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Topological insulators (TIs) are the promising materials for next-generation technology due to their exotic features such as spin momentum locking, conducting surface states, etc. However, the high-quality growth of TIs by sputtering technique, which is one of the foremost industrial requirements, is extremely challenging. Also, the demonstration of simple investigation protocols to characterize topological properties of TIs using electron-transport methods is highly desirable. Here, we report the quantitative investigation of non-trivial parameters employing magnetotransport measurements on a prototypical highly textured Bi2Te3 TI thin film prepared by sputtering. Through the systematic analyses of the temperature and magnetic field dependent resistivity, all topological parameters associated with TIs, such as coherency factor (α), Berry phase (Φ_B), mass term (m), the dephasing parameter (p), slope of temperature dependent conductivity correction (κ) and the surface state penetration depth (λ) are estimated by using the modified ‘Hikami-Larkin-Nagaoka’, ‘Lu-Shen’ and ‘Altshuler-Aronov’ models. The obtained values of topological parameters are well comparable to those reported on molecular beam epitaxy grown TIs. The epitaxial growth of Bi2Te3 film using sputtering, and investigation of the non-trivial topological states from its electron-transport behaviour are important for their fundamental understanding and technological applications.

Spin gapless semiconductors (SGSs) are an intriguing class of quantum materials that bridge the gap between half-metallic ferromagnets and semiconductors. The presence of a semiconducting bandgap for one spin channel and zero band gap for other spin channels, together with the possibility of four different band structure configurations, makes them one of the most desirable candidates to be used in tunable spin transport based spintronics devices. Here, we have performed various structural, magnetic and transport measurements on an optimized CoFeCrGa (CFCG) Heusler alloy thin film (∼50 nm) grown over a Si(100) substrate using an industry-viable magnetron sputtering technique. The grown film showed B2-ordering under the given set of X-ray diffraction measurement conditions with a saturation magnetization (

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.

Magnetoresistance (MR) in thin films stems from different types of scattering mechanism present in the film. We report a systematic study of the temperature-dependent magnetoresistance behaviour in the pulsed DC magnetron sputtered Ni81Fe19 thin film on Si (100). X-ray diffraction study reveals the polycrystalline nature of the film along with the presence of preferred orientation. X-ray reflectivity measurement shows very low interface roughness (0.55 ± 0.04 nm). Temperature-dependent resistivity measurement is performed over a temperature range of 25–300 K, unveiling the dominance of electron-magnon scattering and impurity scattering at lower temperature (25–250 K) and electron-phonon scattering at higher temperature (above 250 K). In the investigated temperature range (30–300 K), the MR magnitude is found to reduce from 0.97 to 0.51% with increment in measurement temperature from 30 to 300 K. This reduction is attributed to the enhancement in phonon scattering at higher temperatures, and relatively suppressed ordering influence of magnetic field at higher temperature due to higher thermal activation energy and impurity scattering.

The spin-pumping behavior in the as-deposited and post-deposition annealed (at 400 °C) Co60Fe20B20/Molybdenum (CoFeB/Mo) heterostructures is investigated. It is found that while in both the as-deposited and annealed CoFeB/Mo heterostructures, Mo crystallizes in the form of mixed phases, i.e., body centered cubic ( bcc) and face centered cubic ( fcc), the dominance, however, changes from fcc to bcc on annealing. The ferromagnetic resonance measurements reveal that despite relatively low spin orbit coupling of Mo, the spin-pumping efficiency and magnetic properties in both the as-deposited as well as in the annealed heterostructures was comparable with those reported in similar CoFeB based heterostructures comprising of other nonmagnetic metals such as W and Ta. The spin efficiency parameters are, however, slightly better when the Mo film is predominantly in the fcc phase as compared to the case when the Mo film dominantly comprises of the bcc phase. The different spin-pumping efficiencies in the two different combinations of phases of Mo are attributed to the different band structures and the density of states in different phases of Mo, as confirmed by density functional theory calculations. The slight changes observed in the spin-pumping response are possibly attributed to the structural manifestations that result at the interface that the two phases of Mo share with CoFeB. Importantly, despite the weak spin–orbit interaction, the 4 d transition metal Mo could be a suitable choice of non-magnetic material for spin pumping when the thermal stability of different layers in the CoFeB based spintronic devices is of paramount concern.

Effect of substrate rotation on the structural, magneto-optic and magneto-transport properties of DC magnetron sputtered Co60Fe40 thin films is investigated. Two thin film samples (each of 20 nm thickness) were prepared by rotating (S-WR) and without rotating (S-WOR) the substrate during deposition. X-ray diffraction (XRD) patterns reveal that the films exhibit textured crystallographic orientation. Surface morphological analysis of these films indicate that the surface of S-WR is smooth in comparison to the sample S-WOR. The magneto-optic Kerr effect analysis reveals that the sample S-WR is isotropic in nature whereas a large uniaxial anisotropy is present in the sample S-WOR due to textured orientation as supported by XRD study. The effect of rotation on the anisotropy is further demonstrated by measuring magneto-resistance (MR) in two configurations, i.e., longitudinal (LMR) and transverse magnetoresistance (TMR) configurations. In the sample S-WOR, the values of MR are quite different, i.e., 0.29% (TMR) and −0.10% (LMR) whereas identical MR values, i.e., 0.19% (for both LMR and TMR), were observed in the sample S-WR. This indicates that the anisotropy in CoFe can be suppressed by rotating the substrates during growth. Thus the tunability of anisotropy is possible by rotating the substrate which is potentially useful for manipulating the properties of ferromagnetic materials for spintronic applications.

