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We report the superconducting properties of Aluminium (Al) wires deposited on different substrates. The substrates selected are the band insulator of SrTiO3 (STO) and the 2DEG system of LaAlO3/SrTiO3 (LAO/STO). Al wires were prepared from the respective films using focused ion beam assisted milling. A significant reduction in the superconducting transition temperature was observed with respect to a control Al film which was deposited on SiO2/Si substrate. The superconducting transition temperature of Al wire on STO substrate is 0.36 K, while that of LAO/STO substrate is 0.66 K. The temperature dependent critical current follows the classical Ginzburg-Landau formulation but with slightly varying exponent values compared to the value of 3/2 corresponding to a film in the clean limit.

Space Charge Limited Conduction (SCLC) controlled BaTiO3 (BTO) hetero-junctions such as BTO/Nb:SrTiO3 (Nb:STO), BTO/La0.67Ca0.33MnO3 (LCMO), and BTO/LaNiO3 (LNO) were found to show large variation (more than one order of magnitude) in trap densities. In this paper, we show that this effect is related to epitaxial strain introduced in the film due to different bottom layer. The in-plane (a) and out-of plane (c) lattice parameters were extracted out from X-Ray diffraction scans. While all three bottom electrodes (LNO, LCMO, and Nb:STO) introduces compressive strain highest was from LNO. Consequently, the out-of-plane lattice parameter (c) was found to be higher than bulk BTO while reduction in the in-plane lattice parameter (a) was observed. In addition, grain size was also calculated and plotted against strain which shows decreasing trend with increasing strain. Furthermore, the trap density (Nt) was also presented as a function of strain displaying increasing trend with increasing strain indicating creation of more number of traps with increasing strain.

We report on broadband ferromagnetic resonance spectroscopy studies of permalloy (Py) thin films grown on large area pulse laser deposited MoS2. We observe an enhancement of the effective damping constant of the Py layer grown on few-layer MoS2. The spin mixing conductance is found to be an order of magnitude larger in the case of 3.5 (average of the 3–4 layer)-layer-MoS2/Py compared to the case of 2-layer-MoS2/Py. The results are interpreted as a consequence of the extrinsic defect induced spin-orbit coupling at the 3.5-layer-MoS2/Py interface evidenced by a higher variation of Raman intensity across the sample as compared to the 2-layer-MoS2/Py system.

We report the charge transport mechanism in BaTiO3 (BTO) thin film deposited on LaNiO3 (LNO) buffer layer using pulsed laser deposition technique thus, forming the metal – insulator – metal junction (Au/BTO/LNO). The temperature dependent Current density- Voltage (J-V) characteristics were measured, analyzed and compared with the La0.67Ca0.33MnO3 (LCMO) buffered BTO film (Au/BTO/LCMO). Although the mechanism was found to be space charge limited conduction (SCLC) as in case of BTO/LCMO but the absence of Ohmic region in Log J-Log V plot indicates higher injection rate. Various parameters such as trap density, activation energy, and ratio of free to trapped carriers (θ) were extracted out from the fitted J-V plot and subsequently their temperature dependence was studied and compared with BTO/LCMO. Higher current density, lower activation energy, lower trap density and higher ratio of free to trapped carriers (θ) were observed in BTO/LNO in contrast to BTO/LCMO. Furthermore, the lower activation energy indicates the presence of shallow trap level.

Double perovskites have been studied extensively in the bulk form however very few reports are available on their thin films. Here we are presenting results on first time grew thin films of double perovskite Nd2NiMnO6 (NNMO). We report the comparative structural and magnetic studies of the PLD grown thin films on different substrates i.e. SrTiO3 (STO) and MgO. X-ray diffraction (XRD) profiles show that the film grown on STO is epitaxial whereas it is polycrystalline on MgO substrate. Films on both the substrates were grown at 800 mTorr and 200 mTorr oxygen partial pressure. We observe that the film shows the magnetic behavior similar to the bulk sample. We observe the high-temperature ferromagnetic transition near 192 K along with an additional transition observed in the low temperature region (vicinity of 100 K) in Field cooled (FC) magnetization. Super-exchange interaction between Ni2+-O-Mn4+ is attributed to the ferromagnetic ordering in these samples. Mixed valence states Ni3+ and Mn3+ present in the films leads to antiferromagnetic (AFM) interactions which attributes to the appearance of low temperature magnetic transition. The oxygen pressure applied while growing the thin films was found to affect the magnetic moment of NNMO films significantly.

We report the electronic structure of Molybdenum disulfide (MoS2) ultrathin 2D films grown by pulsed laser deposition (PLD) on top of GaN/c-Al2O3 (0001) substrates annealed up to 550 °C in an ultrahigh vacuum. Our X-ray photoemission spectroscopy (XPS) study shows that the grown films are mixed phase character with semiconducting 2H and metallic 1T phases. After ultrahigh vacuum (UHV) annealing, the 1T/2H phase ratio is significantly modified and film-substrate bonding becomes the leading factor influencing variation of mixed phase compositions. The semiconducting phase is partially transformed to metallic phase by thermal annealing; suggesting that the metallic phase observed here may indeed have more stability compared to the semiconducting phase. The notable enhancement of the 1T/2H ratio induces significant changes in Ga 3d core level spectra taken from bare GaN and MoS2/GaN sample. The impact of S and/or Mo atoms on the Ga core level spectra is further pronounced with the thermal annealing of grown films. The analysis shows that an enhancement of 1T metallic phase with thermal annealing in MoS2 layers is manifested by the occurrence of new spectral component in the Ga 3d core level spectra with the formation of Ga-S adlayer interaction through the Ga bonding in defect assisted GaN structure.

