R. Palai

β phase and γ-β metal-insulator transition in multiferroic BiFeO3

We show that epitaxial (001) thin films of multiferroic bismuth ferrite BiFeO3 are monoclinic at room temperature instead of tetragonal or Rhombohedral as reported earlier . We report a orthorhombic order-disorder beta-phase between 820C and 950C contrary to the earlier report. The transition sequence monoclinic-orthorhombic phase in (001)BiFeO3 thin film (rhombohedral-orthorhombic transition in single crystal) resembles that of BaTiO3 or PbSc1/2Ta1/2O3. The transition to the cubic

Impedance spectroscopy analysis of Ba0.7Sr03TiO3/La0.7Sr0.3MnO3 heterostructure

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Observation of Spin-glass-like Behavior in SrRuO3 Epitaxial Thin Films

-phase causes an abrupt collapse of the bandgap toward zero (insulator-metal transition) at the orthorhombic-cubic beta-gamma transition around 950C. This transition is similar to the metal-insulator transition in Ba0.6K0.4BiO3.

Polarized Raman scattering in monolayer, bilayer, and suspended bilayer graphene

Impedance spectroscopy technique has been used to study the effect of grains and grain boundaries in a heterostructure constituted with ferromagnetic La0.7Sr0.3MnO3 (LSMO) and ferroelectric Ba0.7Sr0.3TiO3 (BST) layers grown by pulsed laser deposition technique on (1?0?0) oriented MgO substrate. Frequency and temperature dependence of the complex impedance and complex electric modulus were measured in (BST20u.c,/LSMO10u.c)25 over a temperature range of 360?500?K. Non-Debye relaxation was observed in the investigated system. An equivalent circuit and the modified constant phase element circuit were used to describe the impedance spectroscopy, and excellent agreement between the calculated and measured curves was obtained from each model. The activation energy (~0.25?eV?0.48?eV) has been obtained from Arrhenius fitting of different relaxation processes present in the material, and its characteristic values support a model of Maxwell?Wagner relaxation in the heterostructured film at elevated temperatures and in the low frequency range. The electrical ac and dc conductivity studies showed that the heterostructure possesses negative temperature coefficient of resistance properties. It was found that the resistance of grain boundaries was larger than the resistance of intra-grains.

Study of physical properties of integrated ferroelectric/ferromagnetic heterostructures

Integration of functional materials (oxides of ferroelectrics and multiferroics) into silicon technology is of great technological and scientific interest. The current interest in functional oxides is largely based on engineered epitaxial thin films because of their superior properties compared to the bulk and polycrystalline thin films and their technological applications in dynamic random access memories, magnetic recording, spintronics, and sensors [1, 2, 3]. Most of these applications require bottom and top electrodes to exploit the electronic properties of the functional materials. SrRuO3 (SRO) has been found to be very useful for electrodes and junctions in microelectronic devices because of its good electrical and thermal conductivity, better surface stability, and high resistance to chemical corrosion, which could minimize interface electrochemical reactions, charge injection in oxide, and other detrimental processes [4, 5] thus improving retention, fatigue re

Phase transition and magneto-electric coupling of BiFeO3–YMnO3 multiferroic nanoceramics

Polarized resonant Raman scattering studies have been performed on monolayer, bilayer, and suspended bilayer graphene. The intensity of the G band is found to be unchanged with polarization in monolayer and bilayer graphene, whereas it shows polarization dependence in suspended bilayer graphene. The 2D mode shows strong polarization depended behavior for all the samples, irrespective of layer thickness. It is found that the intensity of the 2D peak is at a maximum when the incident photon is parallel to the scattered photon and at a minimum when these are perpendicular to each other. This effect has been explained on the basis of anisotropic photon scattering through the nodes at the K-point of the Brillouin zone in graphene during optical absorption.

