Browsing by Author "P.S. Pandey"

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A study on swift (∼100 MeV) heavy ion irradiated Ni films on Si substrates
(2007) J.K. Tripathi; P.S. Pandey; P.C. Srivastava
Ni thin films (∼50 nm) on silicon substrates have been irradiated from 100 MeV swift heavy ions of Fe7+ with a fluence of 1012 ions cm-2. SEM studies show a nice feature of interwoven grains which looks like a knitted network which has been resolved as a spherical grainy structure from AFM studies. Chemical phase identification of the grains has been done from XRD studies and it is found that there is a formation of the Ni2Si silicide phase having average grain size of ∼70 nm. The devices have also been characterized from I-V characteristics before and after the irradiation at varying temperature from LN2 to room temperature. The current across the irradiated interface has increased by two orders of magnitude as compared to the unirradiated ones and show a nearly temperature independent behaviour. MR (magnetoresistance) has been studied from the current flow data in magnetic fields up to 10 kG. Unirradiated devices do not show any effect on current transport in external magnetic field. M-H characteristics of the irradiated devices show the typical magnetic behaviour of nano particles like superparamagnetic behaviour. The MR features has been related to the M-H variations. The observed results show the formation of magnetic nano grains due to interfacial intermixing in these devices of Ni/n-Si. The role of swift heavy ions for nano grain fabrication has been discussed and the observed properties have been understood by considering the formation of a nano magnetic granular phase. © 2007 Elsevier B.V. All rights reserved.
AFM and electronic transport studies of swift heavy ion irradiated Mn/p-Si bilayer structure
(Elsevier, 2008) P.C. Srivastava; M.K. Srivastava; P.S. Pandey
Mn/p-Si structures have been realised by electron beam evaporation of manganese on etched and cleaned p-Si wafers. Bilayer structures have been irradiated by swift heavy ions (of 100 MeV Fe7+ having a fluence of 1 × 1013 ions/cm2). The electronic transport features across the bilayer of the structure (i.e. I-V characteristics across the Mn/p-Si interface) show a significant increase of current (by two orders of magnitude) for the irradiated ones as compared to un-irradiated ones. I-V characteristics across the interface has also been recorded in presence of in-plane (i.e., along the plane of the interface) magnetic field which show a significant magnetic field sensitivity for the irradiated ones. The surface morphological studies from AFM show a granular structure with open face having micro-particles in it, prior to the irradiation and round shaped embedded granular structure after the irradiation. XRD data show the formation of manganese silicide (Mn5Si2). The results are understood in the realm of interfacial intermixing which is tailored by the swift heavy ion irradiation. © 2008 Elsevier B.V. All rights reserved.
Electronic flow across swift (∼100 MeV) heavy ion irradiated Fe/Si interfaces
(2004) P.C. Srivastava; P.S. Pandey; J.K. Tripathi
The current flow across Fe/Si interface devices has been studied after swift (∼100 MeV) heavy ion irradiation. The current flow has been also studied in a low magnetic field of <1 KG. It has been observed that the current flow in such devices increases substantially (by two orders of magnitude) after irradiation and shows a strong effect in the magnetic field. The current flow through the devices has been found to be temperature-independent from liquid nitrogen temperature to room temperature. The scanning electron microscopy and x-ray diffraction features show a mixed phase of iron silicide (FexSiy) with an average grain size of ∼200 nm. It seems that a Fe/FexSiy/Fe tunnel junction is formed at the irradiated Fe/Si interface resulting in the observed features. Moreover, the magnetic interlayer coupling at the interface seems to control the effect of the magnetic field on current flow through the reacted (or mixed) interface.
Irradiation induced modifications in magnetic property of Mn/n-Si structure
(Institute of Physics Publishing, 2011) M.K. Srivastava; P.S. Pandey; P.C. Srivastava
Mn films of ∼50 nm were deposited on n-Si (100) substrates by electron beam evaporation technique. The Mn/n-Si structures were irradiated from swift heavy ions with a fluence of 1×1013 ions/cm2. The irradiated and unirradiated structures have been characterized from atomic force microscopy, X-ray diffractometry and vibrating sample magnetometer facilities. It has been found that surfacial/interfacial granular magnetic silicide phases (of MnxSiy) are formed before and after the irradiation with irradiation induced modifications of surface morphology and magnetic property. The surface roughness has been found to decrease on the irradiation from the atomic force microscopy data. From the X-ray diffraction data, it has been found that after the irradiation MnSi is formed in addition to Mn 5Si2 as compared to unirradiated ones. The magnetization characteristics show that the magnetic parameters such as coercivity, saturation magnetization, remanance and squareness have decreased on the irradiation for in-plane orientation whereas coercivity and remanance is increased after the irradiation for out of plane orientation. The increase of remanance shows the presence of strong exchange coupling in the structure after the irradiation. © Published under licence by IOP Publishing Ltd.