We demonstrate the growth of ultra thin film of molybdenum disulfide on semi-insulating GaN/c-Al2O3 (0001) substrates by pulsed laser deposition. The sample was characterized by Atomic force microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. The MoS2 atomic force microscopy images show a root-mean square roughness of about 0.11 nm with some regions of clustered growth and/ or disordered surfaces. The characteristic separation between two Raman active modes has been found to be 21.6 cm-1, suggesting that the grown MoS2 film is bi-layer. Using X-ray photoelectron spectroscopic measurements, we observe the presence of mixed phase MoS2 thin film with stoichiometric mole ratio of S/Mo is about 1.85, suggesting that the film is slightly sulfur deficient under our experimental conditions.

In search of novel oxide heterostructures that display highly mobile two-dimensional charge transport at its heterointerface, we report the synthesis of non-stoichiometric perovskite CaxTayO3+δ epitaxial films on TiO2 terminated SrTiO3 (001) substrate. The layer-by-layer growth of the films was accomplished by the pulsed laser deposition (PLD) technique monitored by the in-situ Reflection high energy electron diffraction (RHEED). The experiment shows that a quasi-two-dimensional electron gas (q-2DEG) type charge transport occurs beyond 9 unit-cell of the film-thickness, with its carrier mobility ≈102 cm2/Vs.

We present the memristive (memory resistive) behavior in two different pulsed laser deposited BaTiO3/Nb doped SrTiO3 junctions. The first junction is controlled by space charge limited current (SCLC) conduction while the post-annealed junction is dominated by Schottky emission. The latter junction displays better ferroelectric and memristive properties (with an order of magnitude higher OFF/ON resistance ratio) as compared to the former junction with SCLC conduction. We attribute the improved behavior of the latter junction to the reduction of oxygen vacancies due to post-annealing of the film.

CSIR-NPL is the custodian of National standards of electrical and electronic parameters. These include DC parameters such as voltage, current and resistance; low frequency and high frequency impedance related quantities such as capacitance, inductance and AC resistance; AC/DC high voltage and AC high current; AC power and energy; and quantum standard which includes quantum hall resistance (QHR), quantum current (QC) and quantum nanophotonics (QN). The metrological traceability of the electrical and electronics parameters to SI units is derived from Josephson Voltage Standard (JVS), Quantum Hall Resistance (QHR) standard and frequency (time) standards; all of them are being maintained at CSIR-NPL with metrological precision at par with international standards. The traceability of the aforementioned parameters is disseminated through an unbroken chain of apex level calibrations and testing at par with international level to the industries and strategic sectors of the country to improve the quality of life, which in turn will lead to the inclusive growth of the country and economic development. R&D efforts on the development of quantum standards is a constant endeavour and continues to be at the forefront. Specifically, CSIR-NPL focuses on the development of quantum standards related to the unit of current (ampere), the unit of resistance (ohm) and quantum nanophotonics which aims for detection of few photons (or even single photons) using the novel concept of superconducting nanowire single photon detectors (SNSPD). Among these the research on QC needs special mention, as this will lead to realisation of the SI unit of electric current (ampere), the only unit out of the seven base units of SI system. The quantum current standard (QCS) realisation is bifurcated into two approaches, (i) based on the single electron tunnelling effect (SET) observable in semiconductor quantum dot (QD) structures and (ii) the quantum phase slip phenomenon (QPS) observable in superconducting nanowires of cross-sectional area of the order of coherence length of the system. The realisation of the resistance unit (ohm) is based on the quantum hall effect observable in semiconductor 2DEG structures such as GaAs/AlGaAs systems. Recently there has been tremendous evidence emerging for the use of monolayer graphene for the use of QHR metrology. CSIR-NPL also started the growth of “epitaxial graphene anchored on SiC” and have obtained encouraging results. The nano-photonics measurement research is also taken up actively for its applications to realize quantum standards for optical radiation and device fabrication.

Controlling spin-orbit interaction and its effect on superconductivity has been a long-standing problem in two-dimensional inversion symmetry broken superconductors. An open challenge is to understand the role of various energy scales in shaping the complex phase diagram in these systems. From a combined experimental and theoretical study of resistance fluctuations and its higher order statistics, we propose a phase diagram for the superconducting phase in the magnetic-field--spin orbit interaction energy plane for the quasi-two dimensional electron gas at the interface of LaAlO$_3$/SrTiO$_3$ heterostructures. The relative variance of resistance fluctuations increases by few orders of magnitude below the spin-orbit field B$_{SO}$ and a non-Gaussian component to the fluctuations arises for fields below the upper critical field B$_{C2}$. Theoretical calculations show that the non-Gaussian noise predominantly arises due to percolative nature of the superconducting transition. We quantify the strength and the relative importance of the spin-orbit interaction energy, Zeeman energy and the pairing potential. Our work highlights the important role played by the interplay between these energy scales in framing the fascinating phases seen in two-dimensional inversion-symmetry-broken superconductors.

