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Veeturi Srinivas
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Veeturi Srinivas
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Veeturi Srinivas
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Srinivas, Veeturi
Srinivas, V.
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10 results
Now showing 1 - 10 of 10
- PublicationObservation of magnetic cluster phase above Curie temperature in Fe 2CrAl Heusler alloy(01-04-2012)
;Saha, Ritwik; Venimadhav, A.We present a detailed magnetic critical behavior study of Fe 2CrAl Heusler alloy, for the first time, with rigorous analysis of high precision magnetization data obtained over the critical temperature region. Our studies confirm that B2 type site-disordered in Fe 2CrAl alloy exhibits long-range ferromagnetic order below a well defined Curie temperature (T=208 K). Though the nature of this transition is found to be of second order, the estimated critical exponents β=0.42, γ=1.356 and δ=4.25, are in between the theoretically predicted values for three-dimensional Heisenberg and mean-field interaction models. However, it is noteworthy that the scaling relations are obeyed indicating renormalization of interactions around the Curie temperature (T C), where magnetization data collapse into two separate branches, above and below T C. This conclusively shows that calculated critical exponents as well as critical temperature are unambiguous and intrinsic to the system. However, magnetization vs temperature data shows another magnetic transition (at T=313 K) above the Curie temperature. It is shown that the short range magnetic correlation exist even beyond T C with cluster moment ∼10 2 μ B. This is attributed to a site disorder which results in formation of Cr clusters with short range ferromagnetic order. © 2011 Elsevier B.V. All rights reserved. - PublicationLow temperature magnetic and electrical transport behavior of Co 58.5 Ga 41.5 alloy(24-06-2015)
;Yasin, Sk Mohammad ;Saha, Ritwik ;Rao, T. V.Chandrasekhar; ; Nigam, A. K.The electrical transport and magnetic properties of Co 58.5 Ga 41.5 binary alloy have been investigated in the temperature range 2-300 K. Analysis of field and temperatures dependence magnetization data suggests a reentrant magnetic behavior with Curie temperature (T C ) ∼90 K. Temperature dependence of resistivity shows large residual resistivity values which is sensitive to the applied magnetic field. The temperature and field dependent resistivity behavior indicates the presence of spin fluctuations at low temperature. Magnetoresistance (MR) of 17 % has been observed at 2 K in 90 kOe field, which follows a power law with exponent varying form 0.5 at low temperature to linear behavior at higher temperature. The temperature variation of magnetization and MR can be understood on the basis of ferromagnetic matrix with finite spin clusters. - PublicationMagnetization and magneto-transport studies on Fe2VAl1-xSix(08-07-2015)
;Amaladass, E. P. ;Satya, A. T. ;Sharma, Shilpam ;Vinod, K.; ;Sundar, C. S.Bharathi, A.Abstract We report on magnetoresistance, Hall and magnetization measurements of Fe2VAl1-xSix Heusler compounds for x = 0.005, 0.015, 0.02. There is a systematic change in the temperature coefficient of resistance (TCR) from negative to positive as the Si composition is increased. The Hall co-efficient shows that the carriers are electron like and the carrier density increases with Si concentration. Resistance measurements under magnetic field indicate a decreasing behavior under the application of magnetic field at low temperature region (T < 60 K), suggesting the suppression of scattering by magnetic field. Temperature and field dependent magnetization measurements did not show any significant change apart from the fact that the presence of super paramagnetic (SPM) cluster and its ordering at low temperatures. Arrott plot analysis of magnetization versus field also indicates the magnetic ordering with applied field below 60 K. - PublicationEffect of chemical disorder on Griffiths phase in weak itinerant ferromagnetic Ni92−xCuxCr8 alloy(05-12-2022)
