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Bi1.1-xPrxFeO3 (x = 0.00, 0.10, 0.15 and 0.20) samples were synthesized and their structural study was carried out using X-ray diffraction which manifests structural phase transformation for x > 0.15 from rhombohedral (R3c) to orthorhombic (Pnma) crystal symmetry, which is further confirmed by micro-Raman spectroscopy. The stiffening of phonon modes with increasing Pr-doping fraction has been attributed to the development of local stress in the lattice, reduction in bond length in the framework of the bond-order-length-strength correlation mechanism. Electronic structure studies carried out using soft x-ray absorption spectroscopy shows that O 2p orbitals exhibit enhanced hybridization with neighboring atoms. Moreover, the +3 valence states of Fe and Pr are also confirmed using Fe L-edge and Pr M-edge spectra and found to agree with Raman studies. These investigations provide evidence of the correlation between the bond--length and hybridization on such structural phase transformation in multiferroic materials.

We report the results of the studies on crystal structure, electronic structure and dielectric properties of Er1-xLaxFeO3 (ELFO) (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) orthoferrites synthesized by co-precipitation method. Rietveld refinement of the XRD data confirms the orthorhombic crystal structure for all the samples. The study of Fe L3,2 -edge X-ray Absorption spectroscopy shows the presence of Fe-ions in 3 + valence state in all the samples. Investigations on the dielectric behavior of ELFO samples over the wide frequency range of 20 Hz to 5 MHz show the increment in the dielectric constant with La-doping. ErFeO3 has the lowest value of dielectric constant whereas LaFeO3 has the highest value of dielectric constant among all the samples. Effect of grain and grain boundary contribution on the dielectric behavior is studied using complex dielectric permittivity. The observed colossal dielectric behavior in LaFeO3 is attributed to the combined contribution from the intrinsic dielectric constant of the material and that due to the modification in the microstructure.

We report the effect of electronic excitations induced modifications in the ferroelectric polarization in BiFeO3 (BFO) multiferroic films grown on 0.2% Nb doped SrTiO3 (SNTO) substrates by pulsed laser deposition. The BFO/SNTO films were irradiated with 200 MeV Ag+15 ions with ion fluences of 5 × 1010 to 5 × 1012 ions/cm2 and characterized by using X–ray diffraction (XRD), atomic force microscopy (AFM), ferroelectric polarization and near-edge X-ray absorption fine structure (NEXAFS) measurements. The XRD and AFM results show the creation of structural defects and oxygen vacancies by ion irradiation. Such defects induced enhancement in structural strain and reduction in mobility of charge carriers leading to the improvement in ferroelectric behaviour in BFO films. In addition, the local electronic structures investigated using NEXAFS studies reveal the significant change in spectral features suggesting the role of Bi-O and Fe-O hybridizations that modifies the ferroelectric behaviour of BFO films. These results are used to understand the mechanism.

Effect of Zn doping on the structural and magnetic properties of NdMnO 3 has been investigated by neutron diffraction and dc magnetic susceptibility measurements. The partial replacement of Mn 3+ by Zn 2+ results in the decrease in T N . In the temperature dependent magnetization measurements, a broad hump and a sharp peak has been observed around ~ 50 K and 10 K respectively for both the samples. Thermal hysteresis in magnetization between cooling and heating runs indicate first-order phase transition. Magnetization measurements on NdMn 0.95 Zn 0.05 O 3 sample clearly show that, 5% Zn-doping in NdMnO 3 results in the suppression in magnetism which is evident from the weakening of Nd–Mn interaction below T N , and resulting in antiferromagnetic coupling of Mn 3+ ions along x-axis with Mn 3+ moments oriented parallel or antiparallel to the x-component of Nd 3+ moments.

The electronic structure of Pulsed Laser Deposited (PLD) ZnO, Zn0.95Fe0.05O (ZFO), Zn0.98Al0.02O (ZAO) and Zn0.93Fe0.05Al0.02O (ZFAO) films were investigated by Photoelectron spectroscopy and X-ray absorption spectroscopy. X-ray diffraction and ϕ-scan measurements show epitaxial c-directional growth of the films. Temperature dependent magnetization and M-H loop measurements show the presence of room temperature magnetic ordering in all the films. Fittings of Fe 2p XPS and Fe L3,2 −edge XAS of ZFO and ZFAO films show the presence of Fe, in both, Fe+2 and Fe+3 states in tetrahedral symmetry. Valence band spectra in resonance mode show resonance photon energy at 56 eV showing the presence of Fe2+ state (∼2 eV) near the Fermi level. A significant effect of Fe and Al doping on the spectral shape of O K-edge XAS was observed. Results of the Spectroscopic studies reveal that, ferromagnetism in the films is due to the contribution of oxygen deficiency which increases the number of charge carriers that take part in the exchange interaction. Al co-doping with Fe (in ZFAO) results in the enhancement of saturation magnetization by increase in the carrier-mediated ferromagnetic exchange interaction.