One of the hallmarks of the Berezinskii-Kosterlitz-Thouless (BKT) transition in two-dimensional superconductors is the universal jump of the superfluid density that can be indirectly probed via the nonlinear exponent of the current-voltage $I\text{\ensuremath{-}}V$ characteristics. Here, we compare the experimental measurements of $I\text{\ensuremath{-}}V$ characteristics in two cases, namely NbN thin films and ${\mathrm{SrTiO}}_{3}$-based interfaces. While the former display a paradigmatic example of BKT-like nonlinear effects, the latter do not seem to justify a BKT analysis. Rather, the observed $I\text{\ensuremath{-}}V$ characteristics can be well reproduced theoretically by modeling the effect of mesoscopic inhomogeneity of the superconducting state. Our results offer an alternative perspective on the spontaneous fragmentation of the superconducting background in confined two-dimensional systems.

We report the temperature dependent current (I) – voltage (V) characteristics of Fe3O4 nanowires with varying width (w) of 132, 358, and 709 nm. While the widest nanowire (w=709 nm) shows ohmic I (V) curves for all temperatures, those for w=132 and 358 nm show nonlinearity, which can be expressed by a combination of linear (V) and cubic (V3) terms. The behaviour of conductance (linear bias component of current) and non-linearity in these nanowires is related to small polaron hopping related conduction. Moreover, we observed an anomalously large hopping lengths, which may be related to the size of percolation cluster and/or antiphase domain. Our study presents first experimental evidence for such non-linear polaronic conduction in magnetite nanowires.

This work reports a quasi-two-dimensional electron gas (q-2DEG) system at the interface of two wideband-gap insulators, (TiO2-terminated) SrTiO3 and LaScO3, with a minimum thickness of 4-unit cell (uc). The highly crystalline and abrupt heterointerface is confirmed with high-resolution electron microscopy. The mixed Ti4+ and Ti3+ valence states (for 4 uc of LaScO3) obtained from the x-ray photoelectron spectroscopy study suggest an intrinsic electronic reconstruction at the interface, leading to a metallic nature. This origin is well supported by density functional theory calculations that reveal an emergence of 3.3 states/eV/spin at the Fermi level for 4 uc in accordance with the polar catastrophe model. The study offers one more perovskite heterostructure, like LaAlO3/SrTiO3, for unraveling the q-2DEG phenomena toward a clear mechanism and futuristic applications.This work reports a quasi-two-dimensional electron gas (q-2DEG) system at the interface of two wideband-gap insulators, (TiO2-terminated) SrTiO3 and LaScO3, with a minimum thickness of 4-unit cell (uc). The highly crystalline and abrupt heterointerface is confirmed with high-resolution electron microscopy. The mixed Ti4+ and Ti3+ valence states (for 4 uc of LaScO3) obtained from the x-ray photoelectron spectroscopy study suggest an intrinsic electronic reconstruction at the interface, leading to a metallic nature. This origin is well supported by density functional theory calculations that reveal an emergence of 3.3 states/eV/spin at the Fermi level for 4 uc in accordance with the polar catastrophe model. The study offers one more perovskite heterostructure, like LaAlO3/SrTiO3, for unraveling the q-2DEG phenomena toward a clear mechanism and futuristic applications.

Multiband transport in superconductors is interesting both from an academic as well as an application point of view. It has been postulated that interband scattering can significantly affect the carrier dynamics in these materials. In this article we present a detailed study of the electrical transport properties of the high-mobility two-dimensional electron gas residing at the interface of ${\mathrm{LaAlO}}_{3}\text{/}{\mathrm{SrTiO}}_{3}$, a prototypical multiband superconductor. We show, through careful measurements of the gate dependence of the magnetoresistance and resistance fluctuations at ultralow temperatures, that transport in the superconducting regime of this system has contributions from two bands which host carriers of very different characters. We identify a gate-voltage tunable Lifshitz transition in the system and show that the resistance fluctuations have strikingly different features on either side of it. At low carrier densities, resistance noise is dominated by number-density fluctuations arising from trapping-detrapping of charge carriers from defects in the underlying ${\mathrm{SrTiO}}_{3}$ substrate, characteristic of a single-band semiconductor. Above the Lifshitz transition, the noise presumably originates from interband scattering. Our paper highlights the importance of interband scattering processes in determining the transport properties of low-dimensional systems and projects resistance fluctuation spectroscopy as a viable technique for probing the charge carrier dynamics across a Lifshitz transition.

By means of structural refinements, magnetic susceptibility measurements and density functional theory based calculations; we study the physical properties of LaCoO3 with Al substitutions. Despite Al substitutions, which result in a reduction of unit-cell volume, increased chemical disorder, and local octahedral distortions, we find that the thermally mediated low-spin and high-spin states in LaCoO3 survive against the odds. The observed relative shift of the low-spin and high-spin representative peaks in the magnetic susceptibility data is determined to be of electronic origin via a change in the material’s chemical bonding properties. Our study reveals a strong interplay between bonding and disorder for the temperature dependent spin states of LaCoO3.

Photoluminescence studies of pulsed laser deposition grown LaInO 3 thin films on TiO 2 terminated SrTiO 3 substrate showed a broad-band blue emission peaking at 412 nm, which is primarily attributed to the charge transfer transitions between oxygen and indium, inter (d–f) and intra (f–f) band transitions. The results are analysed based on the mechanism of absorption and emission within the d 10 levels of In 3+ ions. Broadening of the photoluminescence emission is observed with reduction in size of the crystallite owing to quantum confinement effects.