;Vishvakarma, Sonu; ;Khanna, D. L.R.Pérez-Landazábal, J. I.We report magnetic and thermal properties of Cu substituted Ni92−xCuxCr8 polycrystalline alloys close to their critical concentration (xc ~18%), where ferromagnetic order disappears. From the detailed analysis of field and temperature dependent magnetization data weak itinerant ferromagnetic character has been identified for the compositions below xc. Spin-fluctuations theory using the Ginzburg–Landau formalism further revealed the contributions of spin fluctuations, which increase near xc. Specific heat data shows unusual low-temperature variation with an enhanced Sommerfeld coefficient and non Fermi-liquid behavior due to strong magnetic fluctuations near xc. The magnetization data and the linear term of the specific heat follow the theoretical predictions of a ferromagnetic quantum critical point within the experimental uncertainties. The exponent of the power-law M(H) ∝Hλ fits to low-temperature magnetic isotherms and its variation with composition indeed suggests a possibility of quantum Griffiths phase in these alloy compositions. Finally, this study shows that the Cu substituted Ni-Cr system shows Griffiths phase at critical point even after the reduction of disorder. - PublicationEffect of Ni substitution and annealing temperature on structural and magnetic properties of MnZn-Ferrites: Cytotoxicity study of ZnO and SiO2 coated core shell structures(15-12-2022)
;Mallesh, Shanigaram ;Mondal, Pradip ;Kavita, Srikanti; Nam, Young WooMagnetic spinel ferrite nanoparticles (NPs) have a broad scope of applications based on their structural properties, including in lithium-ion batteries, catalysts, electrochemical energy storage, drug delivery, magnetic hyperthermia, and photothermia. In this study, we investigated the structure, crystallographic phase formations, and magnetic properties of Ni-substituted MnZn ferrites (MZFs), Mn(0.6-x)Zn(0.4-y)Ni(x+y)Fe2O4 (x = 0–0.6, y = 0; y = 0–0.4, x = 0) compositions of as-prepared (AP) and air annealed (350–1200 °C) samples. All AP NPs exhibited a pure spinel structure. Ni-MZF compositions annealed at 600 °C had high α-Fe2O3 secondary phase content in Ni-MZFs (Ni substituted for Zn), whereas Ni-MZFs with x = 0.4 (Ni substituted for Mn) had no impurities, and its magnetization (50 emu/g) was enhanced compared with that of the other samples. X-ray photoelectron spectroscopy revealed that Fe3+ cations were present in tetrahedral and octahedral sites. The single spinel phase reappeared with improved crystallinity in all Ni-MZFs by annealing at 1200 °C and exhibited superior magnetization (60–73 emu/g) compared with that of MZF (35 emu/g). Additionally, the spinel phase was stabilized in the ZnO- and SiO2-coated Ni-MZF core shell structures annealed at 700 °C with higher magnetization than MZF. Moreover, Ni-MZF core shell structures exhibited biocompatibility and may have biomedical applications. - PublicationStructure and magnetic properties of ZnO coated MnZn ferrite nanoparticles(15-11-2016)
;Mallesh, Shanigaram ;Sunny, Annrose ;Vasundhara, MuttaA comparative study of structural and magnetic properties of MnZn spinel ferrite (SF) and ZnO coated MnZn ferrite (ZF) nanoparticles (NPs) has been carried out. The as-prepared NPs show a single phase cubic spinel structure, with lattice parameter ~8.432 Å. However, α-Fe2O3 impurity phase emerge from SF particles when subjected to annealing at 600 °C in air. The weight fraction of α-Fe2O3 phase increases with increasing Mn concentration (9% for x=0.2 and 53% for x=0.6). On the other hand in ZF (x=0.2 and 0.4) NPs no trace of impurity phase is observed when annealed at 600 °C. The magnetic measurements as a function of field and temperature revealed superparamagnetic like behavior with cluster moment ~104 μB in as-prepared particles. The cluster size obtained from the magnetic data corroborates well with that estimated from structural analysis. Present results on ZnO coated MnZn ferrite particles suggest that an interfacial (ZnO@SF) reaction takes place during annealing, which results in formation of Zn-rich ferrite phase in the interface region. This leads to deterioration of magnetic properties even in the absence of α-Fe2O3 impurity phase. - PublicationEvolution of ferromagnetic interactions from cluster spin glass state in Co–Ga alloy(15-11-2016)