We report the results of the structural, transport and magnetotransport studies on polycrystalline La0.5Sr0.5Mn1−xRuxO3 (x = 0.0 and 0.05) manganite investigated using XRD and resistivity (with and without field) measurements. Rietveld refinement of XRD patterns confirms the single phasic tetragonal structure for both the samples crystalizing in I4/mcm space group (No. 140). Low-temperature resistivity and MR measurements with H = 0 T & 5 T field show thermal hysteresis which has been attributed to the first order phase transition. The increase in resistivity and decrease in metal – insulator transition temperature (TMI) with Ru – doping concentration in La0.5Sr0.5MnO3 (LSMO) has been understood in the context of superexchange interaction between Mn and Ru ions. The observed upturn in resistivity at low temperature under field has been explained using combined effect of electron – electron (e - e) interaction, Kondo-like spin-dependent scattering and electron – phonon interaction while the variation in resistivity at high temperature (T > Tp) has been explained using adiabatic small polaron hopping model.

We present the results of studies on the dielectric properties of polycrystalline Bi1-xCaxFeO3 (x = 0.05, 0.10, 0.20) (BCFO) multiferroics. Rietveld refined XRD patterns confirm the single phasic n...

We report the results of the studies on structural, microstructural and transport properties of nanostructured PrMnO3 (PMO) synthesized by acetate precursor based modified sol-gel route. Role of sintering temperature in the modifications in the physical properties of PMO samples has been studied. Structural analysis, using X-ray diffraction (XRD), reveals the single phasic nature of all the PMO samples, while analysis of TEM reveals the uniform sized distribution of nanoparticles, showing agglomeration effect in samples sintered at higher temperatures. SEM micrographs depict the increase in grain size with sharp boundaries in the samples sintered at higher temperatures. Sintering temperature and size dependent resistivity behavior under different applied electric fields has been understood in the context of grain size and boundary nature. PMO have also been studied for their electroresistance (ER) and electric pulse induced resistance (EPIR) change behavior which are highly useful features for spintronic based practical applications.

We have reported in this work the study of correlation between electrical transport and magnetic properties of La 0.5 Ca 0.5 Mn 0.98 Bi 0.02 O 3 polycrystalline sample prepared by solid state method. Structural analysis reveals that presently studied compound crystallizes in the orthorhombic structure with Pnma space group. Temperature dependence of magnetization indicates that our studied compound undergoes a paramagnetic–ferromagnetic transition at Curie temperature T C =237 K. Magnetotransport analysis was successfully carried out using percolation model in the temperature range 40–300 K for magnetic field values up to 14 T. Strong correlation between electrical and magnetic properties was observed along with the absence of charge ordering inside the structure of our sample.

In this communication, we report the results of the studies on electrical properties of cost-effective modified sol–gel-grown nanostructured Gd0.95Ca0.05MnO3 (GCMO) manganites sintered at different temperatures. Structural investigations, carried out using X-ray diffraction measurements, reveal the single-phasic nature of GCMO samples having orthorhombic unit cell structure. Frequency-dependent variation in AC conductivity (σ AC) has been discussed on the basis of correlated barrier hopping (CBH) mechanism for the GCMO samples sintered at lower temperatures. Sintering temperature-induced transition from CBH mechanism to Maxwell–Wagner relaxation processes has been discussed in detail. Size-induced modifications in the impedance response of the samples have been understood, in detail, using size effects and Cole–Cole plots.

Structural and magnetic properties of polycrystalline bulk Er1-xLaxFeO3 (x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0) samples prepared by co-precipitation technique have been investigated. Rietveld refined x-ray diffraction patterns confirm a single phase orthorhombic crystal structure of all the samples. Substitution of La at Er-site significantly modify the magnetic properties of parent ErFeO3. The temperature-dependent magnetization study reveals that, all the samples exhibit antiferromagnetic ordering throughout the temperature range studied. All the samples become fully antiferromagnetic ~81 K with the lowest value of net magnetization. Erbium moments order at ~4.1 K. ErFeO3 sample exhibits compensation temperature TCOMP at ~48 K and spin reorientation TSR phenomena in the temperature range of ~85–98 K. The highest value of coercivity with nearly saturated M−H loops is observed at 2 K indicating the existence of weak ferromagnetic order due to the magnetic interaction between the Er3+ and Fe3+-ions.