A rather unique feature of the two-dimensional electron gas formed at the interface between the two insulators LaAlO3 and SrTiO3 is to host both gate-tunable superconductivity and strong spin-orbit coupling. In the present work, we use the disorder generated by Cr substitution of Al atoms in LaAlO3 as a tool to explore the nature of superconductivity and spin-orbit coupling in these interfaces. We analyze the transport properties of three different samples whose only relevant difference is their elastic scattering time tau(e). A reduction of the superconducting T-c is observed with Cr doping consistent with an increase of electron-electron interaction in the presence of disorder. In addition, the evolution of spin-orbit coupling with gate voltage and Cr doping evidences a Dyakonov-Perel mechanism of spin relaxation (tau(SO) proportional to tau(-1)(e)) in the presence of a Rashba-type spin-orbit interaction.

We report the observation of a magnetic-field-assisted transient superconducting state in the two-dimensional electron gas existing at the interface of LaAlO3/SrTiO3 heterostructures. This metastable state depends critically on the density of charge carriers in the system. It appears concomitantly with a Lifshitz transition as a consequence of the interplay between ferromagnetism and superconductivity and the finite relaxation time of the in-plane magnetization. Our results clearly demonstrate the inherently metastable nature of the superconducting state competing with a magnetic order in these systems. The coexistence of superconductivity and ferromagnetism in the conducting electronic layer formed at the interface of insulating oxides has thrown up several intriguing and as yet unanswered questions. An open question in this field is the energetics of the interplay between these two competing orders and the present observation goes a long way in understanding the underlying mechanism.

We report investigations on polycrystalline LaCo1−x Al x O3 (x = 0–0.9) bulk samples. The solid state synthesized samples showed a coexistence of rhombohedral and monoclinic phases in the intermediate concentrations (0.2 ≤ x ≤ 0.5) and pure rhombohedral phase otherwise. The observed effect of Al doping on dc transport has been analysed on the basis of small polaron hopping mechanism. The magnetisation results presented give evidence of weak ferromagnetism and anomalous temperature dependence of coercivity which we associate to the canting of the localised high-spin Co(III) and anti-symmetric exchange interactions at low temperatures.

The structural transformation of electrochemically deposited Co–Cu/Cu multilayers with magnetic layer thickness was monitored via measurements of magnetization and magnetoresistance. For this, electrodeposition of [Co (tCo nm)/Cu (4 nm)]50 multilayers were carried out by varying the Co-layer thickness (tCo) down to 0.2 nm from a sulfate based single solution electrolyte. Magnetization measurements showed the appearance of anisotropy, increase in remanence magnetization and coercivity with systematic increase of tCo from 0.2 to 1 nm. Magnetic field direction dependent magnetoresistance (MR) measurements revealed that the isotropy in MR changes with tCo from tridimensional at 0.2 nm to in-plane at 0.4 nm to fully anisotropic at 1.0 nm. This illustrated that a fully granular magnetic Co-layer structure (tCo=0.2 nm) transforms into discontinuous layered one (tCo=0.4 nm) due to coalescence of suparparamagnetic regions to a continuous ferromagnetic layer (tCo=1 nm).

Electrodeposited CoCu/Cu multilayers were investigated by measuring both anisotropic magnetoresistance (AMR) and planar Hall effect (PHE) simultaneously. Studies have been carried out on a [Co(3 nm)/Cu(4 nm)]50 multilayer sample, where a maximum of −8.8 % GMR was observed at room temperature. A direct comparison of AMR and PHE output has been made both as a function of field and its relative orientation with respect to the current. Marked changes in PHE loops were observed at different angles (between magnetic field and applied current) whereas no noticeable changes could be found for AMR results. Such PHE outputs are the manifestations of complex spin reorganization due to strong antiferromagnetic-coupling between adjacent magnetic layers. In case of angular dependence output, when the applied field is less than the coercive field, the PHE output shows a deviation from the Sin2θ dependence that can be correlated to the domain wall propagation.

We probe the existence of large correlated non-Gaussian phase fluctuations in the vicinity of the superconducting phase transition in the conducting layer residing at the interface of LaAlO3/SrTiO3 heterostructures. The non-Gaussian fluctuations appear between the Berezinskii-Kosterlitz-Thouless transition temperature T-BKT and the mean-field transition temperature T-C. Subsequent theoretical analysis reveals that non-Gaussianity arises predominantly due to the percolative transition of a Josephson coupled network of superconductors. Our results confirm that the superconductivity in this system is confined to two dimensions. Our study of the non-Gaussian resistance fluctuation spectrum provides a novel means to explore the BKT transition in two-dimensional inhomogeneous superconductors.

It has been observed that, compared to bulk form, the nanocrystalline α-Fe2O3 is finding application in various areas. Magnetic properties of α-Fe2O3 are found to be influenced by the size of particles and are also sensitive to synthesis method employed for sample preparation. In the present work we have prepared a series of Nd doped α-Fe2−xO3 samples (x = 0.0–0.5) by combustion method, without using any fuel. The analysis of room temperature neutron diffraction patterns shows that all the compounds of the series form in the hematite (α-Fe2O3) structure, space group R−3c. Magnetization measurements show that there is a broad distribution of particle size in the samples. We find that the increase in the Nd content results in the dilution of magnetism of α-Fe2O3. From results we believe that inclusion of Nd in α-Fe2O3 drastically modifies the magnetic properties.

