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Harish Kumar N
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Harish Kumar N
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Harish Kumar N
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Kumar, Narayanan Harish
Kumar, N. H.
Harish Kumar, N.
Harishkumar, N.
Kumar, N. Harish
Narayanan, Harish Kumar
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30 results
Now showing 1 - 10 of 30
- PublicationMagnetoresistance studies of Ho0.85Tb0.15Mn2-xFex (x=0, 0.25, 0.5, 1, and 2)(01-09-2005)
;Chelvane, J. Arout; ; ; Malik, S. K.Magnetoresistance (Δρ ρ) studies have been carried out on the C15-type cubic Laves phase Ho0.85Tb0.15Mn2-xFex (x=0, 0.25, 0.5, 1, and 2) compounds up to a magnetic field of 90kOe at temperatures 5, 30, and 100K. The lattice parameters were found to decrease with increasing x. The Curie temperature is found to increase with increasing x from 30to680K, which is attributed to the net increase in the exchange splitting of the spin-up and spin-down bands. A maximum value of Δρ ρ of -27% was observed for Ho0.85Tb0.15Mn2 around the ordering temperature. This is explained on the basis of nearest Mn-Mn critical distance. A positive magnetoresistance, increasing in a discontinuous manner with increasing field, due to the dependence of scattering of conduction electrons on large magnetoelastic interactions, was observed at 5K in Ho0.85Tb0.15Fe2. © 2005 The American Physical Society. - PublicationMagnetic and electrical properties of Ho0.85Tb 0.15Mn2 and Ho0.85Tb0.15Fe 2(01-03-2006)
;Chelvane, J. Arout; ; ; Malik, S. K.Magnetization and magnetoresistance studies have been carried out on Ho0.85Tb0.15Mn2 and Ho0.85Tb 0.15Fe2. The saturation magnetization of Ho 0.85Tb0.15Mn2 is found to be large compared to Ho0.85Tb0.15Fe2. A large negative magnetoresistance of 27% was observed for Ho0.85Tb 0.15Mn2 around the ordering temperature. In the paramagnetic region, a positive magnetoresistance at lower magnetic fields and negative magnetoresistance is at higher magnetic fields have been observed for Ho0.85Tb0.15Mn2. A positive magnetoresistance of 3.5% with a step-like behavior has been observed for Ho0.85Tb 0.15Fe2 at 5 K. © 2005 Elsevier B.V. All rights reserved. - PublicationCoexistence of cluster ferromagnetism and cluster spin-glass like behaviour in melt-quenched Cu2Mn0.5Fe0.5Al Heusler alloy(10-03-2019)
;Venkateswarlu, B. ;Hari Krishnan, R. ;Arout Chelvane, J. ;Babu, P. D.We investigated the structural stability and magnetic properties of the melt-quenched Heusler alloy-Cu2Mn0.5Fe0.5Al using X-ray diffraction (XRD), scanning electron microscopy (SEM), dc magnetization and ac susceptibility measurements respectively. The structural analysis by Rietveld refinement showed that the alloy crystallised in L21 structure with no trace of secondary phase in the XRD pattern. The dc magnetic measurements exhibited a thermal irreversibility between field-cooled (FC) and zero field cooled (ZFC) magnetization curves at an irreversible temperature Tirr. A deviation from de Almeida –Thouless like line for Tirr vs. H data was observed, suggesting a possibility of cluster glass (CG) like phase in the sample. To confirm the CG behaviour, frequency dependent ac susceptibility (χac) measurements were carried out on the sample and was analysed by Vogel-Fulcher (VF) and Critical slowing down models. We obtained large relaxation time constants (τ0) from the fit to both the phenomenological models which indicate that the origin of glassy nature may not be from randomly oriented atomic spins like in spin-glasses (SG) but of magnetic clusters. The analysis of nonlinear susceptibilities of the sample confirmed the coexistence of ferromagnetic interactions and glassy nature in the sample. Further confirmation for the glassy nature in the sample was provided by ZFC memory experiments. No anomaly was found corresponding to long-range order in the heat capacity (CP(T)) measurement and a T3/2 dependence was also seen in the electrical resistivity which indicates the magnetic glassiness in the sample. - PublicationEffect of W co-doping on the optical, magnetic and electrical properties of Fe-doped BaSnO 3(01-07-2012)
