DEVARAJAN U
@unom.ac.in
Dr. D.S. Kothari Post Doctoral Fellow, Department of Nuclear Physics,
University of Madras, Chennai
EDUCATION
Research Experience:
Currently, I am working as Dr. D.S. Kothari Post Doctoral Fellow at Department of Nuclear Physics, University of Madras, Chennai (28th December 2018 - Present).
I completed SERB National Post-Doctoral Fellowship at Department of Physics, Indian Institute of Science Education and Research, Pune (29th August 2016- 28th August 2018).
Academic details:
1. Ph.D in Physics at Bharathidasan University, Tiruchirappalli, Tamil Nadu, India on August 2016.
2. M.Phil in Nuclear Physics, University of Madras, Tamil Nadu, India, Chennai, August - 2009.
3. M.Sc in Materials Science, Anna University, Chennai,Tamil Nadu, India, April – 2008.
4. B.Sc in Physics, Thiruvalluvar University, Vellore, Tamil Nadu, India, April - 2006.
RESEARCH INTERESTS
Materials science, High pressure and low temperature physics, Solid state Physics and magnetism, Superconductivity, Crystal Growth, thin films and Multi ferroics.
Scopus Publications
Scholar Citations
Scholar h-index
Scholar i10-index
Scopus Publications
U. Devarajan, P. Sivaprakash, Alga B. Garg, Ikhyun Kim, and S. Arumugam
Springer Science and Business Media LLC
U. Devarajan, Sunil Nair, and C. Venkateswaran
Elsevier BV
U. Devarajan, P. Sivaprakash, C. Venkateswaran, P. Hariharan, Y. Kawamura, C. Sekine, and S. Arumugam
Elsevier BV
D. Paul Joseph, U. Devarajan, Jean Maria Fernandes, R. Ramarajan, M. Kovendhan, Nandarapu Purushothamreddy, Reddivari Muniramaiah, and C. Venkateswaran
Elsevier BV
U Devarajan and Sunil Nair
IOP Publishing
S. Arumugam, U. Devarajan, S. Esakki Muthu, Sanjay Singh, R. Thiyagarajan, M. Manivel Raja, N.V. Rama Rao, and Alok Banerjee
Elsevier BV
Abstract In this work, we have investigated structural, transport, magnetic, magnetocaloric (MC) properties and critical exponents analysis of the (Ni 2.1− x Co x )Mn 0.9 Ga ( x = 0, 0.04, 0.12 and 0.2) Heusler alloys. For all compositions, cubic austenite (A) phase with metallic character is observed at room temperature (RT). With increasing of Co content, magnitude of resistivity decreases, whereas residual resistivity ( ρ 0 ) and electron scattering factor ( A ) increases linearly. Magnetic measurements exhibit that ferromagnetic (FM) Curie temperature ( T C A ) increases towards RT by increasing Co concentration. All samples show conventional MC and maximum magnetic entropy change (Δ S M peak ) of −2.8 Jkg −1 K −1 is observed for x = 0.12 at 147 K under 5 T. Further, hysteresis is observed between cooling and warming cycles around FM-PM ( T C A ) transition in x = 0, 0.04 samples, which suggests that first order nature of transition. However, there is no hysteresis across T C A for x = 0.12 and 0.2 samples suggesting second-order nature of the transition. The critical exponents are calculated for x = 0.12 sample around T C A using Arrott plot and Kouvel-Fisher method, the estimated critical exponents are found closer to the mean-field model reveals the long range ferromagnetic ordering in this composition.
S. Arumugam, Subrata Ghosh, Arup Ghosh, U. Devarajan, M. Kannan, L. Govindaraj, and Kalyan Mandal
Elsevier BV
Abstract In this study, we report the effect of hydrostatic pressure (P) and magnetic field (H) on the magnetization, magnetocaloric effect and exchange bias in a Ni45.5Co2Mn37.5Sn15 Heusler alloy. At ambient pressure, the martensitic transition temperature (TM) shifts to lower temperatures with a rate of dTM/dμ0H ∼ 3.29 K/T. On the other hand, TM increases rapidly to higher temperatures with dTM/dP ∼31.90 K/GPa when hydrostatic pressure is applied. The peak value of magnetic entropy change due to change in magnetic field of 5 T is found to decrease with increasing pressure. Although, the relative cooling power (RCP) increases from ∼189 Jkg-1 to ∼ 204 Jkg-1 during cooling cycle, a significant drop in net RCP is obtained from the measurements under heating cycle. The coercivity of the sample at a given temperature merely changes, but the exchange bias effect is improved by applying pressure.