The effect of irradiation by 50 MeV Li3+ and 200 MeV Ag15+ ions on single crystals of Tl2Ca2Ba2Cu3O10 (Tl2223) superconductor has been investigated at different fluences. Isothermal magnetization hysteresis loops have been recorded at different temperatures using a SQUID magnetometer and the effect of irradiation on the critical current density, irreversible field, second magnetization peak and pinning force has been studied. Irradiation by 200 MeV Ag15+ ions resulted in increased hysteresis and irreversibility field while no change in second magnetization peak position and critical temperature was observed. A broadening in the hysteresis loop before the second magnetization peak was also observed for the crystals irradiated by Li3+ ions. Annealing of irradiated crystals at 500 °C resulted in reduction of point defects created by Li3+ ions.

We report a colossal resistance drop around insulator–metal transition temperature ( T MI ) in Sm 0.55 Sr 0.45 MnO 3 induced by direct current. Polycrystalline samples of Sm 0.55 Sr 0.45 MnO 3 were synthesized through solid state reaction method. They have been investigated by X-ray diffraction for phase evaluation, scanning electron microscopy for grain morphology and dc resistivity measurement techniques for resistivity–temperature behavior. The resistivity–temperature behavior has been measured with different biasing currents (1 mA, 2.5 mA, 5 mA, 10 mA and 50 mA). With increasing biasing current, the resistivity of the samples decreased drastically. The change in the resistivity of the samples for bias currents 1 mA and 50 mA at T MI was found to be ∼2560%. This phenomenon of electroresistance is discussed in view of strong interaction between carrier spins and localized spins in Mn ions and percolative mechanism of phase-separation.

We investigate the effect of ionic size variation on the electrical and thermodynamic properties in a series of Pr0.7Ca0.3−xSrxMnO3 (PCSMO) samples. The increase in Sr content results in an increase of the unit cell volume, as a bigger Sr2+ ion replaces the smaller Ca2+ ions. Resistivity measurements show that the increase in the Sr content also results in the induction of a metal–insulator transition (TMI), which increases with increasing Sr content. The activation energy (Ea), calculated from the resistivity data, decreases with increasing Sr content confirming the metallic character. The effect of the magnetic field on resistivity and specific heat has also been studied.

In this report, magnetization and magnetoresistance properties of pulse (PC) and direct current (DC) deposited Cu–Co alloy films containing 37 at.% of cobalt and higher were investigated. Magnetization measurements revealed, even at high cobalt content, the co-existence of superparamagnetic (SPM) nano-granules along with FM regions. Addition of saccharine within the electrolyte led to a reduction in the coercivity of the films but annealed samples had opposite effect on it. Room temperature magnetoresistance (MR) measurements showed resistance change due to anisotropic magnetoresistance (AMR) of the as-deposited films. Upon annealing, several times increase of MR was noticed with the appearance of typical giant magnetoresistance (GMR) behavior. A maximum negative GMR of 3.2% was obtained for annealed pulse plated Cu 62.5 Co 37.5 alloy film. For DC plated samples, addition of saccharine had noticeable effect on GMR compared to PC plated alloys.

In this paper, we report the control of important hysteresis parameters, which are useful for memory devices, viz. Ms, Hc and Mr/Ms, by changing the particle size/calcination temperature. An investigation of SrFe12O19 nanopowder from the structural and magnetic aspect is performed using X-ray diffraction (XRD), High Resolution Transmission Electron Microscopy (HRTEM), Scanning Electron Microscopy (SEM) and Vibrating Sample Magnetometer (VSM). The average particle size (APS) of SrFe12O19(nanopowder) increases from 26 to 600 nm with calcination temperatures of 400 and 1100 °C in air, respectively. With the increase in calcination temperature, saturation magnetization (Ms) increases with the decrease in coercivity for the respective sample. The change in saturation magnetization and coercive field are explained on the basis of transition from single domain structure to multi-domain geometry with an increase in the heating temperature. The sample heated at 1000 °C shows a minimum coercive field (2.71 kOe) and an appropriate squareness ratio (Mr/Ms) compared to other calcined samples.

We have studied the effect of chemical pressure on the magnetic properties of a series of Pr 0.7 Ca 0.3− x Sr x MnO 3 ( x = 0.0–0.3) (PCSMO) compounds. The parent compound Pr 0.7 Ca 0.3 MnO 3 (PCMO) is a well known charge-ordered compound. The selective substitution of Sr for Ca in PCMO leads to increase in electron count as a 4s metal (Ca) is being replaced by a 5s (Sr) alkali metal, resulting in melting of CO-state (in PCSMO) and increase in magnetic transition temperature ( T o ) from 85 K (for x = 0.0) to 260 K (for x = 0.3). The lattice distortion factors, such as A -site variance ( σ 2 ) and tolerance factor ( T f ) vary linearly with T o . The magnetocaloric effect (MCE shown as, Δ S ) calculated from isothermal magnetization measurement exhibits maximum (at T = T o ) for x = 0.2 for a field change from 0 to 50 kOe. The variation of Δ S ( x ) mimic the variation of Δ S ( σ 2 ), indicating the strong influence of Mn–O–Mn bond angle on the MCE. We discuss these results in terms of modification of magnetic properties in PCSMO through chemical pressure.

