of the observed plateau is explained by the presence of a combination of domain walls such as 90°, 135° and 180° domain walls and/or complex domains which is supported by results from micromagnetic simulations. These results demonstrate the feasibility of manipulating the magnetization switching in one of the two ferromagnetic electrodes of the magnetic tunnel junction devices based on Heusler alloy ferromagnetic films.

The structure, electrical and magnetic transport properties of cobalt nanoparticles having core–shell structure are presented. The nanoparticles were prepared by a borohydride reduction method followed by heat treatments. X-ray diffraction shows that the as-prepared samples are amorphous while annealed samples are crystalline having a majority of fcc-Co along with metastable Co 3 B. The particles are spherical in shape and the average grain size increases with increasing anneal temperature. The core–shell structure is confirmed by high resolution transmission electron microscopy. The structural study reveals that the cores of the as-prepared and the annealed samples are of fcc-Co, while there is a profound microstructural change of the shells with annealing. A large change in the resistivity is observed between the as-prepared and annealed samples. The electrical transport properties at low temperature are interpreted in terms of tunneling between ferromagnetic cobalt cores through the non-magnetic shell. Improvements of the magnetic and the transport properties of the nanoparticles with annealing are observed with microstructural changes of the core–shell structure. The saturation magnetization ( M s =40 emu/g) at room temperature suggests that air annealed (500 °C) samples are protected from oxidation due to the formation of a B 2 O 3 protective layer. These results suggest that this kind of nanocomposite systems might have significant potentiality in recording media and in medical diagnostic or therapy applications.

The influence of MgO and Ta capping layers on the static and dynamic magnetic properties of Co2FeAl (CFA) Heusler alloy thin films has been investigated. It is observed that the CFA film deposited ...

The prime requirements for the spin transfer torque based ferromagnetic (FM)/nonmagnetic (NM) bilayer spin devices are (i) the absence of two-magnon scattering (TMS) noise, (ii) minimum energy dissipation and (iii) fast switching. To realize these objectives we have studied the thickness, Py (permalloy) thicknesses (t(Py)) and beta-Ta thicknesses (t(Ta)), dependent magnetization dynamics behaviour of the epitaxial Py (t(Py) = 3-20 nm)/beta-Ta (t(Ta) = 1.5-15 nm) system. The t(Py) dependence of TMS in epitaxial Py nanolayers (t(Py) = 3-20 nm) grown on a Si(400)/TiN(200) (8 nm) substrate is explored in terms of uniform and non-uniform magnetization precession regimes by employing ferromagnetic resonance field (H-r), linewidth (Delta H), and Gilbert damping constant (alpha) behaviour. It is found that in Py, t(Py) < 10 nm, layers TMS is dominating due to non-uniform precession of the magnetization. However in Py, t(Py) >= 10 nm, layers the uniform magnetization precession dominates, therefore Py layers, t(Py) >= 10 nm, are almost free from TMS. Furthermore, a nearly TMS free 12 nm epitaxial Py(200) layer is capped with beta-Ta (t(Ta) = 1.5-15 nm) layers to explore the t(Ta) dependent magnetization precession of epitaxial Py (12 nm) in terms of change in effective Gilbert damping constant (alpha(eff)). An anomalous decrease in alpha(eff) from 0.0087 at t(Ta) = 0 to a minimum value of 0.0077 at t(Ta) = 6 nm, and its subsequent increase for t(Ta) > 6 nm are observed in the epitaxial Py (12 nm)/beta-Ta(t(Ta)) system. Therefore the Si(400)/TiN(200) (8 nm)/Py(200) (12 nm)/beta-Ta(200) (6 nm) epitaxial system with nearly uniform magnetic precession and minimum effective Gilbert damping is suitable for low energy loss and ultrafast switching applications in spin transfer torque devices.

The pulse DC sputtered nanostructured Fe3O4 thin films have been subjected to hydrocarbon treatment and vacuum annealing to investigate their effect on grain boundaries. Remarkably, this treatment causes a change in the crystallographic structure of the film from polycrystalline to (440) oriented one and enhancement in film conductivity. Hopping conduction mechanism changes to nearest-neighbor hoping above Verwey transition temperature of 110 K on treatment. Treatment also leads to grain boundary modification by incorporation of antiferro defects that inhibit an increase in MR despite enhanced electron conduction across grain boundaries. Our results follow the non-homogeneous grain boundary model.

Anomalous decrease in effective damping parameter αeff in sputtered Ni81Fe19 (Py) thin films in contact with a very thin β-Ta layer without necessitating the flow of DC-current is observed. This reduction in αeff, which is also referred to as anti-damping effect, is found to be critically dependent on the thickness of β-Ta layer; αeff being highest, i.e., 0.0093 ± 0.0003 for bare Ni81Fe19(18 nm)/SiO2/Si compared to the smallest value of 0.0077 ± 0.0001 for β-Ta(6 nm)/Py(18 nm)/SiO2/Si. This anomalous anti-damping effect is understood in terms of interfacial Rashba effect associated with the formation of a thin protective Ta2O5 barrier layer and also the spin pumping induced non-equilibrium diffusive spin-accumulation effect in β-Ta layer near the Ta/Py interface which induces additional spin orbit torque (SOT) on the moments in Py leading to reduction in "Equation missing". The fitting of "Equation missing" (tTa) revealed an anomalous negative interfacial spin mixing conductance, "Equation missing"and spin diffusion length,"Equation missing". The increase in αeff observed above tTa = 6 nm is attributed to the weakening of SOT at higher tTa. The study highlights the potential of employing β-Ta based nanostructures in developing low power spintronic devices having tunable as well as low value of α.