;Balamurugan, K.; ;Arout Chelvane, J.The effect of W co-doping on the optical, magnetic and electrical properties of Fe-doped BaSnO 3 has been studied. Polycrystalline BaSnO 3, BaSn 0.96Fe 0.04O 3 and BaSn 0.95Fe 0.04W 0.01O 3 samples were prepared using solid state reaction. In the analysis of powder X-ray diffraction patterns, the samples were found to be free of secondary phases. Diffuse reflectance spectra evidenced the substitution of Fe and W for Sn in the host BaSnO 3. Micro-Raman spectra confirmed the existence of oxygen vacancies in the samples. Upon W-1% co-doping, the ferromagnetic character of Fe-4% doped BaSnO 3 is suppressed drastically and its Curie temperature is reduced to 310 K from 462 K. The existence of F-centers and ferromagnetic interactions at room temperature is evidenced by the electron paramagnetic resonance and ferromagnetic resonance signals observed in the electron spin resonance spectra of the undoped and Fe-4% doped, (Fe-4% and W-1%) co-doped BaSnO 3 samples respectively. Suppression of ferromagnetism upon W co-doping is due to the fact that each W 6 ion donates two electrons to the host lattice and it reduces the number of oxygen vacancies that are essential for ferromagnetism to exist in the Fe-doped BaSnO 3 samples. © 2012 Elsevier B.V. All rights reserved. - PublicationHalf metallic Co2TiGea theoretical and experimental investigation(01-01-2011)
;Prathiba, G. ;Venkatesh, S. ;Rajagopalan, M.Using first principle calculations the electronic structure and magnetic properties of the half metallic Co2TiGe was investigated. The electronic structure calculations were performed using two different parameterization schemes. The band gap obtained in the minority spin state using LDA scheme in TB-LMTO method was smaller than that obtained using GGA scheme in FP-LAPW method. To explore the half metallic property experimentally bulk Co2TiGe was synthesized by arc melting under argon atmosphere. The magnetic moment per formula unit determined from saturation magnetization at 2 K was 1.9 μB, which was close to the theoretically calculated value of 2 μB. A detailed analysis of the low temperature transport and magnetotransport properties exhibit characteristic features of half metals such as T9/2 dependence of low temperature resistivity, negligible temperature dependence of resistivity below 20 K and a cross over from positive to negative MR around 100 K. © 2010 Elsevier B.V. All rights reserved. - PublicationInvestigation of atomic anti-site disorder and ferrimagnetic order in the half-metallic Heusler alloy Mn 2V Ga(22-08-2012)
;Kumar, K. Ramesh; ;Babu, P. D. ;Venkatesh, S.Ramakrishnan, S.The band structure calculation for the compound Mn 2VGa carried out using the plane wave self-consistent field package with generalized gradient approximation shows that the compound is nearly half-metallic at the equilibrium lattice parameter. However, theoretical investigations have shown that a certain percentage of atomic anti-site disorder can destroy the half-metallic nature of the sample. Hence it is important to quantify the site disorder in these systems. We have deduced the percentage of atomic anti-site disorder from the refinement of the higher angle room temperature (300K) neutron diffraction (ND) pattern and it was observed to be roughly 8% in our sample. The field variation of resistance recorded at different temperatures shows a positive slope at low temperatures and a negative slope at higher temperatures, indicating the half-metallic character at low temperatures. The abinitio calculations predict a ferrimagnetic ground state for this system. The analysis of the magnetic structure from ND data measured at 6K yields magnetic moment values of 1.28μ B and 0.7μ B for Mn and V, respectively, confirming the ferrimagnetic ordering. © 2012 IOP Publishing Ltd. - PublicationRoom temperature ferromagnetism in Fe-doped BaSnO3(20-03-2009)