Effect of Ca – doping on electronic structure and ferroelectric properties have been studied on PLD grown Bi1-xCaxFeO3/SNTO (x = 0.05, 0.10, 0.20) films. The structural study confirms single crystalline (100) oriented epitaxial growth of the films. The observed improvement in the ferroelectric behavior with an increase in Ca – doping has been attributed to the strong hybridization between Fe3d–O2p and localization of Fe3deg and Bi6s-O2p orbitals understood using X-ray Absorption Spectroscopy measurements. Ferroelectric measurements performed on BCFO films show the finite value of intrinsic ferroelectric polarization, though the contributions from the non – ferroelectric components lead to unsaturated and leaky loop. The sub-bandgap transition observed in the absorption spectra indicates the presence of oxygen vacancy states which is one of the reasons for observed leakage in polarization measurements.

We report the results of the modifications in structural and dielectric behaviour of pulsed laser deposited NdMnO 3 manganite thin films grown on (1 0 0) single crystalline (LaAlO 3 ) 0.3 (Sr 2 AlTaO 6 ) 0.7 substrate irradiated with the 200 MeV Ag +15 ion irradiation having different fluences, ∼5 × 10 10 , ∼5 × 10 11 , ∼5 × 10 12 ions/cm 2 . Structural strain was quantified using analysis of X-ray Diffraction data while Rutherford Backscattering measurements were performed on pristine NdMnO 3 film to confirm the elemental composition, thickness and oxygen content. Dielectric measurements performed on all the irradiated films show that, the dielectric constant decreases with increase in ion fluence which has been correlated with the irradiation induced increase in strain at the film-substrate interface. The dielectric relaxation behaviour of pristine and irradiated NdMnO 3 films have been understood by fitting the dielectric data using the Cole–Cole plots.

In this communication, we report the results of the studies on the effect of non-magnetic Al 3+ -doping on structure and properties of La 0.7 Ca 0.3 Mn 1− x Al x O 3 (LCMAO) manganites synthesized by conventional solid state reaction (SSR) route. The Rietveld refinement of the X-ray diffraction (XRD) data confirms the single phasic nature of the samples without any detectable impurities. All the samples exhibit metal to insulator transition ( T P ) which decrease with increase in Al 3+ doping concentration while it increases with applied magnetic field. To understand the nature of charge transport in metallic and insulating regions of resistivity, various models and mechanisms have been used to fit the observed experimental data.

In the present communication, we report the results of the studies on structural and microstructural properties of sol–gel grown nanostructured La0.6Nd0.1Sr0.3MnO3 (LNSMO) manganites sintered and annealed at different temperatures (viz., 700, 800 and 900 °C). It is shown that resistivity, magnetoresistance (MR) and magnetic behavior are strongly dependent on structure and microstructure of the LNSMO samples. Suppression in resistivity, decrease in MR and enhancement in metal to insulator transition temperature (TP) have been discussed in detail on the basis of grain morphology and role of oxygen. Magnetism of LNSMO samples has been discussed on the basis of variation in ferromagnetic to paramagnetic transition temperature (TC), irreversibility, freezing temperature, thermal hysteresis, M–H loop area, coercive field and remnant magnetization with process temperature and annealing environment.

We report the modifications in the electronic structure of Rare Earth (RE) doped polycrystalline BiFeO 3 (Bi 0.9 RE 0.1 FeO 3 (RE= La, Pr, and Er)) synthesized using conventional solid state reaction method. Structural studies using XRD shows that all the samples possess rhombohedral symmetry. As compared to Er and Pr-doped BiFeO 3 , La-doping results in the improvement in P–E behavior. X-ray absorption studies at Fe L-edge shows the presence of mixed valence state of Fe ions in all the samples. Interestingly, O K-edge spectra of La-doped BiFeO 3 shows enhancement in the intensity of the feature ‘b’ assigned to the hybridization of Bi 6s and O 2p orbital.

In this communication, we report the results of the structural, magnetic and transport studies on monovalent doped La1−xNaxMnO3 mixed valent manganites synthesized by conventional ceramic route. Structural study using XRD and Rietveld refinements of raw data shows that all the samples are single phasic in nature without any detectable impurities within the measurement range. Magnetic study and Arrott plots confirm the second order ferromagnetic (FM)–paramagnetic (PM) phase transition observed for all the samples. Effect of monovalent substitution and ration of Mn3+ to Mn4+ ions on resistivity and metal to insulator transition temperature (TP) has been discussed in the context of tolerance factor, size variance, zener double exchange (ZDE) mechanism and Jahn–Teller (JT) disorder. Metallic nature of the samples has been discussed using ZDE polynomial fittings while low temperature transport has been explained by resistivity minima. Temperature and field dependent magnetoresistance (MR) studies reveal the spin polarization effect and intrinsic and extrinsic MR contributions observed in presently studied samples.

