N. M. Murari

Structural, electrical, and magnetic properties of chemical solution deposited BiFe1−xTixO3 and BiFe0.9Ti0.05Co0.05O3 thin films

BiFeO3 (BFO), BiFe1−xTixO3, and BiFe0.9Ti0.05Co0.05O3 thin films were deposited on Pt/TiO2/SiO2/Si substrates by chemical solution deposition. BFO film has distorted rhombohedral R3c structure and in BiFe1−xTixO3 (104)/(110) reflections broadened suggesting limited grain growth with Ti substitution. The surface roughness (rms) decreased in the case of Ti substituted BFO. Up to 5% Ti in the lattice reduces the leakage current substantially. For BiFe1−xTixO3, the leakage current qualitatively followed the same trend and the behavior resembles to space charge limited current conduction. The magnetic properties were completely lost by Ti substitution and slightly recovered upon cosubstitution with magnetically active Co. The disappearance of ferromagnetic hysteresis of BFO with Ti substitution and its reappearance with Co is suggestive of the origin of magnetic properties consequential from the BFO lattice itself and hence support it as an intrinsic property of BFO. Capacitance-voltage characteristics of BFO,...

DyScO3 buffer layer for a performing metal-ferroelectric-insulator-semiconductor structure with multiferroic BiFeO3 thin film

Metal-ferroelectric-insulator-semiconductor structures with a BiFeO3 ferroelectric layer and DyScO3 insulating buffer layer were fabricated and characterized. BiFeO3 film was polycrystalline with rhombohedral structure and DyScO3 film was amorphous. The size of the capacitance-voltage memory window (ΔVFB) was investigated as a function of voltage sweep and frequency; ΔVFB increased to a saturation value of 1.7 V with the sweep voltage and it almost remained constant over a frequency range of 1 kHz to 1 MHz.

Structural, electrical, and magnetic properties of chemical solution deposited Bi(Fe0.95Cr0.05)O3 thin films on platinized silicon substrates

Polycrystalline BiFeO3 and Bi(Fe0.95Cr0.05)O3 thin films were deposited on Pt/TiO2/SiO2/Si substrates by chemical solution deposition. Their structural, electrical, and magnetic properties were measured and compared. The prominent splitting around 2θ∼32° for the 104/110 reflections and the resemblance of Raman spectra with BiFeO3 suggests structural invariance upon Cr substitution (≤5%). The surface morphology of the films showed uniform granular grains; roughness and the grain sizes reduced considerably with Cr substitution. In the case of Bi(Fe0.95Cr0.05)O3 thin films, all Raman active modes disappeared at 700 °C suggesting a structural phase transition with the reduced transition temperature compared to pure BFO. The dielectric constant of pure BiFeO3 film is approximately 50 at 1 MHz and it increased to 66 with 5% Cr substitution. The leakage current reduced in Bi(Fe0.95Cr0.05)O3 thin films and the current conduction was due to Poole–Frenkel mechanism compared to the space charge limited current condu...

Reduced leakage current in chemical solution deposited multiferroic BiFeO3∕Ba0.25Sr0.75TiO3 heterostructured thin films on platinized silicon substrates

Multilayered metal-insulator-metal structures with BiFeO3 and Ba0.25Sr0.75TiO3 thin films were fabricated by chemical solution deposition to reduce the leakage current through the capacitor stack. The Ba0.25Sr0.75TiO3 layer does not influence the crystalline structure of BiFeO3 and was recognized as rhombohedral by Raman studies. Compared to pure BiFeO3, in the heterostructures, the coercivity increased, but the saturation magnetization and the leakage current were reduced. The frequency and the temperature dependence of the dielectric properties of the heterostructured film showed evidence of space charge developed between the layers of different dielectric constant (Ba0.25Sr0.75TiO3-BiFeO3 interface).

Probing the ferroelectric phase transition through Raman spectroscopy in Pb (Fe2/3W1/3)1/2Ti1/2O3 thin films

The present work investigates the evolution of micro-Raman spectra of (1−x)Pb(Fe2∕3W1∕3)O3−xPbTiO3 (PFWT) (x=0.50) thin films in the temperature range from 80to600K. Raman and dielectric data indicate that the crystal structure changes from tetragonal to cubic, i.e., a ferroelectric phase transition at 575K. The dielectric properties of PFWT thin films were studied in the temperature range of 80–600K over a wide range of frequencies. The slope of the reciprocal of the dielectric constant is 2:1, matched well with the simplest Landau free energy model, and it indicates a continuous second order displacive ferroelectric phase transition.