Angular dependent magnetization reversal has been investigated in Co2MnAl (CMA) full Heusler alloy thin films grown on Si(100) at different growth temperatures (Ts) by DC-magnetron sputtering. An M-shaped curve is observed in the in-plane angular (0°–360°) dependent coercivity (ADC) by magneto-optical Kerr effect measurements. The dependence of the magnetization reversal on Ts is investigated in detail to bring out the structure-property correlation with regards to ADC in these polycrystalline CMA thin films. This magnetization reversal ( M-shaped ADC behavior) is well described by the two-phase model, which is a combination of Kondorsky (domain wall motion) and Stoner Wohlfarth (coherent rotation) models. In this model, magnetization reversal starts with depinning of domain walls, with their gradual displacement explained by the Kondorsky model, and at a higher field (when the domain walls merge), the system follows coherent rotation before reaching its saturation following the Stoner Wohlfarth model. Fu...

We perform spin torque ferromagnetic resonance measurements on the Si(100)/TiN(100)/epi-Py(100)/β-Ta system. We demonstrate current induced modulation of the Gilbert damping constant, which is about 30% for a current density of 6.25 × 109 A/m2. We show that the observed modulation of the Gilbert damping constant cannot be explained by spin transfer torques arising from the spin Hall effect of the β-Ta layer. An additional mechanism such as antidamping spin-orbit torque resulting from the interface or the crystalline structure of Py thin films needs to be considered.

We report on the optical detection of the spin Hall effect (SHE) as a function of the crystalline structure of sputtered Ta thin films using a magneto-optical Kerr system. The growth rate of Ta films is found to influence the crystalline phase of Ta films. At a lower growth rate, GR the pure α-phase of Ta is formed, which changes to the pure β-phase for GR ≥ 1.44 A/s. For an intermediate growth rate, 0.62 A/s ≤ GR

Broadband in-plane ferromagnetic resonance was performed in Ta/Ni81Fe19 (Py) bilayer nanostructure in which the thickness of both Ta and Py layers has been varied in the range comparable to spin diffusion length λSD of normal metal. The ratio of symmetric Lorentzian to anti-symmetric Lorentzian peaks decreases from 12.22 to 1.28. We have shown that both Spin Hall Effect and spin pumping increase and total Gilbert damping constant α increases with decrease in thickness of bilayer.

We report an investigation of the non-linear electrical transport and magnetic transport properties associated with Co/CoO core-shell nanoparticles, over the temperature range 10-300 K. Nanoparticle of size 60-70 nm was synthesized by borohydride reduction technique where the core-shell structure is confirmed by the high resolution Transmission Electron Microscopy. The resistivity was found to vary almost linearly with temperature showing a normal metallic behavior with a residual resistivity of 30μΩ-m. The nonlinear electric transport is observed at temperatures (T) below 300 K and is explained using the Glazman and Matveev model. The nanoparticles showed negative Magnetoresistance (MR), in the range 0.25-2.3% on application of magnetic field parallel and perpendicular to the direction of current flow. This change in magnetoristance is observed to have close relation to the nonlinear electrical transport within the Co/CoO nanoparticles.

We report the effect of Ru thickness (tRu) on ferromagnetic resonance (FMR) line-width of Ru(tRu)/Py(23 nm) bilayer samples grown on Si(100)/SiO2 substrates at room temperature by magnetron sputtering. The FMR line-width is found to vary linearly with frequency for all thicknesses of Ru, indicating intrinsic origin of damping. For Ru thicknesses below 15 nm, Gilbert-damping parameter, α is almost constant. We ascribe this behavior to spin back flow that is operative for Ru thicknesses lower than the spin diffusion length in Ru, λsd. For thicknesses >15 nm (>λsd), the damping constant increases with Ru thickness, indicating spin pumping from Py into Ru.

The interface roughness, Boron distribution in bulk CoFeB and at interface, Gilbert damping constant (α), and inhomogeneous broadening in ion-beam sputtered Si/CoFeB(8)/MgO(4)/CoFeB(8)/Ta(5) structures are found to be sensitive to the MgO growth process. The ion-assist and reactive growth processes that result in sharper interfaces of width ∼0.5 nm lead to smaller α of 0.0050 ± 0.0003 and 0.0060 ± 0.0002 and inhomogeneous broadening ΔH0 of 3 ± 0.3 and 1 ± 0.3 Oe, respectively. On the other hand, the post-oxidation method results in rough interface and higher retention of Boron in CoFeB leading to higher values for α and ΔH0 as 0.0080 ± 0.0006 and 5 ± 0.3 Oe, respectively.