@iuac.res.in
Scientist H
Inter University Accelerator Centre
ion beam interactions, Synchrotron-based XAS and other techniques
Scopus Publications
Akram Krichene, Wahiba Boujelben, Kunal N. Rathod, Keval Gadani, Chi–Liang Chen, Asokan Kandasami, Nikesh A. Shah, and Piyush S. Solanki
Elsevier BV
R.B. Sonpir, D.V. Dake, N.D. Raskar, V.A. Mane, K. Asokan, and B.N. Dole
Elsevier BV
N.D. Raskar, D.V. Dake, V.A. Mane, R.B. Sonpir, M. Vasundhara, K. Asokan, U. Deshpande, R. Venkatesh, V.D. Mote, and B.N. Dole
Elsevier BV
Kapil Dev, V R Reddy, Rohit Medwal, Surbhi Gupta, C L Dong, C L Chen, K Asokan, and S Annapoorni
IOP Publishing
Abstract The domain reversal and magnetization dynamics of electrodeposited permalloy (Fe20Ni80) thin films on conducting ITO/glass substrate was investigated using Magneto-optic Kerr effect microscopy and ferromagnetic resonance. Permalloy thin films were electrodeposited with thickness ranging from 66 nm to 330 nm. Synchrotron XRD confirmed the deposited permalloy in FCC phase without any impurity. The squared hysteresis with very low coercivity (Hc ∼ 5 Oe) established soft magnetic nature of the films. Further, angular MOKE hysteresis measurements with simultaneous domain imaging revealed four-fold surface anisotropy in as-deposited film ensuing magnetization reversal via branched and ripple domains. The annealing treatment in Ar+H2 atmosphere removed surface anisotropy and renovated the magnetization reversal through 180° branched domains with rapid magnetization switching. Ferromagnetic resonance spectroscopy discloses reduction in the gyromagnetic ratio (γ) as well as in Gilbert damping parameter (α) as the film thickness increases. The lowest Gilbert damping for 330 nm film measured at 0.022, which further reduced to 0.018 after annealing. The combination of rapid magnetization switching and low Gilbert damping in the electrodeposited permalloy thin films render them promising for implementation in high-frequency microwave devices devices and magnetic sensors.
Hetal Kundalia, Brinda Vyas, Malay Udeshi, Ashish Ravalia, K Asokan, and D.G. Kuberkar
Elsevier BV
P. Jeya, L. Kungumadevi, R. Yuvakkumar, G. Ravi, Kandasami Asokan, T.S. Senthil, Saju Subin, and Sagadevan Suresh
Elsevier BV
Naveenkumar K.R, P. Kannappan, Abhishek Kumar Mishra, Thanigai Arul Kumaravelu, C.L. Dong, R.C. Meena, and Asokan Kandasami
Elsevier BV
Debashish Sen, Shaila Bahl, Pooja Seth, Birendra Singh, A. Pandey, Mohammad Zulfequar, and Asokan Kandasami
Elsevier BV
Jeya P, L. Kungumadevi, Sebin K. Binu, Anandhu Jayakumar, and Asokan Kandasami
Elsevier BV
Suniksha Gupta, Smita Howlader, K. Asokan, M. K. Banerjee, and K. Sachdev
Springer Science and Business Media LLC
Kurinjinathan Panneerselvam, Anita R. warrier, Roselin Ranjitha Mathiarasu, Ta Thi Thuy Nga, Ramana Ramya J, Thanigai Arul Kumaravelu, Wu-Ching Chou, Yu-Cheng Huang, Jeng-Lung Chen, Chi-Liang Chen,et al.
Elsevier BV
Keval Gadani, Faizal Mirza, Davit Dhruv, K. Asokan, P. S. Solanki, N. A. Shah, and A. D. Joshi
Springer Science and Business Media LLC
N.D. Raskar, D.V. Dake, V.A. Mane, R.B. Sonpir, H.A. Khawal, V.D. Mote, M. Vasundhara, K. Asokan, K.P. Gattu, and B.N. Dole
Elsevier BV
I-Han Wu, Arvind Chandrasekar, Kumaravelu Thanigai Arul, Yu-Cheng Huang, Ta Thi Thuy Nga, Chi-Liang Chen, Jeng-Lung Chen, Da-Hua Wei, Kandasami Asokan, Ping-Hung Yeh,et al.