Comparative study on various systems originated from MSr 2 RECu 2 O z (M-1212; 0≤δ

We report the study on the effect of Pr doping on the structural and electrical properties of La0.9−xPrxSn0.1MnO3 (0 ≤ x ≤ 0.2) manganites. The X-ray diffraction (XRD) patterns for all the samples studied have been analyzed by Rietveld refinement method. The compounds are mixed phase with majority ABO3 (La1−xPrxMnO3) and minority La2Sn2O7 phases. The insulator–metal (I–M) transition temperature (TIM ∼ 237 K) of the pristine La0.9Sn0.1MnO3 sample shifts towards low temperatures and the resistivity increases with Pr doping. While the electrical conduction above TIM is dominated by the small polaron hopping, the metallic region below TIM is found to obey the electron–magnon scattering mechanism. With Pr doping, the conduction in metallic region shows a crossover from electron–magnon to electron–electron scattering. The re-entrant metal–insulator behaviour at low temperatures has been viewed in terms of the disordered metallic material and antiferromagnetic nature of PrMnO3. In conclusion the mixed multiphase system provided interesting structural and conduction mechanisms, being clubbed with each other.

In the present work, mixed magnesium–manganese ferrites of composition Mg0.9Mn0.1Al0.3CozFe1.7−zO4 where z=0.3, 0.5 and 0.7 have been synthesized by the citrate precursor technique. X-ray diffraction patterns of the samples confirmed the formation of single-phase spinel structure. The ferrites have been investigated for their electric and magnetic properties such as dc resistivity, Curie temperature, saturation magnetization, initial permeability and relative loss factor (RLF). Fairly constant value of initial permeability over a wide frequency range (0.1–20 MHz) and low values of the relative loss factor of the order of 10−4–10−5, in the frequency range 0.1–30 MHz, are the cardinal achievements of the present investigation. In addition to this, initial permeability was found to increase with an increase in temperature while RLF was observed to be low at these temperatures. The dc resistivity and Curie temperature were found to increase with an increase in cobalt content. The mechanisms contributing to these results are discussed in detail in this paper.

We have prepared a series of La2CaBa2Cu5O z (La2125) compounds by the standard solid-state reaction method. The oxygen stoichiometry in this R-123 type compound has been homogenized by two different methods. The first method is heating the sample in flowing oxygen at 500 °C for 6 hours and then slowly cooling to room temperature. The second method is to provide internal oxygen while sintering the sample by adding HgO or AgO. The addition of HgO or AgO in preparing oxide superconductors is advantageous when preparing them in bulk quantities, as HgO or AgO provide internal oxygen which is a much essential ingredient of the structure of oxide superconductors. Such a method of synthesis eliminates the need of additional oxygen annealing, thus enabling the synthesis in huge quantities at once. The composites referred to as La2125+xHgO and La2125+xAgO respectively, have been characterized by XRD, SEM, resistivity and magnetic measurements for their structural and superconducting properties. We compare the properties of oxygen-annealed and HgO/AgO added compounds and discuss the results in the light of applicability of such method in synthesizing bulk quantities of high-T c oxide superconductors.

We synthesized charge ordered La0.5Ca0.5MnO3 manganites by conventional solid-state route, which crystallizes in single-phase form having orthorhombic structure with Pbnm space group. The electrical transport of the compound exhibits highly semi-conducting behaviour from 300 K down to 130 K and showed an insulator–metal transition (TMI) with a sharp peak in ρ(T). The low temperature resistance below 30 K exhibits some upturn in the ρ(T). The charge ordered state (CO) of the Mn3+/Mn4+ ions is not clearly seen as a step in ρ(T), but the same could be seen as a change in the slope of M(T) curve around charge ordered temperature(TCO). Interestingly, when the sample is cycled for the resistance (R) measurements during cooling/heating process hysteresis of 12 K is seen near TMI. The magneto-transport of the synthesized compound in 7 T field, exhibits nearly 100% magnetoresistance (MR) between TMI and TCO. The fixed temperature (400, 300, 200, 130, 100 and 5 K) MR in ±7 T field exhibited up and down cusps at all the studied temperatures. The electrical transport, large hysteresis in ρ(T) and MR results can be explained in terms of complex phase separated magnetic structure of this compound around TMI.

We report the structural, optical, and magnetic properties of polycrystalline FeVO3 synthesized by solid state reaction technique.While FeVO3 has rhombohedral crystal structure with space group R-3c (167) identical to the parentα-Fe2O3, the lattice volume reduces due to the replacement of Fe3+ with V3+ having smaller ionic radii. The most remarkable outcome of doping is reduction in band gap from 2.1 (α-Fe2O3) to 1.5 eV (FeVO3), which is favorable for photo-electrochemical applications. Although the canted ferromagnetism persists in FeVO3, an enhancement in magnetic moment is observed as compared to the parent compound.

A fiber optic based probe is designed and developed for electrical transport measurements in presence of quasi-monochromatic (360–800 nm) light, varying temperature (T = 1.8–300 K), and magnetic field (B = 0–7 T). The probe is tested for the resistivity and Hall measurements performed on a LaAlO3–SrTiO3 heterointerface system with a conducting two dimensional electron gas.

We have studied resistance fluctuations in two different types of two-dimensional superconductors near to the Bcrczinskii-Kostcrlitz-Thoulcss (BKT) transition. The power spectral density of the resistance fluctuations was seen to deviate from 1/f as transition temperature is approached. We find that the shape of the spectrum can not be explained by a model for local defect fluctuations. Probability distribution function(PDF) and voltage-voltage auto-correlation functions provides evidence of the non-Gaussian nature of the resistance fluctuations near the BKT transition.