In this communication, we report the results of the studies on structural, microstructural, transport and magnetotransport behavior of L0.8-xPr0.2SrxMnO3 (LPSMO) (x=0.1, 0.2 and 0.3) manganite films grown on (100) single crystalline SrTiO3 (STO) substrate using low cost chemical solution deposition (CSD) method. Films with similar compositions were also grown using sophisticated pulsed laser deposition (PLD) technique and results of structural and transport studies obtained for CSD grown films were compared with PLD grown films. Structural studies show that all the CSD and PLD grown films possess single crystalline nature with compressive and tensile strain, respectively. Surface morphology, studied using atomic force microscope (AFM), reveals the island like grain morphology in CSD grown films while PLD grown films possess smooth film surfaces. Carrier density dependent transport properties of the films have been discussed in the context of zener double exchange (ZDE) mechanism. Lower resistivity and higher transition temperature (T-p) observed in CSD grown films as compared to PLD grown films have been discussed in the light of structural strain and surface morphology of the films. Various models and mechanisms have been employed to understand the charge transport in CSD and PLD grown films. Also, observation of low temperature resistivity minima behavior in all the CSD and PLD grown LPSMO films has been explained in the context of electron-electron scattering mechanism. (C) 2015 Elsevier B.V. All rights reserved.

We have reported in this work the effect of the partial substitution of lanthanum by samarium on the structural, electrical and magnetic properties of La 0.5 Ca 0.5 MnO 3 . The magnetic study indicated that substitution promotes charge ordering and weakens ferromagnetism. Below T C =123 K, the compound La 0.4 Sm 0.1 Ca 0.5 MnO 3 is a mixture of ferromagnetic and charge ordered antiferromagnetic domains. Between T C and T CO =215 K, the structure is paramagnetic with the presence of antiferromagnetic domains. The fractions of the coexisting magnetic phases are highly dependent on the applied magnetic field value. Resistivity measurements reveal the presence of an insulating-metal transition at T ρ =123 K. The equality between T C and T ρ indicates the presence of a correlation between magnetization and resistivity. For only 1 T applied field, we have reported a colossal value of magnetoresistance reaching 73% around T C . The origin of this high value is attributed to phase separation phenomenon.

We report the structural, magnetic and magnetotransport properties of polycrystalline La0.5Ca0.5Mn1−xBixO3 (x=0, 0.02 and 0.05). Refinement of X-ray powder diffraction patterns shows that all samples crystallize with orthorhombic Pnma space group. For x=0.02, the sample shows an increase of unit cell volume as well as Curie temperature TC with the destruction of charge ordering (CO) state existing in parent compound. With 5% bismuth at the B-site, unit cell volume and TC decrease with an enhancement of CO state. Bismuth doping induces a spin glass like state at low temperature with the presence of Griffiths phase above TC. Magnetoresistance (MR) measurements show typical negative colossal magnetoresistance (CMR) at low temperature.

We report, the studies on the electronic structure and valence band modifications in sol–gel grown Zn1−xCoxO (x = 0, 0.5 and 0.15) samples, obtained using X-ray photoelectron spectroscopy (XPS) measurements. Structural studies confirm the single phasic hexagonal wurtzite structure having space group P63mc. XPS measurements of Co 2p core level indicate that, Co-ions are in +2 state in ZnO. Using valence band spectroscopy (VBS) and resonant photoemission spectroscopy (RPES) measurements, modifications in the electronic structure of Co-doped ZnO have been understood in the context of increment in the occupation of Co-3d states with Co-content which extends the VB maxima edge.

BiFeO3 (BFO) multifunctional oxide exhibits fascinating multiferroic properties suitable for potential application in nanoscale electronic devices such as non-volatile random accesses memory (FeRAM), field effect transistors, capacitors, logic circuits, etc. In this communication, we report the results of studies on 200 MeV Ag+15 ion irradiation-induced modifications in the structural, microstructural, electrical (I–V, C–V and P–E) and magnetic properties of pulsed laser deposited nanostructured BFO films grown on conducting SrTi0.998O0.002TiO3 (SNTO) substrates. Role of nanoscale structural defects and oxygen vacancies in modifying the physical properties of BFO/SNTO has been discussed in this work.

Present study reports the device characteristics of epitaxially grown La0.6Pr0.2Sr0.2MnO3/SrNb0.002Ti0.998O3 manganite before and after swift heavy ion irradiation at various ion fluences. The modification in the structural, morphological and electrical transport properties of La0.6Pr0.2Sr0.2MnO3/SrNb0.002Ti0.998O3 have been explained based on defect formation and interface annealing effect. Various charge transport models are used to fit the I–V characteristics and the present study suggests that thermionic emission mechanism governs the transport in the pristine and irradiated devices. Irradiation induced variation in structural strain, crystallinity and surface roughness are responsible for the change in transport behavior in the devices.

