Megha Vagadia

Improvement in resistive switching of Ba-doped BiFeO3 films

We investigate the resistive switching behavior of Ba-doped BiFeO3 (BBFO) films grown on single crystalline SrTi0.99Nb0.01O3 substrates. Observation of diode like I-V behavior and reduction in VC with Ba-content in BBFO films have been understood in the context of modifications in its energy band diagram. Also, I-V curves exhibit hysteresis which has been explained on the basis of migration and recombination of oxygen vacancies under field conditions. Furthermore, increment in Ba-content improves the retention property and ON/OFF switching ratio in BFO films which makes them suitable for applications in switching devices.

Electroresistance and field effect studies on manganite based heterostructure

Electronic properties of manganites are significantly important for various spintronic applications such as microelectronics, magnetic data storage, communication technologies, and memory devices. Influence of applied electric field on the room temperature charge transport in ZnO/La0.7Sr0.3MnO3/SrNb0.002Ti0.998O3 (SNTO) heterostructure has been investigated using field effect studies. Large negative and positive electroresistance has been observed in heterostructure under various possible circuit geometries. Field effect studies have been carried out using three different circuit geometries, namely: (i) ZnO as a control electrode (ELZ), (ii) SNTO as a control electrode (ELS), and (iii) shorted ZnO and SNTO as control electrodes (ELZS). For this, channel electric field (ECH) dependent variation in channel resistance (RC) (of manganite channel) and I-V (across manganite channel) under various control fields (EC) have been studied. Variation in barrier height (ΦB) with control field (EC) for different geomet...

Role of defects in BiFeO3 multiferroic films and their local electronic structure by x-ray absorption spectroscopy

Present study reports the role of defects in the electrical transport in BiFeO3 (BFO) multiferroic films and its local electronic structure investigated by near-edge X-ray absorption fine structure. Defects created by high energy 200 MeV Ag+15 ion irradiation with a fluence of ∼5 × 1011 ions/cm2 results in the increase in structural strain and reduction in the mobility of charge carriers and enhancement in resistive (I-V) and polarization (P-E) switching behaviour. At higher fluence of ∼5 × 1012 ions/cm2, there is a release in the structural strain due to local annealing effect, resulting in an increase in the mobility of charge carriers, which are released from oxygen vacancies and hence suppression in resistive and polarization switching. Near-edge X-ray absorption fine structure studies at Fe L3, 2- and O K-edges show a significant change in the spectral features suggesting the modifications in the local electronic structure responsible for changes in the intrinsic magnetic moment and electrical transp...

Dielectric and Magnetic Behavior of Sol‐Gel Grown BiFeO3 Multiferroic

We report the dielectric and magnetic properties of BiFeO3 (BFO) multiferroic synthesized by modified sol‐gel route. Frequency dependent dielectric constant and loss studies show higher value at lower frequencies while temperature dependent dielectric behaviour show higher value of dielectric constant above 250 K. Low magnetization value is exhibited by the BFO sample studied. DTA study shows the phase transition at 340° C and 816° C.

Role of strain and nanoscale defects in modifying the multiferroicity in nanostructured BiFeO3 films

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.

Swift Heavy Ion Irradiation Studies on the Transport in La0.8-xPr0.2SrxMnO3 Manganite Films

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.

Electrical properties of BaTiO3 based – MFIS heterostructure: Role of semiconductor channel carrier concentration

Effect of semiconductor channel carrier concentration on the modifications in the electrical properties of Ag/BaTiO3/SrTiO3/ZnO Metal-Ferroelectric-Insulator-Semiconductor (MFIS) heterostructure has been investigated. Under 4 V applied voltage, low leakage current density ∼3.2 × 10−6 A/cm2, has been observed in ZnO based MFIS heterostructure, which becomes ∼5.0 × 10−6 A/cm2 for MFIS with Al:ZnO channel. Observation of counterclockwise butterfly shaped C-V behavior confirms that, hysteresis in C-V is due to spontaneous ferroelectric polarization and field effect. A device with ZnO semiconductor exhibit ∼2700% modulation which decreases to ∼800% for Al: ZnO channel with good retention behavior. Pulse induced write/erase repeatability of source/drain current confirms the usefulness of the presently studied devices for non-volatile switching memory application.

Studies on the dielectric behavior of Cu-doped NdMnO3

We report the effect of Cu-doping on the dielectric behavior of NdMn1−xCuxO3 (NMCO); x = 0.0 – 0.05, manganites. It is observed that, dielectric constant (e′) decreases with Cu (x) concentration which has been understood on the basis of modifications in grain morphology and double exchange (DE) interaction between Mn3+ and Mn4+. Also, effect of grain boundary (GB) density on the dielectric response is studied using cole-cole plots.

Dielectric behaviour of PLD grown BiFeO3 multiferroic thin films

We report the dielectric behaviour of BiFeO3 thin films deposited on Nb doped STO substrate using Pulsed Laser Deposition technique. Frequency dependent real and imaginary dielectric permittivity in the temperature range 20°C to 350°C show good dielectric behaviour exhibited by 100 and 200 nm films.

Studies on the structure and dielectric properties of Ca-doped BiFeO3 multiferroics

ABSTRACT 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 nature of 5% & 10% Ca – doped samples crystallizing in superimposed R3c (Rhombohedral) + Pm 3m (Cubic) space group symmetry while 20% Ca – doped sample crystallize in Pm 3m symmetry. Frequency and temperature dependent dielectric constant (ϵ) studies show the contribution of grain and grain boundaries in the system. Complex impedance graph exhibits a single semicircular arc for all the samples, indicating the contribution of grain interior (bulk) property of the material.