Despite continuous efforts, a conceptual perception on the origin of quasi-two-dimensional electron gas (q-2DEG) in oxide heterostructures remains far from any generalization. Along this perspective, a systematic study identifying systems that exhibit heterointerface conductivity (${\mathrm{LaAlO}}_{3}{/\mathrm{SrTiO}}_{3}$) and that do not (${\mathrm{LaCrO}}_{3}{/\mathrm{SrTiO}}_{3}$) is undertaken. High quality ${\mathrm{LaAl}}_{1\ensuremath{-}x}{\mathrm{Cr}}_{x}{\mathrm{O}}_{3}$ ($0\ensuremath{\le}x\ensuremath{\le}1$) films were fabricated on ${\mathrm{TiO}}_{2}$ terminated ${\mathrm{SrTiO}}_{3}$ (001) substrates using a pulsed laser deposition technique and its growth was monitored by reflection high energy electron diffraction (RHEED). The transport and photoemission spectroscopy experiments reveal that the the origin of heterointerface q-2DEG is associated with ${\mathrm{Ti}}^{3+}$ states and that it ceases to exist with increasing Cr ion concentration in the overlayer films. Following experimental evidences of the Cr concentration dependent metal-insulator electronic phase transition at the heterointerface, explanation is sought within the realms of a polar catastrophe model. Based on our transport and spectroscopy measurements, we propose that an electronic reconstruction drives the formation of q-2DEG for pristine LAO/STO and Al rich samples due to the formation of ${\mathrm{Ti}}^{3+}{/\mathrm{Ti}}^{4+}$ mixed valent state, while for heavily doped Cr samples, the required electron count necessary to solve the polar catastrophe instability are trapped in the ${\mathrm{LaAl}}_{1\ensuremath{-}x}{\mathrm{Cr}}_{x}{\mathrm{O}}_{3}$ overlayers in the Cr $3d$ states. These trapped electrons in the overlayers are manifested in the form of ${\mathrm{Cr}}^{2+}$ ions.

100 MeV Si+7 irradiation induced modifications in the structural and magnetic properties of Mg0.95Mn0.05Fe2O4 nanoparticles have been studied by using X-ray diffraction, Mossbauer spectroscopy and a SQUID magnetometer. The X-ray diffraction patterns indicate the presence of single-phase cubic spinel structure of the samples. The particle size was estimated from the broadened (311) X-ray diffraction peak using the well-known Scherrer equation. The milling process reduced the average particle size to the nanometer range. After irradiation a slight increase in the particle size was observed. With the room temperature Mossbauer spectroscopy, superparamagnetic relaxation effects were observed in the pristine as well as in the irradiated samples. No appreciable changes were observed in the room temperature Mossbauer spectra after ion irradiation. Mossbauer spectroscopy performed on a 12 h milled pristine sample (6 nm) confirmed the transition to a magnetically ordered state for temperatures less than 140 K. All the samples showed well-defined magnetic ordering at 5 K, whereas, at room temperature they were in a superparamagnetic state. From the magnetization studies performed on the irradiated samples, it was concluded that the saturation magnetization was enhanced. This was explained on the basis of SHI irradiation induced modifications in surface states of the nanoparticles.

We present the studies on the swift heavy ions (SHI) irradiation induced modifications in structural and magnetic properties of NiMn0.05TixMgxFe1.95 − 2xO4 for x=0.0 and 0.2 thin films grown by rf magnetron sputtering. We also present the effect of irradiation on the oxygen content of the thin films. X-ray diffraction (XRD) patterns of the as-deposited films reveal the spinel structure of the films. These ferrite films were irradiated with 190 MeV Ag ion for fluence range from 5 × 1010 to 1 × 1012 ions/cm2. The XRD pattern of the irradiated films shows strain-induced texture effect i.e. the spinel peaks get textured along (1 1 1) plane, whereas the (3 1 1) peak, which was the major peak with maximum intensity in the spinel ferrite, vanishes after irradiation. The XRD peaks in case of irradiated NiMn0.05Fe1.95O4 film were of very low intensity; however, the peak intensities of irradiated NiMn0.05Ti0.2Mg0.2Fe1.55O4 film were of high intensity up to 1 × 1011 ions/cm2 as compared to the pristine film. From the DC magnetization measurements, it has been observed that the saturation magnetization (Ms) decreases for NiMn0.05Fe1.95O4, whereas it increases for NiMn0.05 Ti0.2Mg0.2Fe1.55O4 thin film with ion fluence. The maximum Ms was observed for NiMn0.05Ti0.2Mg0.2Fe1.55O4 thin film irradiated with 1 × 1011 ions/cm2 and with further increase in ion fluence the magnetization decreased. The enhancement in the saturation magnetization of irradiated films may be due to the ion induced texturing of the films along (1 1 1) plane (an easy axis of spinel ferrite). Variation in the oxygen content on irradiation can affect the interatomic distance that can lead to change in the magnetic interaction. Therefore, to measure the oxygen content in the thin film on irradiation, Elastic recoil detection analysis (ERDA) studies have been performed. From the ERDA results, it is evident that the oxygen content in the samples remains same even up to the fluence value 1.52 × 1013 ions/cm2.

The present work is carried out to investigate the effect of co-substitution of non-magnetic ions, Mg+2 and Ti+4, at Fe site in a basic nickel ferrite. The single-phase formation of the materials was confirmed by XRD analysis. The effective modifications in the exchange interactions were observed from structural, magnetic and Mossbauer studies. The substitution of the two ions, Mg2+ and Ti4+, at Fe site reduces the saturation magnetization, Neel temperature (TN) and initial permeability (μi) with increasing concentration of substituents. The observed variations in different properties were discussed on the basis of the site occupancy of the metal ions in the crystal structures. 57 Fe Mossbauer studies reveal the reduction in magnetic moment on substitution. The relaxation is observed for the higher substitution level (x≥0.4) evident from the Mossbauer studies. The doublet along with the two sextet is observed in the Mossbauer spectra which is found to increase with the increased level of substituents and explained on the basis of domain wall oscillation and displacement model.