PLD grown ZnO/La0.7Sr0.3MnO3/SrTi0.998Nb0.002O3 nanostructured heterostructure has been studied for its nanoelectronic properties at room temperature under zero applied field. XRD φ-scan reveals the epitaxial growth of La0.7Sr0.3MnO3 (LSMO) film, while the transport of 10-nm LSMO manganite layer can be tuned with applied electric field using various field effect configurations. 10-nm LSMO layer shows a large change in resistance with the application of voltage, i.e., exhibiting colossal electroresistance (CER) ~100% (negative) and large positive electroresistance (ER) ~2683% under 4.5 V at room temperature. The variation scenario in 10-nm LSMO transport has been discussed on the basis of electric-field-induced modifications in the charge carrier density and electronic states.

Studies on the ZnO/La 0.5 Pr 0.2 Sr 0.3 MnO 3 (LPSMO)/SrNb 0.002 Ti 0.998 O 3 (SNTO) heterostructure having varying thickness of p-type LPSMO (100 nm – LP1) and (200 nm – LP2) manganite are carried out. ZnO/LPSMO (n–p) and LPSMO/SNTO (p–n) junctions of both the heterostructures exhibit good rectifying behavior in a wide range of temperature and applied field. Forward and reverse bias characteristics of both the junctions of heterostructures show opposite behavior. The observation of negative magnetoresistance (MR) at 5 K and positive MR at 300 K, in both the heterostructures, has been explained in the context of interface region effects and filling of energy bands of LPSMO manganite. Further, at high temperature, the heterostructures exhibit large temperature (46%K −1 ) and field (40%T −1 ) sensitivities. Dependence of transport, magnetotransport, I – V and sensing properties of the heterostructures, on the temperature, field and film thicknesses have been discussed in this communication.

Effect of oxygen partial pressure on the structural, transport and magnetic properties of BiFeO3 (BFO) films grown on n-type conducting SrNb0.002Ti0.998O3(SNTO) substrates has been investigated. Variation in oxygen partial pressure, during pulsed laser deposition (PLD), results in the modifications in the physical properties of the films. Rutherford Backscattering (RBS) measurement shows that, BFO/SNTO films grown at 100 and 300 mT oxygen partial pressures, exhibit better polarization and magnetization. Tuning of electrical and magnetic properties with oxygen partial pressure has been discussed in the light of oxygen vacancies. Various charge transport mechanisms have been discussed to understand the leakage current mechanisms in BFO/SNTO films.

Owing to the higher magnetic transition temperature (TC), above RT and large magnetoresistance (MR) exhibited by La0.7Pb0.3MnO3 (LPMO) manganite, we have carried out the studies on the effect of 200 MeV Ag+15 ion irradiation on LPMO films. It is interesting to note that, the modifications in the surface grain morphology and roughness in higher thickness (>200 nm) LPMO films, due to irradiation, affects the transport and magnetotransport, in a prominent manner, which has been understood in the light of enhancement in the scattering of charge carriers. The results of the structural, microstructural, transport and magnetotransport properties of pristine and irradiated LPMO films (150–350 nm) have been discussed in this communication.

We report the modifications in the structural and dielectric properties of polycrystalline Bi1-xCaxFeO3 (BCFO) (x = 0.05, 0.10, 0.20) multiferroics understood in the context of grain and grain boundary contribution to the complex impedance and modulus behavior. It is seen that, in BCFO with increase in Ca-concentration, the insulating nature of both, grain and grain boundaries gets enhanced. Analysis of the Nyquist plots confirm the presence of non –Debye type relaxation in all the Ca-doped BCFO samples.

We present the results of structural and dielectric measurements on pure and Co-doped ZnO, Zn1−xCoxO (x = 0.2, 0.4, 0.6, 0.8) oxides synthesized using Co-precipitation method. The structural and dielectric properties of all the samples were investigated by X-ray diffraction (XRD) and impedance spectroscopy measurements, respectively. Rietveld refined XRD data, reveals the single phase Hexagonal Wurtzite structure with the Co2+ ions getting occupied at Zn2+ site in all the samples. The dielectric constant (e′), dielectric loss (tanδ) and ac conductivity were measured as a function of frequency and Co-doping concentration.

Structural and magnetic properties of pure and Cu doped NdMnO3 manganites have been investigated using room temperature neutron diffraction and temperature dependent magnetization measurements. The partial replacement of Mn3+ by Cu2+ results in the modification in the magnetic behavior of NdMnO3 at low temperature. Temperature dependent magnetization measurements show an onset of magnetic ordering at T ∼ 80 K in pure NdMnO3 and at T ∼ 77 K in NdMn0.95Cu0.05O3. Field dependent magnetization behaviour reveals metamagnetic behaviour for both the samples below 25 K, which becomes considerably weak in NdMn0.95Cu0.05O3 sample at T = 5 K.