Elsevier BV
Bhargav Rajyaguru, Keval Gadani, Himanshu Dadhich, Davit Dhruv, V. Ganesan, K. Asokan, N.A. Shah, and P.S. Solanki
Elsevier BV
Hardik Gohil, Keval Gadani, Hetal Boricha, Bhargav Rajyaguru, Himanshu Dadhich, Nisarg Raval, Davit Dhruv, V.R. Rathod, N.P. Barde, P.P. Bardapurkar,et al.
Elsevier BV
A. Kumar, M. Baral, A. Kandasami, S. K. Mandal, R. Urkude, S. Bhunia, and V. R. Singh
AIP Publishing
The present study focuses on the oxygen (O)-ion implantation-induced structural and electronic modifications in the single crystals of strontium-titanate (s-STO) using synchrotron-based x-ray diffraction (XRD), x-ray photoemission spectroscopy (XPS), and resonant x-ray photoemission spectroscopy. The crystallinity of the epitaxially aligned phases of s-STO is confirmed through XRD. This direct evidence of heavy ion implantation is supported by the Monte Carlo-based simulation of stopping and range of ions in matter/transport of ions in matter. XPS at different core levels is performed to detect the exact oxidation state of Ti ions in s-STO. The dominance of Ti3+ over Ti4+ upon oxygen implantation suggests the disorder in the perovskite material, primarily in the form of oxygen vacancies (VO). The confirmation of VO is explicitly shown by the enhancement in the spectral area of the assigned peak in the O 1s XPS. Resonant photoemission spectroscopy measurements were performed by varying photon energy from 32 to 46 eV to understand the nature of the valence band electronic structure of s-STO. The resonance in the different hybridized states of s-STO is confirmed by the spectral features of constant initial state plots. There is a correlation between the defective state of Ti and the oxygen-deficient state. The transformation from SrTiO3 to SrTiO2.5, partially or completely, is essentially required to underline any modification in the electronic properties of s-STO. s-STO is in a mixed state of an ionic conductor and an electronic conductor. This study outlines the creation of VO due to O-ion implantation and investigates the changes in the electronic structures of s-STO.
Kishor H. Gavhane, M.S. Bhadane, Preeti P. Kulkarni, Vikas Kashid, V.S. Ghemud, K. Hareesh, K. Asokan, Anjali Kshirsagar, V.N. Bhoraskar, S.D. Dhole,et al.
Elsevier BV
Riya Dawn, Rajashri Urkude, Shilpa Tripathi, Satyaban Bhunia, Weng Weei Tjiu, Zainul Aabdin, Asokan Kandasami, and Vijay Raj Singh
IOP Publishing
Abstract The evolution of the nanostructures and electronic properties of 5% cobalt-doped TiO2 nanoparticles (NPs) annealed at 400 °C, 600 °C, and 800 °C have been investigated to understand the structural phase transformations through chemical co-precipitation synthesis. A detailed analysis of the X-ray Diffractogram confirms that the sample annealed at 400 °C is anatase, at 600 °C, the mixed phase of anatase and rutile evolves, and at 800 °C, the sample is of rutile structure. A detailed morphological study by scanning transmission electron microscope provides the particle size, lattice spacing, and variation in polycrystalline grain growth at different phases. Electron Energy Loss Spectroscopy analysis indicates from the O K, Co, and Ti L 2,3-edges that Ti4+ ions are primarily in an octahedral symmetry with the oxygen ligands changing their structural phases from anatase to mixed phase and then stable rutile phase with increasing temperature of annealing. X-ray Absorption Near Edge Spectroscopy (XANES) extracts information about the varying oxidation states and 3-dimensional geometry of Ti-ions. The unresolved issues of the structural details at the atomic-scale picture with the local environment of the cation with a few nearest neighbour shells are derived from Extended X-ray Absorption Fine Structure (EXAFS) and pre-edge parts of the absorption spectra. The limits of EXAFS in this situation of asymmetric bond length disorder, which is typical for mixed-valence oxides, are generated to reconcile the two data and highlight the value of pre-edge XANES analysis for identifying local heterogeneities in structural and compositional motifs. TiO2 possesses unique properties depending upon its structural phase. The Ti L 2,3-edge spectrum indicates that there is an octahedron connectivity of the Oxygen atoms at the anatase state which transforms to a higher energetic tetrahedral correspondence as it proceeds towards the rutile phase. The driving force behind such interest is to modulate the properties of TiO2 NPs to better photocatalytic material and to integrate its application as a versatile energy storage device.