Electrical conductivity and photoresistance of atomic layer deposited Al-doped ZnO films

Superlattices (SLs) with different periodicity of ferromagnetic La0.7Sr0.3MnO3 (LSMO) and ferroelectric Ba0.7Sr0.3TiO3 as constitutive layers were fabricated on conducting LaNiO3 coated (001) oriented MgO substrates using pulsed laser deposition. The crystallinity, ferroelectric, and magnetic properties of the SLs were studied over a wide range of temperatures and frequencies. The structure exhibited ferromagnetic behavior at 300 K and ferroelectric behavior over a range of temperatures between 100 and 300 K. A frequency-dependent change in dielectric constant and tangent loss were observed above the ferromagnetic-paramagnetic temperature. The frequency-dependent dielectric anomalies are attributed to the change in metallic and magnetic nature of LSMO and also the interfacial effect of two different phases that are connected alternatively in series. The effect of ferromagnetic LSMO layers on ferroelectric properties of the SLs indicated strong influence of the interfaces. The asymmetric behavior of ferroe...

Phase transition and enhanced magneto-dielectric response in BiFeO3-DyMnO3 multiferroics

We report the crystal structure, dielectric, magnetic, and magneto-electric properties of (1−x) BiFeO3-xYMnO3 (0.00 ≤ x ≤ 0.2) multiferroic nanoceramics prepared by auto-combustion technique. YMnO3 substitution is found to induce a structural phase transition from R3c to R3c+Pbnm after x ≈ 0.1 using Rietveld refinement technique. Field emission scanning electron micrographs show decrease in grain size with increase in YMnO3 content. The dielectric permittivity and loss tangent are found to be increased with composition x. The anomalies noticed from the temperature dependent dielectric analysis reveal the signature of magneto-electric coupling in the system. A decrease in magnetic ordering temperature as a function of composition is found from dielectric study. At room temperature, the dielectric permittivity of all the YMnO3 modified samples decrease with increasing magnetic field. The maximum value of magneto-electric coupling coefficient (e(H)-e(0))/e(0) is found to be ∼ −5.5% at H = 2 T for x = 0.2. Th...

Observation of strong magnetoelectric effects in Ba0.7Sr0.3TiO3/La0.7Sr0.3MnO3 thin film heterostructures

Al-doped ZnO films were deposited by the atomic layer deposition (ALD) on both glass and sapphire (0001) substrates. The Al composition of the films was varied by controlling the Zn:Al pulse cycle ratios. The films were characterized by the atomic force microscopy, x-ray photoelectron spectroscopy, x-ray diffraction, and optical measurements. The Film resistivity was measured as a function of Zn:Al cycle ratios as well as temperature for films grown at various substrate temperature used for ALD deposition. The resistivity of the ALD grown films decreases significantly, and so as the increase in the carrier concentration as the cycle ratio increases. The systematic measurements of temperature dependence of resistivity of films at various cycle ratios clearly demonstrate the crossover of the metal–semiconductor–insulator phase with the function of temperature as well as the cycle ratios. The average transmission of all films is greater than 85% and the optical absorption increases significantly in the visib...

Fabrication and characterization of relaxor ferroelectric PbFe1/2Ta1/2O3 thin film: A comparison with ceramics

We report systematic studies on crystal structure and magneto-dielectric properties of (1 − x) BiFeO3-x DyMnO3 (0.0 ≤ x ≤ 0.2) nanoceramics synthesized by auto-combustion method. Rietveld refinement of X-ray diffraction data indicates a structural transition from R3c to R3c + Pn21a at x = 0.1. Field emission scanning electron micrographs display a decrease in grain size with increase in x. The presence of dielectric anomalies around antiferromagnetic transition temperature implies the magnetoelectric coupling. Dielectric measurements showed decrease in magnetic ordering temperature with increasing x in agreement with differential scanning calorimetry results. A significant increase in magnetization has been found with increasing DyMnO3 substitution. Magneto-impedance spectroscopy reveals a significant change (∼18%) in dielectric permittivity at H = 2 T for x = 0.2.