Irradiation induced modifications in microstructural and magnetic property of Fe 50Ni 50 (permalloy)/Si interfacial structure
(2014) P.C. Srivastava; P.S. Pandey; Neelabh Srivastava; M.K. Srivastava
The interfacial structures of Fe50Ni50/Si have been prepared by electron beam evaporation of the alloy on silicon substrates. X-ray diffraction data confirm the formation of the alloy phase of Fe50Ni50 and intermixed silicide phases of Fe5Si3, Ni3Si2, Ni2Si and NiSi. The structures have also been irradiated from swift heavy ions to study the effect of irradiation induced interfacial intermixing. Magnetic force microscopy (MFM) and magnetisation characteristics have been used to characterise the magnetic behaviour of as-prepared and irradiated structures. It is observed from the MFM that the magnetic domains are of sub-micron scale and there is a significant magnetic signal from the surface of the structure which becomes stronger for the irradiated structures. The observed magnetisation (M-H) characteristics show the presence of in-plane and out-of-plane magnetic anisotropy in the structure which has been observed to be removed on the irradiation. The magnetisation characteristics has been understood as the magnetic behaviour of nano-magnetic grains of silicides (and of the alloy, Fe50Ni50) which are formed as a result of interfacial chemistry and modified by irradiation induced interfacial intermixing. The observed magnetic behaviour seems interesting and significant for many applications related to magnetics. © 2013 © 2013 Taylor & Francis.
Magnetic and semiconducting nanostructures by swift heavy ion irradiation of Fe20Ni80 films on Si substrates
(2005) P.C. Srivastava; J.K. Tripathi; P.S. Pandey
Fe20Ni80/Si interface devices have been fabricated and irradiated from swift (100 MeV) heavy (Fe7+) ions with a dose of 1014 cm-2. The current measured across the irradiated devices from room temperature (RT) to liquid nitrogen (LN2) temperature shows a positive temperature coefficient. The results were understood by considering the formation of a semiconducting and magnetic silicide nanophase as a result of ion beam mixing (which was shown from x-ray diffraction (XRD) data). The particle size was estimated to be ∼25 nm from the XRD data. The induced magnetization at the interface was studied from the magnetization versus magnetic field (M-H) variation at room temperature. The magnetization shows superparamagnetic behaviour characterizing the magnetic nanoparticles. © 2005 IOP Publishing Ltd.
Nano granular magnetic phase by interfacial intermixing in Fe 50Ni50/Si
(2010) P.C. Srivastava; P.S. Pandey
The bilayer structures of Fe50Ni50 films on silicon substrate have been studied before and after the swift (∼100 MeV) Fe 7+ ion irradiation. The AFM (atomic force microscopy) study of the structures shows the formation of clear ellipsoidal grains of nano dimensions. XRD (X-ray diffraction) data of the structures show the formation of magnetic silicide phases of Fe5Si3, Ni3Si2 and Ni2Si. Electronic flow across the interface has been found to significantly increase by two orders of magnitude on the irradiation. Moreover the electronic flow shows a low magnetic field (of ∼500 G) sensitivity for the irradiated structures and not for the unirradiated ones. The M-H (magnetization versus magnetic field) characteristics show the typical behaviour of nano magnetic grains which are antiferromagnetically coupled in a paramagnetic phase. The observed results have been understood in the realm of interfacial intermixing (which has been further tailored by the irradiation) to result the nano granular phases of magnetic silicides (of ∼50 nm). The intermixing seems to make the interface intimate enough to result in a significant increase of current across interface of the bilayer and its sensitivity for an in plane low magnetic field. © 2010 Elsevier Ltd. All rights reserved.