Arkaprava Das, Camille Latouche, Stephane Jobic, Eric Gautron, Amina Merabet, Marcin Zajac, Akinori Shibui, Peter Krüger, Wei-Hsiang Huang, Chi-Liang Chen,et al.
Elsevier BV
Ashutosh Kumar, Akhilananda Kumar, Asokan Kandasami, and Vijay Raj Singh
Springer Science and Business Media LLC
R.B. Sonpir, D.V. Dake, N.D. Raskar, V.A. Mane, K. Asokan, U. Deshpande, M. Vasundhara, and B.N. Dole
Elsevier BV
Karthikeyan Kandhasamy, Matheswaran Palanisamy, Shankar Hari, Shradha Suman, Kamatchi Jothiramalingam Sankaran, Pandiyarasan Veluswamy, Gokul Bangaru, and Asokan Kandhasami
Elsevier BV
A. Kumar, T. Ghosh, Z. Aabdin, J. Roy, V. K. Verma, A. Ghosh, S. K. Sahoo, R. Urkude, S. Bhunia, U. K. Goutam,et al.
AIP Publishing
Spintronics-based studies have produced significant attention in the last decade while claiming the observation of room temperature ferromagnetism (RTFM). Nevertheless, there is a lack of consensus on a mechanism responsible for this phenomenon. In this study, we focus on Cu-doped ZnO (ZCO) to understand the microscopic origin of RTFM and the role of different oxidation states of Cu in RTFM. We have performed different spectroscopic techniques using synchrotron facilities. The values of spin-moment obtained from x-ray magnetic circular dichroism sum-rule truly exhibit a ferromagnetic interaction in the nanocrystalline powder of ZCO with ∼0.58 μB for 5% of Cu concentration in the total fluorescence yield mode. Such an enhanced magnetization is attributed to the presence of Cu2+, which is mainly localized in the bulk region. Cu in ZCO is mostly dominated by the presence of Cu2+. This is clearly reflected by the profiles of x-ray photoemission spectroscopy. Consequently, the weakly magnetized total electron yield mode is attributed to a state of magnetic frustration as the majority of Cu3+ is found on the surface. Some of these Cu3+ when come in the vicinity of Cu2+ ions result in a highly correlated state of double exchange mechanism, which is the microscopic origin of RTFM in ZCO. The coupling between Cu2+-Cu3+ is mediated via oxygen vacancies (VO), the presence of which is confirmed through the features of electron energy loss spectroscopy over different edges. The confirmation of VO is also supported by the deconvolution of E2high-phonon in the Raman spectra. Moreover, the defects in the local electronic structures of ZCO are demonstrated by the deconvoluted spectra of Cu L3 x-ray absorption spectroscopy. The images obtained from high-resolution transmission electron microscopy confirm the incorporation of Cu into the wurtzite crystal of ZnO. A clear enhancement in magnetization upon an increase in carriers of Cu in ZCO indicates carrier-induced ferromagnetism. Cu2+ and VO are the two attributes of RTFM in ZCO.
Akanksha Motla, Thanigai Arul Kumaravelu, Chung-Li Dong, Chi-Liang Chen, K. Asokan, and S. Annapoorni
Springer Science and Business Media LLC