| 1. |
- Akansel, Serkan, 1983-, et al.
(author)
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Thickness dependent enhancement of damping in Co2FeAl/β-Ta thin films
- 2018
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In: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 97:13
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Journal article (peer-reviewed)abstract
- 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 thickness (tCFA ); 8, 10, 12, 14, 16, 18 and 20 nm were prepared and all samples were capped with a 5 nm thick b-Ta layer. The thickness dependent static and dynamic properties of the films were studied by SQUID magnetometry, in-plane as well as out-of-plane broadband VNA-FMR measurements and angle dependent cavity FMR measurements. The saturation magnetization and the coercive field were found to be weakly thickness dependent and lie in the range 900 – 950 kA/m and 0.53 – 0.87 kA/m, respectively. The effective damping parameter ( αeff) extracted from in-plane and out-of-plane FMR results reveal a 1/tCFA dependence, the values for the in-plane αeff being larger due to two-magnon scattering (TMS). The origin of the αeff thickness dependence is spin pumping into the non-magnetic b-Ta layer and in case of the in-plane αeff also a thickness dependent TMS contribution. From the out-of-plane FMR results, it was possible to disentangle the different contributions to αeff and to the extract values for the intrinsic Gilbert damping (αG ) and the effective spin-mixing conductance (g_eff^↑↓ ) of the CFA/ b-Ta interface, yielding αG=1.1X10-3 and g_eff^↑↓=2.90x1019 m-2.
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| 2. |
- Barwal, Vineet, et al.
(author)
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Anisotropic Gilbert Damping in B2 ordered Full Heusler Alloy Co2MnAl thin films
- 2020
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In: DAE Solid State Physics Symposium 2019. - : AIP Publishing. - 9780735420250
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Conference paper (peer-reviewed)abstract
- 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.
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| 3. |
- Barwal, Vineet, et al.
(author)
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Growth and Dynamic Magnetization Study of Co2MnAl Full Heusler Alloy Thin Films
- 2018
-
In: 2nd International Conference on Condensed Matter and Applied Physics (ICC-2017). - : American Institute of Physics (AIP). - 9780735416482
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Conference paper (peer-reviewed)abstract
- Structural and dynamic magnetization properties of Co2MnAl (CMA) full Heusler alloy thin films grown on Si (100) substrates at different substrate temperatures (T-s) room temperature (RT), 200 degrees C, 300 degrees C, 400 degrees C and 500 degrees 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 (H-r) and line width (Delta H), the effective saturation magnetization (4 pi M-eff) and damping constant () have been evaluated. The lowest damping constant was found to be 0.007 +/- 0.002 for the film grown at T-s=200 degrees C which is comparable to the reported value.
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| 4. |
- Barwal, Vineet, et al.
(author)
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Growth dependent magnetization reversal in Co2MnAl full Heusler alloy thin films
- 2018
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In: Journal of Applied Physics. - : AMER INST PHYSICS. - 0021-8979 .- 1089-7550. ; 123:5
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Journal article (peer-reviewed)abstract
- Angular dependent magnetization reversal has been investigated in Co2MnAl (CMA) full Heusler alloy thin films grown on Si(100) at different growth temperatures (T-s) by DC-magnetron sputtering. An M-shaped curve is observed in the in-plane angular (0 degrees-360 degrees) 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. Further, the analysis of angular dependent squareness ratio (M-r/M-s) indicates that our films clearly exhibited twofold uniaxial anisotropy, which is related to self-steering effect arising due to the obliquely incident flux during the film-growth.
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| 5. |
- Barwal, Vineet, et al.
(author)
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Spin gapless semiconducting behavior in inverse Heusler Mn2-xCo1 +/- xAl (0 x 1.75) thin films
- 2021
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In: Journal of Magnetism and Magnetic Materials. - : Elsevier. - 0304-8853 .- 1873-4766. ; 518
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Journal article (peer-reviewed)abstract
- 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.
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| 6. |
- Barwal, Vineet, et al.