Diffused phase transition and relaxor behavior in Pb(Fe2∕3W1∕3)O3 thin films

The authors have synthesized Pb(Fe2∕3W1∕3)O3 thin films on Pt∕Ti∕SiO2∕Si(100) substrates utilizing chemical solution deposition method. The dielectric relaxation was studied as a function of temperature (100–300K) and frequency (100Hz–1MHz). A broad range of dielectric maxima was found, which shifted towards higher temperature with increase in frequency. The relaxation indication coefficient (γ) and broadening parameter (Δ) were estimated from a linear fit of the modified Curie-Weiss law and were found to be 2.00 and 50K, respectively; indicating strong relaxor behavior. A remarkably good fit to Vogel-Fulcher relationship further supports the relaxor nature of the films. The slim hysteresis loop at low temperature is indicative of ferroelectricity due to the growth of nanopolar regions.

Observation of one magnon and magnon-phonon-electric dipole coupling in multiferroics bismuth ferrite thin films

We observed “one magnon,” scattering in multiferroic polycrystalline BiFeO3 thin films near 17.2cm−1 at 90K employing Raman spectroscopy. It is seen with a kink in magnon intensity at 150K and with strong anomaly near 210K illustrating spin reorientation transition. The spectral weight of one magnon transferred to the lowest phonon mode near the spin reorientation temperature suggests magnon-phonon coupling. Dielectric constant and dielectric loss as function of temperature showed anomaly at 210K suggesting magnon-phonon-electric dipole coupling. The one magnon becomes overdamped or overcome by elastic scattering at elevated temperatures.

Dielectric properties and electrical conduction of high-k LaGdO3 ceramics

The temperature and frequency dependent dielectric properties and leakage conduction mechanism in LaGdO3 (LGO) ceramics have been studied, and this material has been identified as a potential high-k candidate for the future complementary metal-oxide-semiconductor (CMOS) and dynamic random access memory (DRAM) technology nodes. The dielectric constant and the loss tangent at 100 kHz were ∼21.5 and ∼0.003, respectively, at ambient conditions without any significant temperature and voltage dependence. The ac conductivity shows the typical features of universal dynamic response (UDR) and obey the double power law σac=σdc+Aωn1+Bωn2 with three types of temperature dependent conduction processes involved; (i) a dc plateau (< 3 kHz) due to long range translational hopping, (ii) a mid frequency region due to the short range hopping (3–100 kHz), and (iii) a high frequency region due to localized or reorientational hopping (100–1000 kHz). The temperature dependent dc conductivity follows the Arrhenius relation with ...

Direct observation of fatigue in epitaxially grown Pb(Zr,Ti)O3 thin films using second harmonic piezoresponse force microscopy

Here, we present a direct observation of fatigue phenomena in epitaxially grown Pb(Zr0.2Ti0.8)O3 (PZT) thin films using second harmonic piezoresponse force microscopy (SH-PFM). We observed strong correlation between the SH-PFM amplitude and phase signals with the remnant piezoresponse at different switching cycles. The SH-PFM results indicate that the average fraction of switchable domains decreases globally and the phase delays of polarization switching differ locally. In addition, we found that the fatigue developed uniformly over the whole area without developing region-by-region suppression of switchable polarization as in polycrystalline PZT thin films.

Fabrication of BiFeO3 capacitor structures with reduced leakage current

Multi layered metal-insulator-metal (MIM) structures with BiFeO3 (BFO) and Ba0.25Sr0.75TiO3 (BST) thin films were fabricated by chemical solution deposition. Crystalline structure of BFO was recognized as rhombohedral and was not influenced by the BST intermediate layer. Compared to the homogenous BFO, in the heterostructures, coercivity increased and saturation magnetization reduced. BST intermediate layer between the substrate and BFO layer resulted in the leakage current reduction by 3 orders of magnitude. The frequency and temperature dependent dielectric properties showed space charge accumulation between the layer of BST and BFO, and hence Maxwell-Wagner type dispersion.