U Devarajan, M Kannan, R Thiyagarajan, M Manivel Raja, N V Rama Rao, Sanjay Singh, D Venkateshwarlu, V Ganesan, M Ohashi, and S Arumugam
IOP Publishing
U. Devarajan, Sanjay Singh, S. Esakki Muthu, G. Kalai Selvan, P. Sivaprakash, S. Roy Barman, and S. Arumugam
AIP Publishing
The resisitivity of Ni2−XMn1+XGa (X = 0 and 0.15) magnetic shape memory alloys has been investigated as a function of temperature (4–300 K) and hydrostatic pressure up to 30 kilobars. The resistivity is suppressed (X = 0) and enhanced (X = 0.15) with increasing pressure. A change in piezoresistivity with respect to pressure and temperature is observed. The negative and positive piezoresistivity increases with pressure for both the alloys. The residual resistivity and electron-electron scattering factor as a function of pressure reveal that for Ni2MnGa the electron-electron scattering is predominant, while the X = 0.15 specimen is dominated by the electron-magnon scattering. The value of electron-electron scattering factor is positive for both the samples, and it is decreasing (negative trend) for Ni2MnGa and increasing (positive trend) for X = 0.15 with pressure. The martensite transition temperature is found to be increased with the application of external pressure for both samples.
S. Esakki Muthu, N. V. Rama Rao, R. Thiyagarajan, U. Devarajan, M. Manivel Raja, and S. Arumugam
AIP Publishing
In this work, we report the influence of chemical substitution of Ni site by Cu, magnetic field of 50 kOe, and external pressure effect on martensite and intermartensite transformations in Ni49-xCuxMn38Sn13 (0.5 ≤ x ≤ 2) Heusler alloys. The substitution of Cu for Ni decreases the lattice parameter and introduces the intermartensitic transformation in this alloy series. Further, the intermartensitic transformation vanishes for higher Cu content (x = 2). The application of external magnetic field and hydrostatic pressure suppresses the intermartensitic transformation in Ni49-xCuxMn38Sn13 (0.5 ≤ x ≤ 1.5) and Ni49-xCuxMn38Sn13 (x = 0.5) alloys, respectively. Also, the external magnetic field favors the stabilization of austenite phase while the external hydrostatic pressure favors the martensite phase.
U. Devarajan, S. Esakki Muthu, S. Arumugam, Sanjay Singh, and S. R. Barman
AIP Publishing
The effect of hydrostatic pressure on the magnetic and magnetocaloric properties of Ni2−XMn1+XGa (X = 0, 0.15) Heusler alloys around the martensitic transformation temperature (TM) has been investigated. We find that magnetic field increases and decreases the characteristic transitions temperature for X = 0 and 0.15, respectively, and increases the saturation magnetization of martensite phase for both the alloys. However, the hysteresis width decreases for both the alloys as we increase the magnetic field to 5 T. Application of hydrostatic pressure increases (decreases) the TM for X = 0 and 0.15. Pressure stabilizes the martensite phase with the increase of TM for Ni2MnGa, whereas the austenite phase gets stabilized with the decrease of TM in Ni1.85Mn1.15Ga (x = 0.15). Metamagnetic-like transition is suppressed for both the specimens with increasing pressure. The maximum magnetic entropy change (ΔSM max) is found to reduce from 19.2 J kg−1 K−1 (P = 0) to 6.04 J kg−1 K−1 (P = 9.69 kilobars) around TM for N...
B. Munirathinam, M. Krishnaiah, U. Devarajan, S. Esakki Muthu, and S. Arumugam
Elsevier BV
Abstract Half doped mixed valence manganite system La 0.5 Ca 0.45− x Sr x Ba 0.05 MnO 3 (with x =0.1, 0.2, and 0.3) synthesized through a low temperature nitrate route is systematically investigated in this paper. The electronic transport and magnetic properties are analyzed and compared apart from the study of unit cell structure and composition. The system is found to crystallize only in orthorhombic structure (Pnma) and the electronic phase transitions are observed to be of second order. The charge and orbital ordering have been observed to coexist with ferromagnetism in x =0.1 compound. Application of small polaron and variable range hopping models to resistivity data of the system corresponding to high temperature range shows increasing mobility of e g electrons with x , with the later model describing the electronic transport very closely than the former. The temperature dependent magnetization of the compounds shows monotonic increase of paramagnetic to ferromagnetic transition ( T C ) with x . Ferromagnetism is exhibited for the complete temperature range down from respective T C in contrast to antiferromagnetism usually exhibited by half-doped compounds in the low temperature range. The plots of magnetization versus magnetic field reveal a transition from soft to hard magnetic character for all the compounds as the temperature is lowered.