;Mohammad Yasin, Sk ;Saha, Ritwik; ; Nigam, A. K.Low temperature magnetic properties of binary CoxGa100−x (x=54–57) alloy have been investigated. Analysis of frequency dependence of ac susceptibility provided a conclusive evidence for the existence of cluster spin glass like behavior with the freezing temperature ~8, 14 K for x=54, 55.5 respectively. The parameters for conventional ‘slowing down’ of the spin dynamics have been extracted from the acs data, which confirm the presence of glassy phase. The magnitude of Mydosh parameter obtained from the fits is larger than that reported for typical canonical spin glasses and smaller than those for non-interacting ideal superparamagnetic systems but comparable to those of known cluster-glass systems. Memory phenomena using specific cooling protocols also support the spin-glass features in Co55.5Ga44.5 composition. Further the development of ferromagnetic clusters from the cluster spin glass state has been observed in x=57 composition. - PublicationAnomalous magnetic behavior in Ni80Cr20 nanoparticles prepared by physical and chemical methods(01-09-2021)
;Vishvakarma, Sonu; ;Ranjan, PremWe report a detailed study of the structural and magnetic properties of Ni80Cr20 fine particles prepared by physical methods, such as mechanical alloying, wire explosion process (WEP), and chemical methods like sodium borohydride reduction, polyol method. From the analysis of structural and microstructural data, phase formation with the desired composition is confirmed in the particles prepared by the WEP. A comparative study of magnetization data of bulk and nanoparticles of Ni80Cr20 suggests that a weak magnetic moment develops in nanoparticles due to finite-size effects. Analysis of magnetization data suggests a superparamagnetic (SPM) behavior in the smallest sized (34 nm) particles prepared by WEP, while nanoparticles prepared by other methods show ferromagnetic ground state. Further, it is shown that the origin of weak magnetic moment and development of SPM state in the nanoparticles is due to uncompensated surface spins with a negligible interaction effect. - PublicationLow-temperature magnetization behaviors of superparamagnetic MnZn ferrites nanoparticles(01-04-2020)
;Mallesh, Shanigaram; ;Vasundhara, M.Kim, Ki HyeonHere, we report microstructure and magnetic properties of MnxZn1-xFe2O4 (x = 0–1) nanoparticles synthesized by sol-gel method. From microstructure studies, it is confirmed that all compositions of the present study exhibited a pure cubic spinel ferrite phase with narrow particle size distribution with an average particle size between 13 and 20 nm. From the temperature and magnetic field dependence magnetization data, a superparamagnetic (SPM)-like behavior is seen with a large magnetic moment (~104 μB) in particles. From the analysis of the difference in field-cooled and zero-field-cooled magnetization data, which presented a distribution of blocking temperatures which in turn supported the microstructural data. Further, the analysis of the thermoremanence magnetization data reveals the activation resulting from multiple anisotropy energy barriers due to the size distribution of the particles. The results obtained from the memory effect studies on temperature dependent magnetization in field-cooled and zero-field-cooled protocols confirm the SPM behavior of the particles. - PublicationA comprehensive study on thermal stability and magnetic properties of MnZn-ferrite nanoparticles(01-04-2019)
;Mallesh, S.Nanoparticles of MnxZn1-xFe2O4 (0 ≤ x ≤ 1.0) compositions were synthesized via sol-gel process. The structure, thermal stability and magnetic properties of as-prepared and annealed samples have been investigated. Although, as-prepared and 1200 °C air annealed samples exhibit cubic spinel ferrite phase, they decompose into α-Fe2O3, or/and α-Mn2O3 phases along with the poor quality of ferrite phase on annealing at 600 °C in air. Present investigations show that the stability of spinel ferrite phase is sensitive to (i) Mn concentration (ii) the annealing temperature and (iii) environments (air, Oxygen and Argon atmosphere) in which annealing experiments were carried out. A comparative study of structural and magnetic properties of Argon and air annealed samples suggest that differential oxygen partial pressure plays a significant role in stability as well as magnetic properties. Therefore, we suggest the deterioration of magnetic properties in Mn-Zn ferrite nanoparticles is due to depletion of Fe3+ ions from spinel structure that affects the cation distribution. It is also shown that magnetic properties can be tuned by controlling the process conditions. From these studies we propose a phenomenological model which explains the observation of present study.