In this communication, we report the results of the studies on the grain boundary (GB) effect on the structural, microstructural and transport properties of nanostructured PrMnO3 (PMO) manganites synthesized by acetate precursor based sol – gel method. As synthesized PMO samples were sintered at various temperatures to understand the role of sintering temperature in modifying the structure – property correlations in the context of GB effects. Structural analysis using X-ray diffraction studies reveal the single phasic nature of all the PMO samples while TEM analysis reveals uniform particle size distribution with agglomeration effect observed in samples sintered at higher temperatures. SEM micrographs depict the increase in grain size with sharp grain boundaries in the samples sintered at a higher temperature. Size-dependent resistivity behavior of the PMO samples have been understood in the light of grain size modification and GB effect.

We report the effect of BaTiO3 (BTO) addition in ZnO on the dielectric behaviour of ZnO-BaTiO3 composite in the form of (1-x)ZnO–(x)BTO (x=0.2,0.3,0.4,0.5). Modifications in the structural and microstructural properties of the composite under study have been attributed to the addition of ferroelectric BTO in the host insulating ZnO matrix. Improvement in the overall dielectric performance of ZnO-BTO composite has been observed due to the increase in the dielectric constant and suppression of the dielectric loss. Study of dielectric behaviour of ZnO-BTO composite show that increasing in BTO concentration in ZnO matrix results in the grain boundary modifications and enhancement in relaxor behaviour which has been understood on the basis of percolation phenomena, wherein, BTO modifies the dipole arrangements leading to higher dielectric constant.

Structural and magnetic properties of pure and Zn doped NdMnO3 manganites have been investigated using neutron diffraction and ac susceptibility measurements. The partial replacement of Mn3+ by Zn results in the modification in the magnetic behavior of NdMnO3 at low temperature. Temperature dependent ac susceptibility measurements show a broad hump like behavior around ∼ 60 K suggesting the presence of antiferromagnetic ordering. Temperature dependent ND studies on NdMn0.95Zn0.05O3 sample revealed the evolution of antiferromagnetic order around ∼ 75 K, evident from the emergence of (010) Bragg reflection. The intensities of (101) and (111) Bragg peaks in ND patterns increases below 75K which has been attributed to the presence of ferromagnetic (FM) component, getting enhanced at low temperature. Results of the temperature dependent ND and ac susceptibility measurements on NdMn0.95Zn0.05O3 have been discussed in detail.

We report the results of the structural, transport and magnetotransport studies on mono-valent doped La1-xNaxMnO3 (LNMO) (x = 0.05, 0.1 and 0.15) manganites. XRD measurement and Rietveld refinement on LNMO samples shows that, all the samples crystallize in distorted rhombohedral structure without any additional impurity peaks. The d.c. four probe resistivity measurements show that, the metal-insulator transition temperature (TP) exhibited by the Na doped manganites increases and resistivity decreases with increasing x. This behavior has been explained on the basis of size disorder effect, tolerance factor variation and structural modifications due to large size mono-valent Na-doping. In the metallic region, the resistivity data have been fitted to the zener double exchange (ZDE) polynomial law for all the three samples. Magnetoresistance (MR) studies show a decrease in low temperature (5K) MR while increase in room temperature MR with increase in Na-content in the LNMO manganites.

Thin films of La0.8-xPr0.2SrxMnO3 (LPSMO) (x = 0.1, 0.2, 0.3) manganite, synthesized using pulsed laser deposition (PLD) technique, were irradiated by 200MeV Ag+15 ions with an ion fluence of 5 × 1011 ions/cm2. Structural and microstructural characterizations have been carried out using XRD and AFM show single crystalline nature of the films having island like grain growth. The structural and grain morphology modifications due to irradiation has been observed. Temperature dependent resistivity measurements have been carried out for all the films before and after irradiation, which reveal a reduction in the resistivity and enhancement in insulator - metal (I-M) transition temperature (TP) with Sr content (x) resulting in improved transport (reduced resistivity and enhanced TP) in the films which can be attributed to the irradiation induced improved crystallinity and grain morphology. Temperature coefficient of resistance (TCR) improves on irradiation which is useful for practical applications.

Nanostructured polycrystalline La0.7Ca0.3MnO3 (LCMO) and Nd0.7Sr0.3MnO3 (NSMO) manganites have been successfully synthesized at various temperatures ranging between 700 and 1100 °C using Sol–Gel method. Crystalline nature and morphology of the samples have been studied using XRD (Rietveld analysis) and TEM measurements. SEM studies reveal nanostructured grain morphology of LCMO and NSMO samples. It is observed that, with increase in sintering temperature, crystallinity and grain morphology get improved resulting in better transport. A strong dependence of transport on size variance has been observed in the systems studied. The modified transport and better magnetotransport properties of the manganites have been observed due to the large surface to volume ratio (surface contribution) in the nanostructured manganites. The observation of large low temperature MR in both the manganite systems and the interplay between the intrinsic and extrinsic MR components has been explained in the light of spin polarized tunneling effect, grain morphology, grain boundary nature and size disorder effect.