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 (2 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.

We report an investigation of spin wave propagation in ion beam sputtered Co2FeAl Heusler alloy thin film on Si(100) substrate. The spin wave transmission spectra measured at fixed frequencies by sweeping the external applied magnetic field were used to estimate technologically relevant spin wave propagation parameters. The spin wave group velocity was found at 6.1 km s−1 with an attenuation length larger than 7 μm. The Gilbert damping parameter was estimated to be 0.019. The frequency dependency of the group velocity decreased with increasing frequency and the attenuation length increased at low frequencies while started to decrease at larger frequencies. The amplitude of non-reciprocity also decreased with increasing frequency. The propagation parameters presented were also independently verified by time-resolved propagating spin wave spectroscopy.

Spin gapless semiconducting (SGS) behaviour of polycrystalline CoFeMnSi (CFMS) Heusler alloy thin film was investigated through structural, magnetic, magnetotransport and electron-transport characterization. In this study, we have tailored the structural ordering in CFMS thin films (∼60 nm) grown at different substrate temperatures (TS) in 150°C to 550°C range on Si(100) substrates using pulsed DC magnetron sputtering. All the grown films were polycrystalline in nature, showing an enhancement in structural ordering with TS. Among all the samples, the film grown at 550°C showed an optimal structure with L21 ordering. The magnetic measurements revealed that saturation magnetization (Ms) of the sample decreased with the an increment in temperature with a value ∼3.42 μB/f.u. at 5K to 3.11 μB/f.u. at 300 K. The Curie temperature (TC) of the sample was estimated to be 778±13K. The longitudinal resistivity ( σ XX ) measurements clearly exhibited a negative temperature coefficient of resistivity, indicating the non-metallic behaviour of these CFMS films. The fitting of resistivity curve dig out contribution of electron-phonon scattering and defect scattering to resistivity. Fitting also suggest that holes are the majority charge carriers in optimized CFMS thin film which was further confirmed through positive slope of anomalous Hall resistivity (AHE) curve. The temperature-dependent anomalous Hall effect measurements have also been carried out to identify the different scattering mechanisms responsible for AHE. The results suggested that both the intrinsic as well as extrinsic factors contribute to the AHE of CFMS deposited film with non-zero contribution of phonon-related skew scattering. The carrier concentration (n) and mobility (μ) were found to be nearly temperature-independent, revealing typical SGS characteristics. At room temperature, the n and μ values were found to be 3.9±0.04 ×1021 cm-3 and 88.83±1.58 cm2/Vs, respectively. The value of anomalous Hall conductivity at 5K is found to be 53.79 S/cm. .

In this study, the development of uniaxial magnetic anisotropy (UMA) and out-of-plane coercivity (Hc┴) in W/Co20Fe60B20(CoFeB)/W structures by tuning the annealing temperature (TA) such as 300°C, 400°C and 500°C were achieved. For 400°C film, W and CoFeB interfaces play a major role in achieving the large Hc┴. Furthermore, the observation of large Hc┴ was found to be significantly induced by the interface on the two sides of CoFeB layer. The two-fold UMA strongly is stabilized in W/CoFeB/W trilayers up to 500°C. A maximum in-plane uniaxial anisotropy energy density (Ku) was observed for the 500°C annealed films, which is accompanied by the dominance of Hc┴ owing to the over-oxidation and/or occurrence of inter-diffusion across the interfaces. The oxidation and relieving of boron atoms in the CoFeB at higher annealing temperatures were confirmed by X-ray photoelectron spectroscopy (XPS). The control over the interface shared between the W and CoFeB is concluded to be essential in order to alter the strength of magnetic anisotropy. Hence, an investigation on W/CoFeB/W structures could be very beneficial for the modern Spin-Orbit Torque (SOT) based data storage applications and this inspires relevant research work to widen magnetic systems.

The impact of different annealing temperatures (Ta) and presence of capping layer on the structural, magnetic and transport properties of sputtered Co2FeAl (CFA (10 nm)) Heusler alloy thin films grown on Si (1 0 0) substrate is studied. The structural and topographical study reveal a direct impact of annealing on the crystallinity and surface roughness of the films. The Ferromagnetic resonance study shows that the Gilbert damping constant (α) is influenced by both crystallinity and roughness of the films and has a minimum value of 9.35(±0.15) × 10-3 for the 300 °C annealed (5.51(±0.27) × 10-3 for Al capped film) film having the lowest surface roughness. Also, the effect of capping layer on the spin dynamic properties of CFA layer is studied which reveals that a protective layer of low spin–orbit coupling material prevents the spin pumping to the formed oxide in case of uncapped CFA. The temperature-dependent resistivity depends on the roughness and crystallinity of the films (which are also a function of Ta) and revealed the dominance of weak localization at lower temperatures and electron–phonon scattering at higher temperatures. Temperature-dependent anomalous Hall effect measurements suggest the supremacy of the combined intrinsic and side jump contributions over skew scattering contribution.

