Browsing by Author "Vinod, Vellora Thekkae Padil"
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- ItemEffect of CoSi2 interfacial layer on the magnetic properties of Si vertical bar CoSi2 vertical bar Sm-Co thin films(ELSEVIER, RADARWEG 29, 1043 NX AMSTERDAM, NETHERLANDS, 2020-01-01) Saravanan, P.; Boominathasellarajan, S.; Sobel, Bartlomiej; Waclawek, Stanislaw; Vinod, Vellora Thekkae Padil; Černík, MiroslavMagnetic thin films with a layer sequence of Si vertical bar CoSi2 vertical bar Sm-Co were grown by direct sputter deposition at elevated temperatures, through interfacial diffusion between Si (1 0 0) substrate and the overlying Sm-Co layer. HR-TEM analysis revealed the occurrence of CoSi2 -interfacial layer close to the Si-substrate surface, with controllable thicknesses of similar to 20 and 35 nm at deposition temperatures: 450 and 500 degrees C, respectively. XRD studies confirmed the crystallization of Sm2Co17 and SmCo5 magnetic phases accompanied by the other phases such as CoSi2 and SmCoSi2 due to the intermixing of Co and Si-atoms at higher deposition temperatures. The measured coercivity values are found to be increased from 8.7 to 11.6 kOe at higher CoSi2-layer thickness. The angular-dependent hysteresis measurements demonstrated a distinct isotropic and uniaxial magnetic anisotropy characteristics for the Sm-Co films consisting of 35 and 20-nm thick CoSi2 interfacial layers, respectively and the associated magnetization reversal mechanisms are discussed using the Stoner-Wohlfarth model. The temperature coefficients of remanence (alpha) and coercivity (beta) were determined from the temperature-dependent hysteresis curves. The Sm-Co films consisting of 35-nm thick CoSi2-layer exhibited a better thermal stability with 'alpha' and 'beta' values of 0.35 +/- 0.05%/degrees C and -0.13 +/- 0.02%/degrees C, respectively. The results of present study provide splendid opportunities for exploiting the potential of CoSi2 as an under layer, for growing the Sm-Co films towards high-temperature applications.
- ItemInterfacial layer formation during high-temperature deposition of Sm-Co magnetic thin films on Si (100) substrates(ELSEVIER SCI LTD, THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, OXON, ENGLAND, 2019-03) Saravanan, P.; Boominathasellarajan, S.; Sobel, Bartlomiej; Waclawek, Stanislaw; Vinod, Vellora Thekkae Padil; Talapatra, A.; Mohanty, J.; Černík, MiroslavThe interfacial layer that has formed during the deposition of similar to 240-nm thick Sm-Co films on the bare Si (100) substrate was investigated at different deposition temperatures, T-d,T-Sm-Co: 400, 450 and 500 degrees C with respect to structural and magnetic properties of Sm-Co films. X-ray diffraction analysis showed the crystallization of both Sm2Co17(R) and SmCo5(H) magnetic phases. Rutherford back scattering studies demonstrated that the surface-diffusion reactions between the Sm-Co layer and Si-surface not only accompanied by the quasi-layered growth of CoSi2-phase; but also led to the formation of SmCoSi2-phase. Cross-sectional transmission electron microscopy analysis revealed uneven boundary with deeply grown CoSi2-layer and Moire fringes at limited regions of Co/Si interface. Magnetic measurements showed a square hysteresis loop with maximum values of coercivity (11.6 kOe) and remanence ratio (0.99) for the films grown at 500 degrees C. Magnetic force microscopy images depicted patch-like domains with increasing phase contrast against T-d,T-Sm-Co. In addition, the changes that has occurred in the magnetization reversal processes accompanied by coercivity enhancement due to higher T-d,T-Sm-Co is discussed in the context of domain morphology and first-order reversal curves.
- ItemStructural and magnetic properties of rare-earth-free MnAl(MCNT)/Fe nanocomposite magnets processed by resin-bonding technique(SPRINGER, VAN GODEWIJCKSTRAAT 30, 3311 GZ DORDRECHT, NETHERLANDS, 2020-05) Saravanan, P.; Saju, Sarah; Vinod, Vellora Thekkae Padil; Černík, MiroslavIn this study, the potential of multi-walled carbon nanotubes (MCNT) in processing rare-earth-free MnAl(MCNT)/Fe nanocomposite magnets was exploited through adopting a combination of surfactant-assisted milling and resin-bonding techniques. The required hard and soft magnetic phases such as MnAl(MCNT) and alpha-Fe, respectively, were individually subjected to surfactant-assisted high-energy ball milling. The surfactant-coated MnAl(MCNT) and Fe nanopowders, thus, obtained were characterized with respect to their structural and magnetic properties. Relatively, a very high coercivity, H-c (4.48 kOe), was obtained for the surfactant-coated MnAl(MCNT) powders after 6 h of milling, while in the case of Fe powders with high saturation magnetization, M-s (218.6 emu/g) was achieved at 3 h of surfactant-assisted milling. The MnAl(MCNT) powders with high H-c were mixed with the Fe powders of high M-s with different weight percentages: 0, 5 and 10. The nanocomposite powder mixtures were further milled for 1 h and then processed in the form of resin bonded magnets under aligning magnetic field of 20 kOe. The obtained bonded nanocomposite magnet, i.e. MnAl(MCNT) with 5 wt% of Fe addition demonstrated a good combination of high M-s (63.7 emu/g) and high H-c (4.46 kOe).
- ItemStudy on the field-cooling induced magnetic interactions in Gd-doped NiO nanoparticles(ELSEVIER, RADARWEG 29, 1043 NX AMSTERDAM, NETHERLANDS, 2020-01-01) Gokul, B.; Saravanan, P.; Matheswaran, P.; Pandian, M.; Sathyamoorthy, R.; Asokan, K.; Vinod, Vellora Thekkae Padil; Černík, MiroslavWe herein investigate the novel magnetic interactions, such as exchange bias (EB), memory effect (ME) and magnetic relaxation dynamics (MRD) in NiO and 10 wt% Gd doped NiO nanoparticles synthesized by hydrothermal process. X-ray diffraction studies showed crystallization of face-centered-cubic structure for both NiO and Gd-doped NiO nanoparticles. Transmission electron microscopy analysis revealed a spherical morphology for both samples and their mean particle sizes were estimated as 24.5 and 10.3 nm for the pure and Gd-doped NiO nanoparticles, respectively. SQUID magnetic measurements demonstrated the occurrence of large EB coupling: 1.04 and 0.767 kOe; and enhanced coercive fields: 1.75 and 1.27 kOe, for the pure and Gd-doped NiO nanoparticles, respectively. The size-dependent magnetic properties such as, EB, ME and MRD is found to vanish at the average blocking temperature and interestingly, these properties set-in on cooling the samples at 5 K under applied field of 5 kOe. The surface defects such as oxygen vacancies and the Gd2O3 impurity phase played a significant role in determining the EB and ME characteristics of NiO nanoparticles.