We report the results of studies of rectifying behavior, positive magneoresistance (MR), the charge-transport mechanism and the effect of an electric field on a ZnO (n)/La0.5Pr0.2Sr0.3MnO3 (LPSMO) (p)/SrNb0.002Ti0.998O3 (SNTO) (n) heterostructure comprising two p–n junctions fabricated using the pulsed laser deposition technique. The heterostructure exhibits rectifying behavior over a wide temperature and field range having hysteresis in I–V behavior (forward bias) due to the tunneling of charge carriers. It is also observed that, depending on the nature of the electric field bias to n-type ZnO and SNTO, the junction resistance becomes modified, which has been explained on the basis of spin injection in the heterostructure. The observation of unconventional positive MR at room temperature has been justified on the basis of interface effects and the reduction in barrier height obtained using fitting of the I–V data by a thermionic emission model.

We report the effect of 200 MeV Ag 15+ ion irradiation with fluence of ∼5 × 10 11 ions/cm 2 on the structure and surface morphology of thin film devices of La 0.6 Pr 0.2 Sr 0.2 MnO 3 (named as LPSMO) (p)/SrNb 0.2 Ti 0.8 O 3 (named as SNTO) (n) manganite grown by Pulsed Laser Deposition (PLD) technique. The n-type manganite layers studied were of thickness 50, 100 and 200 nm. After ion irradiation, the structural studies revealed improved crystallinity in the LPSMO/SNTO devices with the thickness of 50 and 200 nm. But the 100 nm films showed the formation of regular tracks like feature in their surface morphology after irradiation. All the irradiated films show suppression of resistivity at all the temperatures but it was different rate in 100 nm LPSMO films which may be attributed to the formation of linear track like defects.

We report the results of studies on the rectifying behavior and tunneling conduction in ZnO(n)/La0.5Pr0.2Sr0.3MnO3(LPSMO)(p)/SrNb0.002Ti0.998O3 (SNTO)(n) thin film heterostructure comprising of two p–n junctions fabricated using the Pulsed Laser Deposition (PLD) technique. A structural study using XRD ϕ -scan depicts the single-crystalline nature and confirms the phase purity while the transport studies using I – V measurements at various temperatures and fields reveal the rectifying behavior. The temperature and field dependent variation in the saturation voltage ( V C ) indicates that, the heterostructure exhibits negative magnetoresistance (MR) at low temperatures and positive MR at room temperature (RT) which can be understood on the basis of the interface effect at the junction. I – V curves obtained at all temperatures and fields show noticeable hysteresis during the positive voltage sweeping which has been attributed to the presence of the various conduction phenomena through the junctions in the presently studied heterostructure.

Effect of A-site disorder in half-doped La 0.5 Ca 0.5 MnO 3 created by the substitution of Tb at La site is studied through temperature dependent neutron diffraction, resistivity, and magnetization on La 0.375 Tb 0.125 Ca 0.5 MnO 3 (LTC) to identify the evolution of phases as a function of temperature and magnetic field. Contrary to the parent system, the paramagnetic (PM) to ferromagnetic (FM) transition is found to be of first order but becomes observable only in fields above 1 T. Absence of this transition in zero and low fields along with the observation of a very intriguing and irreversible M – H curve at low temperature raises the question about the ground state of the system. It is identified from the specially designed measurement protocol that the ground state of the system becomes FM, contrary to the parent LCMO. However, this remains masked because of the hindrance to the transformation kinetics of the PM–FM first order transition in low fields. Significantly, though the thermal hysteresis of the first-order transition decreases with the measurement field, collapse of such a behavior to a critical point is not observed in LTC, unlike earlier observations in some other manganites.

We have carried out a comparative study of structural, microstructural and magnetic properties of the two sets of Co-doped ZnO samples synthesized using solid state reaction and sol–gel method. Rietveld refinement of the X-ray diffraction data reveals single phase hexagonal wurtzite structure for all the samples, while the tunnelling electron microscopy measurements show the presence of nano-phase in the sol–gel grown Co-doped ZnO samples. It is found that, the microstructure strongly depends on the synthesis method adopted. Samples with higher Co-concentration synthesized by SSR route exhibit antiferromagnetism while SG grown Co-doped ZnO samples exhibit weak ferromagnetic behaviour. Improved magnetic phase in the SG grown samples has been attributed to the grain morphology.