(author)
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Structural and magneto-transport properties of co-sputtered MnAl thin films
- 2020
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In: Journal of Magnetism and Magnetic Materials. - : ELSEVIER. - 0304-8853 .- 1873-4766. ; 503
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Journal article (peer-reviewed)abstract
- 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 (T-s) ranging from room temperature to 500 degrees C. Analyses of the X-ray diffraction and DC-Magnetization data reveal that as the T-s of the films is changed, the volume fraction of ferromagnetic tau-MnxAl100-x (50 < x < 60) metastable phase retained in the films changes from 3.7 to 9.5% and the remaining fraction comprises of non-magnetic beta-MnAl and gamma(2)-phases. The temperature-dependent longitudinal resistivity variation demonstrates a semi-metallic nature in all these films. The temperature dependence of Hall Effect data further corroborates this semi-metallic behavior. The magnetoresistance (MR) response of these films is measured in the range of 10-300 K, both in the in-plane as well as out-of-plane magnetic field configurations. The out-of-plane MR is significantly larger than in-plane MR due to electron-hole compensation (which stems from mull-band effects) which is discussed further by plotting the Kohler's plot for the thin films.
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| 7. |
- Dutta, Soma, et al.
(author)
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Manipulating ultrafast magnetization dynamics of ferromagnets using the odd-even layer dependence of two-dimensional transition metal di-chalcogenides
- 2024
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In: Nanoscale. - : Royal Society of Chemistry. - 2040-3364 .- 2040-3372. ; 16:8, s. 4105-4113
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Journal article (peer-reviewed)abstract
- Two-dimensional transition metal dichalcogenides (TMDs) have drawn immense interest due to their strong spin-orbit coupling and unique layer number dependence in response to spin-valley coupling. This leads to the possibility of controlling the spin degree of freedom of the ferromagnet (FM) in thin film heterostructures and may prove to be of interest for next-generation spin-based devices. Here, we experimentally demonstrate the odd-even layer dependence of WS2 nanolayers by measurements of the ultrafast magnetization dynamics in WS2/Co3FeB thin film heterostructures by using time-resolved Kerr magnetometry. The fluence (photon energy per unit area) dependent magnetic damping (alpha) reveals the existence of broken symmetry and the dominance of inter- and intraband scattering for odd and even layers of WS2, respectively. The higher demagnetization time, tau m, in 3 and 5 layers of WS2 is indicative of the interaction between spin-orbit and spin-valley coupling due to the broken symmetry. The lower tau m in even layers as compared to the bare FM layer suggests the presence of a spin transport. By correlating tau m and alpha, we pinpointed the dominant mechanisms of ultrafast demagnetization. The mechanism changes from spin transport to spin-flip scattering for even layers of WS2 with increasing fluence. A fundamental understanding of the two-dimensional material and its odd-even layer dependence at ultrashort timescales provides valuable information for designing next-generation spin-based devices. Odd-even WS2 layer number dependent ultrafast demagnetization and damping are studied by varying the pump fluence.
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| 8. |
- Gupta, Nanhe Kumar, et al.
(author)
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Effect of post-annealing on the magnetic properties of sputtered Mn56Al44 thin films
- 2018
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In: 2nd International Conference On Condensed Matter And Applied Physics (ICC-2017). - : American Institute of Physics (AIP). - 9780735416482
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Conference paper (peer-reviewed)abstract
- Ma(56)Al(44) (MnAl) thin films of constant thickness (similar to 30nm) were grown on naturally oxidized Si substrates using DC-magnetron sputtering. Effect of deposition parameters such as sputtering power, substrate temperature (T-s), and post-annealing temperature have been systematically invstigated. X-ray diffraction patterns revealed the presence of mixed phases, namely the tau- and beta-MnAl. The highest saturation magnetization (M.$) was found to be 65emu/cc using PPMSVSM in film grown at T-s =500 degrees C. The magnetic ordering was found to get significantly improved by performing post annealing of these as-grwon at 400 degrees C for 1 hr in the presence of out-of-plane magnetic field of similar to 15000e in vacuum. In particular, at room temperature (RT), the Ms got enhanced after magnetic annealing from 65mm/cc to 500 emu/cc in MnAl films grown at T-s=500 degrees C. This sample exhibited a magneto-resistance of similar to 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 MnAI, a metastable ferromagnetic system which possesses the highest perpendicular magnetic anisotropy at RT till date.
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| 9. |
- Gupta, Nanhe Kumar, et al.
(author)
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Influence of Annealing on Boron Diffusion from Obliquely Sputtered Co60Fe20B20 Thin Films
- 2020
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In: DAE Solid State Physics Symposium 2019. - : AIP Publishing. - 9780735420250
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Conference paper (peer-reviewed)abstract
- 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.
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| 10. |
- Gupta, Rahul, et al.
(author)
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Co2FeAl Full Heusler Compound Based Spintronic Terahertz Emitter
- 2021
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In: Advanced Optical Materials. - : John Wiley & Sons. - 2162-7568 .- 2195-1071. ; 9:10
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Journal article (peer-reviewed)abstract
- 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.
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