R. Thiyagarajan, Guochu Deng, S. Arumugam, D. Mohan Radheep, U. Devarajan, A. Murugeswari, P. Mandal, Ekaterina Pomjakushina, and Kazimierz Conder
AIP Publishing
The magnetic properties of half-doped Pr(Sr1−xCax)2Mn2O7 (x = 0.4 and 0.9) single crystals have been investigated under magnetic field (H) and hydrostatic pressure (P). Analysis of magnetization data reveals that, for x = 0.4 sample, only one charge-orbital ordering (CO-OO) transition occurs which decreases very slowly with P, while the antiferromagnetic ordering transition shifts towards higher temperature with the increase of P. For x = 0.9 sample, with the increase of P, the low-temperature CO-OO transition temperature decreases and the high-temperature CO-OO transition remains unaffected while antiferromagnetic and structural transition temperatures increase.
S. Esakki Muthu, N. V. Rama Rao, D. V. Sridhara Rao, M. Manivel Raja, U. Devarajan, and S. Arumugam
AIP Publishing
We report the effect of Ni/Mn variation on the exchange bias properties in the bulk Mn-rich Ni50−xMn37+xSn13 (0 ≤ x ≤ 4) Heusler alloys. The excess Mn content was found to increase the exchange bias field while it decreases the exchange bias blocking temperature (TEB) from 149 to 9 K. A maximum shift in the hysteresis loop of 377 Oe is observed for the Ni46Mn41Sn13 alloy. As compared to Mn/Sn variation, Ni/Mn variation strongly influences the exchange bias properties in Ni-Mn-Sn alloys. We observed that if the Mn content is above 37 at. % in Ni-Mn-Sn alloys, the TEB value would show a decreasing trend either by varying the Ni or Sn content.
RECENT SCHOLAR PUBLICATIONS
MOST CITED SCHOLAR PUBLICATIONS
Publications
List of papers Published / Accepted in National / International Journals:
1. D. Paul Joseph, U. Devarajan, et al , J. Surfaces and interfaces, 23 100918 (2021). [I.F: 3.724].
2. U. Devarajan et al, Materials Research Express, 6, 106117 (2019). [I.F: 1.410].
3. S. Arumugam, U. Devarajan et al, J. Mag. Mag. Mater. 442 460-467 (2017). [I.F: 3.046].
4. S. Arumugam, , U. Devarajan et al., J. All. Comp. 712 714-719 (2017). [I.F: 4.65].
5. U. Devarajan, et al. J. Phys. D: Appl. Phys. 49 065001 (2016). 3.169]
6. U. Devarajan, et al, Appl. Phys. Lett. 105, 252401 (2014). [I.F: 3.597]
7. S. Esakki Muthu, U. Devarajan et al, Appl. Phys. Lett. 104, 092404 (2014). [I.F: 3.597]
8. U. Devarajan, et al, J. Appl. Phys. 114, 053906 (2013). [I.F: 2.286]
9. S. Esakki Muthu, U. Devarajan et al, Indian journal of Cryogenics. 37, 1-4 (2012). [I.F: 0.0]
10. B. Munirathinam, M. Krishnaiah, U. Devarajan et al, Journal of Physics and Chemistry of Solids 73, 925-930 (2012). [I.F: 2.870]
11. S. Esakki Muthu, U. Devarajan, et al, J. Appl. Phys. 110, 023904 (2011). [I.F: 2.286]
12. R. Thiyagarajan, U. Devarajan et al, J. Appl. Phys. 110, 093905 (2011). [I.F: 2.286]
GRANT DETAILS
1. Post-Doctoral Project (Ongoing) - Funded by DSKPDF Scheme, MHRD-UGC.
Total cost of project: Rs. 25.32 Lakhs
Title: Synthesis, characterization and investigation of Oxides, alloys under extreme conditions for magnetic refrigeration applications.
Research Mentor : Dr. C. Venkateswaran, Professor & Head, Department of Nuclear Physics, University of Madras, Guindy Campus, Chennai- 600 025
2. Post-Doctoral Project (Completed) -Funded by SERB-NPDF (August 2016-August 2018) as a Principle Investigator.
Total cost of project: Rs. 19.2 Lakhs
Title: Synthesis, characterization and investigation of Heusler alloys under extreme conditions for magnetic refrigeration applications.
Research Mentor : Dr. Sunil Nair, Associate Professor, Department of Physics, Indian Institute of Science Education and Research, Pune – 411 008