;Balamurugan, K.; ;Chelvane, J. AroutPolycrystalline bulk samples of BaSn1-xFexO3, with x = 0.03, 0.04 and 0.05 were prepared by solid-state reaction method. These Fe-doped BaSnO3 systems exhibit ferromagnetism at room temperature with an average magnetic moment of 0.047, 0.038 and 0.025μB/Fe and Curie temperature of 510, 462 and 446 K, respectively. The observed magnetic properties are not attributed to any of the known impurity phases or clusters. The presence of ferromagnetic interaction at room temperature is supported by the ferromagnetic resonance (FMR) signals observed in the electron spin resonance spectra. The ferromagnetic order between Fe-ions is expected to be mediated by an electron trapped at the oxygen anion vacancy, called the F-centre exchange (FCE) interaction. © 2008 Elsevier B.V. All rights reserved. - PublicationComplex magnetic behavior of the heusler alloy - Cu2Mn0.75Fe0.25Al(01-11-2014)
;Venkateswarlu, Buchepalli ;Babu, P. D.We investigated the structural and magnetic properties of Cu2Mn1-xFexAl (x =0.25 , 0.5, 0.75) alloys. Among the three compositions, only x =0.25 composition crystallizes in single phase with L 21 structure but its magnetic response indicates a complex magnetic structure. The magnetic isotherms were fitted to modified Langevin equation which indicates the presence of clusters with large magnetic moment. The ac susceptibility studies showed the presence of a superparamagnetic phase in the system over and above ferromagnetic order. To determine the nature of the interactions among the clusters, the variation of freezing temperature (Tf) with applied ac frequency was analyzed using different models (Néel-Arrhenius, Vogel-Fulcher, and critical slowing down model). - PublicationMn2V0.5Co0.5Z (Z = Ga, Al) Heusler alloys: High TC compensated P-type ferrimagnetism in arc melted bulk and N-type ferrimagnetism in melt-spun ribbons(01-11-2019)
;Midhunlal, P. V. ;Arout Chelvane, J. ;Prabhu, D. ;Gopalan, RaghavanFerrimagnetic Heusler alloys with the low moment and high Curie temperature are desired material for spintronic devices utilizing spin transfer torque phenomena. Our earlier report showed compensated ferrimagnetism with high Curie temperature in arc melted bulk Mn2V0.5Co0.5Z (Z = Ga, Al) alloys. The low-temperature M-T behaviour of the bulk alloys was not explored and in this report we discuss the structural and magnetic properties of Mn2V0.5Co0.5Z (Z = Ga, Al) Heusler alloys in the ribbon and bulk forms, particularly concentrating on the distinct low-temperature M-T behaviour. The observed magnetic moment of the parent alloys is around 2 μB/f.u. which was reduced to nearly zero as the Co is substituted at the V site of the Mn2VZ (Z = Ga, Al) alloys. The compensated moment value at room temperature for Mn2V0.5Co0.5Ga alloy in the bulk and ribbon forms are 0.13 and 0.09 μB/f.u. respectively. For Mn2V0.5Co0.5Al, a further reduced moment was observed which are 0.08 and 0.04 μB/f.u for the bulk and ribbon samples respectively. The observed Curie temperatures are more than 640 K for both ribbons and bulk samples. A very different temperature dependent magnetic response was observed for the ribbon and bulk samples. The arc melted bulk samples exhibited Néel P-type ferrimagnetic behaviour where there is no full compensation temperature. In contrast to this, the ribbon samples exhibited Néel N-type ferrimagnetic behaviour with a full compensation temperature of 420 K for Mn2V0.5Co0.5Ga and 275 K for Mn2V0.5Co0.5Al. - PublicationMagnetic and transport properties of transparent SrSn0.9Sb 0.05Fe0.05O3 semiconductor films(01-04-2011)
;Prathiba, G. ;Venkatesh, S. ;Kamala Bharathi, K.The effect of antimony doping on the structural, magnetic, and electrical properties of transparent SrSn0.9Sb0.05Fe 0.05O3 films synthesized by RF sputtering on oxidized Si and quartz substrates has been investigated. A reduction in electrical resistivity by two orders of magnitude compared to 5 Fe doped SrSnO3 film was observed. The electrical conductivity behavior has been analyzed using the Mott's Variable range hopping model. The nature of magnetic ordering were investigated by field cooled (FC) and zero field cooled (ZFC) magnetization measurements. The applicability of models based on oxygen vacancies to explain the magnetic ordering present in the sample has been discussed. © 2011 American Institute of Physics.
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