Institute Ciencias Tecnologicas e Exatas

Uberaba, Brazil

Institute Ciencias Tecnologicas e Exatas

Uberaba, Brazil
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Gadioli G.Z.,University of Campinas | Rouxinol F.P.,University of Campinas | Gelamo R.V.,Institute Ciencias Tecnologicas e Exatas | Cardoso L.P.,University of Campinas | And 2 more authors.
Thin Solid Films | Year: 2013

Investigations of magnetic phases, transition temperatures and coercivity were performed in multilayered Gd/Cr films as a function of the crystalline state and morphology of the Gd layers.The films were deposited by dc magnetron sputtering at three substrate temperatures, Ts, (room temperature, 300 and 500 C).The Gd and Cr thicknesses were of 10 and 30 nm, respectively.Two series of three films were prepared.In one of the series, the films had a single Gd/Cr bilayer; in the other, 15 bilayers.The discontinuous or granular nature of the Gd layers was revealed by scanning electron microscopy Grazing incidence angle x-ray diffraction was used to investigate the crystalline state of the Gd and Cr layers.These techniques revealed that grain average size and crystalline order increase with increasing Ts.From dc magnetic measurements, the co-existence of ferromagnetic and superferromagnetic phases in the Gd layers was observed, and Curie transition temperatures, TC, were determined.High coercive fields at low temperature (2 K) were measured in hysteresis cycles.Field-cooled and zero field-cooled magnetizations as functions of temperature curves exhibited, for some of the samples, a low temperature peak suggesting a freezing transition to a cluster glass state.This was confirmed by complementary ac-susceptibility measurements carried out as a function of temperature, for various frequencies of the ac field.Some results of this work - the decline in TC for decreasing Gd grain size, the high coercive field and its dependence on particle size, and the behavior of the magnetization at low temperatures for the sample deposited at room temperature - are discussed in terms of finite size and surface effects in nanosized particles.© 2013 Elsevier B.V.All rights reserved.

Patil U.V.,CSIR - National Chemical Laboratory | Pawbake A.S.,CSIR - National Chemical Laboratory | Pawbake A.S.,University of Pune | Machuno L.G.B.,Institute Ciencias Tecnologicas e Exatas | And 4 more authors.
RSC Advances | Year: 2016

We report here the effect of plasma treatment on multilayer graphene samples as determined by X-ray photoelectron spectroscopy and surface morphology studies with atomic force microscopy, scanning electron microscopy and transmission electron microscopy. The plasma treatment was modified to introduce controlled levels of defects and functionalities to the graphene samples to give tunable properties. The elemental composition and structure were investigated by XPS and micro Raman spectroscopy. The XPS study showed that there was a slight variation in the sp2/sp3 hybridization ratio between the plasma-treated samples and the pristine sample. Kelvin probe measurements were carried out on all the multilayer graphene samples and indicated a slight variation in the work function of the graphene samples after plasma treatment. © 2016 The Royal Society of Chemistry.

Naik K.K.,Indian Institute of Technology Bhubaneswar | Khare R.T.,University of Pune | Gelamo R.V.,Institute Ciencias Tecnologicas e Exatas | More M.A.,University of Pune | And 3 more authors.
Materials Research Express | Year: 2015

Electron emission properties of electrodeposited spinel NiCo2O4 nanosheet arrays grown on Ni foam have been studied. The work function of NiCo2O4 was calculated by density functional theory using the plane-wave basis set and used to estimate the field enhancement factor. The NiCo2O4 nanosheet arrays exhibited a low turn-on field of 1.86 V μm.1 at 1 μA cm-2 and current density of 686 μA cm-2 at 3.2 V μm-1, with field enhancement factor β.=.1460 and good field emission current stability. The field emission properties of the NiCo2O4 nanosheet arrays showed enhanced performance compared to chemically prepared NiCo2O4 nanosheets. Hence, the nanosheet arrays have great potential as robust high performance vertical structure electron emitters for future flat panel displays and vacuum electronic device applications. © 2015 IOP Publishing Ltd.

Khare R.T.,University of Pune | Gelamo R.V.,Institute Ciencias Tecnologicas e Exatas | More M.A.,University of Pune | Late D.J.,CSIR - National Chemical Laboratory | Rout C.S.,Indian Institute of Technology Bhubaneswar
Applied Physics Letters | Year: 2015

Electron emission properties of multilayer graphene (MLG) prepared by a facile exfoliation technique have been studied. Effect of CO2 Ar, N2, plasma treatment was studied using Raman spectroscopy and investigated for field emission based application. The CO2 plasma treated multilayer graphene shows an enhanced field emission behavior with a low turn on field of 0.18 V/μm and high emission current density of 1.89 mA/cm2 at an applied field of 0.35 V/μm. Further the plasma treated MLG exhibits excellent current stability at a lower and higher emission current value. © 2015 AIP Publishing LLC.

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