We report controlled effect of Boron diffusion on annealing of Co60Fe20B20 (CoFeB) thin films grown on SiO2/Si(100) substrates using pulsed dc magnetron sputtering. X-ray diffraction studies indicated that the crystallization of CoFeB is achieved above 100°C via the formation of bcc CoFe with (110) preferred orientation. Saturation magnetization (µOMs) of the as-deposited film is found to be 1000 kA/m, which enhances upon annealing such that a value of µOMs of 1375 kA/m is observed in the sample annealed at 400°C while the coercivity decreases from 12 mT to 2 mT. A lowest value of 0.005±0.002 of the damping constant is evidenced for the sample annealed at 400°C. The tunability of the damping constant via the Boron out-diffusion from CFB achieved by controlling the annealing temperature is certainly important for spintronics device applications.

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 report a systematic investigation on structural and thermoelectric properties of Spark plasma sintered Lead telluride synthesized by hydrothermal route and a low temperature aqueous chemical route without using any organic solvent and surfactant. The as-synthesized powder samples obtained from these two different synthesis routes were identically subjected to spark plasma sintering. The size of nanocubes formed by the hydrothermal method, as evident from TEM-HRTEM images, is 50 nm; however, the samples synthesized by aqueous chemical route shows mixed morphology with particle size

In this work, a detail study on the effectiveness of high substrate temperature (TS) during deposition versus in situ annealing of the films at high temperature (TA) after sputtering at room-temperature is compared with an objective to obtain Heusler alloy thin films of Co2FeAl (CFA) having optimally low αint (with an upper bound of 1.75 × 10-3) and 12–17% smaller MS by employing ion beam sputtering technique and Si(100) as substrates for current induced magnetization switching application. In each of the two series of CFA films, prepared with different choice of TS and TA (lying in 300–773 K range) were explored for optimally tailoring their structural, static and dynamic magnetization properties. Structural study revealed that although all the CFA films were polycrystalline but the post-deposition annealed films were structurally optimal with higher density (6.36 ± 0.09 g/cm3) and lower interface roughness (0.48 ± 0.03 nm) compared to the CFA films grown at high TS (6.23 ± 0.06 g/cm3, 0.61 ± 0.01 nm). In plane field-angle dependent longitudinal magneto optical Kerr effect (L-MOKE) study revealed the existence of a coupling between the weak uniaxial and biaxial magnetic anisotropies present in these films, attributed to the employed deposition geometry. Ferromagnetic resonance (FMR) spectroscopy measurements, performed in both the geometries - in-plane as well as out of plane, revealed a lowest value of 1.19 (±0.08) × 10-3 of αint in the film post-annealed at 773 K. In addition, the observed non-linear relation between the αint and the dynamical ‘g’-factor suggests that the contribution of spin orbit interaction to the damping is far less compared to the damping contribution from the DOS present near the Fermi level. It is remarkable to note that the as-grown CFA films sputtered at room temperature exhibited a record lowest value of 1.73 (±0.09) × 10-3 of αint. Attainment of such small value of Gilbert damping and having moderate magnetization in high spin polarized Co2FeAl Heusler films sputtered on the Si (100) substrate opens up their great application potential in future spintronics devices.

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.

We report the structural and magneto-transport properties of co-sputtered MnAl alloy thin films grown on Si (1 0 0) at various substrate temperatures (Ts) ranging from room temperature to 500 °C. Analyses of the X-ray diffraction and DC-Magnetization data reveal that as the Ts of the films is changed, the volume fraction of ferromagnetic τ-MnxAl100-x (50

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 ...

The effect of adding Ta as a capping and buffer layer on ultrathin CFB(Co60Fe20B20) thin films has been investigated by magneto-optical Kerr effect. A large difference in the coercivity and saturation field is observed between the single layer CFB(2nm) and Ta(5nm)/CFB(2nm)/Ta(2nm) trilayer structure. In particular, the in-plane anisotropy energy is found to be 90kJ/m3 on CFB(2nm) and 2.22kJ/m3 for Ta(5nm)/CFB(2nm)/Ta(2nm) thin films. Anisotropy energy further reduced to 0.93kJ/m3 on increasing the CFB thinness in trilayer structure i.e., Ta(5nm)/CFB(4nm)/Ta(2nm). Using VSM measurement, the saturation magnetization is found to be 1230±50 kA/m. Low coercivity and anisotropy energy in capped and buffer layer thin films envisage the potential of employing CFB for low field switching applications of the spintronic devices.

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.