We report the effect of film thickness on transport and magnetotransport in La0.7Pb0.3MnO3 (LPMO) manganite films grown on single crystalline LaAlO3 substrate using chemical solution deposition (CSD) technique. AFM measurements show the island type grain growth responsible for the strain at the film–substrate interface, while structural studies using XRD shows the presence of thickness dependent compressive strain in the films which modifies the transport and magnetotransport in LPMO/LAO films. The observation of low temperature resistivity minima behavior in all the LPMO films has been explained in the context of electron–electron scattering mechanism. The ZFC–FC magnetization measurements show the glassy state behavior below Tmin.

Strain-induced modifications in the structure, electronic structure, electrical, and ferroelectric properties of the Bi0.90Ca0.10FeO3 (BCFO)/Nb-doped SrTiO3 (100) films have been systematically studied in light of variation in film thickness. X-ray diffraction and ɸ-scan measurements confirm the single phase, (100) oriented epitaxial growth of all films. Room temperature absorption spectra show the presence of asymmetric broad peak around ∼2.5 eV, which is indicative of the presence of defect states inside the bandgap and is attributed to the oxygen vacancies. Improvement in the bipolar resistive switching behavior with a decrement in oxygen vacancies and improvement in ferroelectric properties with increasing film thickness suggest the crucial role of oxygen vacancies and strain in modifying the electrical properties of the BCFO films. Improvement in the ferroelectric behavior is attributed to the increment in the Fe 3d-O 2p hybridization, localization of Fe 3deg/Bi 6s-O 2p orbitals, and reduction in the oxygen vacancies with an increase in the film thickness. Observed stable retention and large ON/OFF switching ratio in BCFO films make them a promising candidate for application in the non-volatile memory device.

The structural, transport, and magnetotransport properties of single-phase, homogeneous nanostructured La0.7Sr0.3MnO3 (LSMO) manganites synthesized by the coprecipitation route were investigated and the effect of sintering temperature on the microstructure of LSMO compounds was studied. A strong dependence of transport and magnetotransport behavior on the microstructure and nature of grain boundaries has been observed in the single-phase LSMO sintered at various temperatures. High-field magnetoresistance (HFMR) at room temperature is found to increase [13% (LS6) to 25% (LS9)] while low temperature (5 K) magnetoresistance decreases [75% (LS6) to 46% (LS9)] under 9 T field with increase in sintering temperature, which has been attributed to the spin-polarized tunneling and spin-dependent scattering of charge carriers.

Nine layered manganite based multilayer structure of La 0.5 Pr 0.2 Sr 0.3 MnO 3 (LPSMO) {5}/La 0.5 Pr 0.2 Ba 0.3 MnO 3 (LPBMO) {4} has been successfully fabricated on a LaAlO 3 (LAO) substrate to study its field and temperature sensing properties. For studying the magnetotransport properties of this multilayer, current perpendicular to plane (CPP) and current in plane (CIP) mode resistivity measurements have been carried out in various fields up to 8T. Large temperature coefficient of resistance (TCR) ∼3% and field coefficient of resistance (FCR) ∼−29% alongwith an appreciably large MR ∼60% has been observed at room temperature (RT). The observed large field and temperature sensitivity of multilayer grown has been explained by comparing the results of magnetotransport in CPP and CIP mode.

We report the results of the temperature-dependent neutron diffraction measurements on the nearly half-doped (La0.325Tb0.125)(Ca0.3Sr0.25)MnO3 manganite sample. The simultaneous doping of magnetic Tb3+ and divalent Sr2+ in the La0.7Ca0.3MnO3 system results into a large A-site size disorder. Rietveld refinement of neutron diffraction data reveal that the single phase sample crystallizes in a distorted orthorhombic structure. Increased 〈rA〉 value affects the transport behavior that results into an insulating-like behavior of the sample. Under application of 1 T field sample exhibit insulating-like behavior while insulator–metal transition (TIM) is exhibited under 5 and 8 T fields. Variable range hoping (VRH) mechanism of charge carriers is exhibited in the insulating region. Field cooled and zero field cooled magnetization measurement shows the Curie temperature (TC)~47 K. The refinement of the ND data collected at various temperatures below 300 K shows that there is no structural phase transition in the compound. Around 100 K, a magnetic peak appears at lower angle that can be ascribed to the presence of the A-type antiferromagnetic (AFM) phase. Two more peaks are observed around 50 K at lower angles that can be fitted in CE-type antiferromagnetic phase. Splitting of the peaks at lower temperatures is the signature of orbital ordering in the presently studied nearly half-doped manganite system. Results of the detailed structural analysis of the temperature-dependent ND measurements on (LaTb)0.45(CaSr)0.55MnO3 sample has been discussed in the light of coexisting A-type and CE-type antiferromagnetic phases present in the sample at low temperature.