Savan Katba

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...

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.

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.

Grain morphology dependent dielectric behaviour of ZnO – BaTiO3 composites

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.

Modification in the dielectric behavior of cobalt doped ZnO synthesized by co-precipitation method

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.

Structure & magnetic behavior of Cu doped NdMnO3 manganite

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.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.

Grain boundary effects on the structural, microstructural and transport behavior of sol – gel grown PrMnO3 nanoparticles

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.

Impedance studies on Ca – doped BiFeO3 multiferroic: Role of grain and grain boundary

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 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.

Magnetic structure and magnetism of divalent Zn doped NdMnO3

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.

Resistive switching and magnetic behavior of Bi0.8Ba0.2FeO3 / SrRuO3 / SrTiO3 films: role of thickness-dependent strain

The thickness-dependent resistive switching and magnetic behavior of Bi0.8Ba0.2FeO3/SRO/STO (1 0 0) films have been studied in the context of strain modifications introduced by varying the film thickness. Generation of misfit dislocation results in strain relaxation with an increase in film thickness. All films (50, 100 and 200 nm) show hysteresis in I–V behavior at room temperature with applied voltage V max = ±5 V. Fitting of I–V data suggests that trap-controlled SCLC governs the conduction in HRS in the 50 nm film while in the 100 nm and 200 nm films, the charge transport mechanism is ohmic-type throughout the applied field. The ON/OFF switching ratio and current retention performance decrease with an increase in film thickness, suggesting that substrate-induced strain and interface modifications play an important role in governing the resistive switching mechanism in Bi0.8Ba0.2FeO3 films. A film with lower thickness ~50 nm is found to exhibit the highest magnetization which may be attributed to the increase in oxygen vacancies and compressive strain.