A series of samples of NiMn 0.05 Ti x Mg x Fe 1.95−2 x O 4 for x =0.0, 0.2 were prepared by conventional solid state technique. The spinel cubic structure of this ferrite was confirmed by powder X-ray diffraction technique. The samples were irradiated with 190 MeV Ag ion with different doses ranging from 1 × 10 11 to 1 × 10 13 ions/cm 2 . The Mossbauer studies were performed on unirradiated as well as irradiated samples. The Mossbauer study for unirradiated samples show a decrease in hyperfine field on the substitution of non-magnetic ions such as Ti 2+ and Mg 2+ at Fe site. On irradiation, no appreciable changes are observed in the Mossbauer parameters. However, the extent of the paramagnetic doublet area increased and the broadening of the sextet peaks with fluence clearly indicates the amorphization of the samples due to SHI irradiation. Also an increase in the quadruple splitting values at higher doses is being observed.

Swift heavy ion induced modifications on dielectric properties of NiMn 0.05 Ti x (Zn 2+ , Mg 2+ ) x Fe 1.95−2 x O 4 for x =0.0, 0.2 thin films were studied. Thin films of NiMn 0.05 Ti x (Zn 2+ , Mg 2+ ) x Fe 1.95−2 x O 4 for x =0.0, 0.2 were grown on Si substrate using RF magnetron sputtering. The films were irradiated with 190 MeV Ag ion for three different fluence values 5 × 10 10 , 5 × 10 11 and 1 × 10 12 ions/cm 2 . The dielectric constant, e , and dielectric loss, tan δ , as a function of frequency from 1 kHz to 1 MHz were measured at room temperature for unirradiated and irradiated thin films. The e for NiMn 0.05 Fe 1.95 O 4 and NiMn 0.05 Ti 0.2 Mg 0.2 Fe 1.55 O 4 of unirradiated and irradiated film decreases with frequency, which is explained by Koops’ model. The dielectric constant at high frequency decreases with increase in ion irradiation fluence values. The irradiated NiMn 0.05 Ti 0.2 Zn 0.2 Fe 1.55 O 4 films show an anomalous behavior. The dielectric constant below 20 kHz increases with irradiation as compared to pristine film, whereas above 20 kHz the dielectric constant for irradiated samples were less than the pristine samples but it increases with irradiation. Further the dielectric loss show an increase with the irradiation. All the irradiated films show a resonance peak, which was not present in the pristine films. Also with the increase in the dose the resonance peak was found to be shifted to the lower frequency.

The 50 MeV Li3+ ion irradiation induced modifications on structural and electrical behaviors of Mg0.9Mn0.1AlxFe2−xO4 ferrites have been studied. A compressive strain is generated by the ion irradiation, observed by the X-ray diffraction studies, which have modified the electrical properties of these materials. The dispersion of dielectric constant € ′ in Mg0.9Mn0.1AlxFe2−xO4 ferrites of unirradiated samples is attributed to Maxwell–Wagner type interfacial polarization and Koop’s theory. The dielectric constant of irradiated samples is decreased in magnitude from that of the unirradiated samples. This is explained on the basis of space charge polarization and the collective contributions of p- and n-type carriers. The electric loss parameter for irradiated sample shows the resonance peak, which can also be explained using Maxwell–Wagner interfacial polarization (matching of hopping frequency with frequency of an applied electric field). The resonance peaks in the unirradiated samples could not be observed as they probably lie beyond the measurable frequency range used in this work.

The swift heavy ion-irradiated nickel manganese ferrite system has been studied with the Mossbauer technique. The NiMn 0.05 Fe 1.95 O 4 system was synthesized using a solid state reaction technique. To ensure the single-phase spinel structure of the system powder X-ray diffraction has been performed. The powdered samples were irradiated with a 190 MeV Ag ion beam at various fluences in the range of 1×10 11 – 1×10 13 ions/cm 2 . Mossbauer studies have been performed on pristine and irradiated samples. The spectra obtained were resolved into two sextets and a paramagnetic doublet for all the samples using the NORMOS program. From the observation of the results obtained we can say that the increase in the paramagnetic doublet with the irradiation is due to ion-induced disorder.

Effect of swift heavy ion irradiation on the modifications in structural and superconducting properties of La-based mixed oxide thin film superconductors with stoichiometric composition La2−xDyxCayBa2Cu4+yOz (y=2x; x=0.3 and 0.5) have been investigated using 200 MeV Ag+15 ion irradiation. Superconducting thin films of x=0.3 and 0.5 samples synthesized using pulsed laser deposition technique on LaAlO3 substrate were irradiated with 200 MeV Ag ions. Elastic recoil detection analysis (ERDA) studies were performed on the thin films using 15 UD Pelletron facility at NSC, New Delhi, for the determination of the changes in oxygen content. Recoiled Ca, Cu and O atoms were detected using a large-area position sensitive ΔE–E detector telescope to understand the stoichiometric changes with the increase in irradiation dose. From the analysis of ERDA data, it is concluded that the oxygen content of the thin films remains constant and no stoichiometric changes are observed with increasing Ag ion irradiation dose ∼10 12 ions / cm 2 .