D.R. Sahu

Magnetic properties of La0.6Sr0.4MnO3 thin films on SrTiO3 and buffered Si substrates with varying thickness

La0.60Sr0.40MnO3 (LSMO) thin films of varying thickness from 12 to 55 nm were deposited using the pulsed-laser deposition technique onto single-crystalline SrTiO3 (STO) and STO-buffered Si substrates. The Tc of LSMO films grown on STO-buffered Si substrates decreases faster than films directly grown on STO with decreasing film thickness. The LSMO/STO film with thickness of 55 nm shows Tc at about 360 K, which is close to the bulk value, whereas Tc LSMO film on STO-buffered Si film of similar thickness is reduced to 320 K. This difference is attributed to the strain and interfacial disorders in LSMO film on STO/Si. The film surface morphology is influenced by the film thickness. Oxygenation of LSMO films on STO-buffered Si affects the Tc minimally but improved the overall magnetization of the films due to better oxygenation, which is also the case for postannealing the sample at elevated temperatures. The thermomagnetic history effects observed in LSMO films of STO-buffered Si indicate the presence of inho...

Studies on the properties of sputter-deposited Ag-doped ZnO films

Ag-doped ZnO films were prepared by simultaneous rf magnetron sputtering of ZnO and dc magnetron sputtering of Ag on glass substrate. The influences of dopant content and substrate temperature on the properties of the as-grown films were investigated. Several analytical tools such as X-ray diffraction, spectrophotometer, atomic force microscopy, scanning electron microscopy and four-point probe were used to explore the possible changes in electrical and optical properties. The as-grown film has a preferred orientation in the (002) direction. As the amounts of the Ag dopant were increased, the crystallinity as well as the transmittance and optical band gap were decreased while the electrical resistivity increased. However, as the substrate temperature was increased, the crystallinity and the transmittance were increased. A small amount of Ag (<1at%) lowered the resistivity by ~30% with only a slight decrease in the visible transparency.

Lanthanum-based manganite films on MgO using SrTiO3 as a template layer

We report on the processing and characterization of high performance epitaxial manganite films grown on SrTiO3 and SrTiO3 buffered MgO substrates with a Tc tailored to room temperature. We have demonstrated that La1−xBaxMnO3 and La1−xSrxMnO3 epitaxial films on SrTiO3 buffered MgO substrate show significantly improved transport and magnetization properties in the vicinity of room temperature on ex situ annealing at 900 °C. Our results suggest that manganite films can be grown on either SrTiO3 or SrTiO3 buffered MgO substrates which can serve as template layer to integrate manganites onto appropriate semiconductors for device applications.

La1−xBaxMnO3 epitaxial thin films by pulsed-laser deposition: A consequence of strain stabilization

We report transport, magnetization, and transmission-electron-microscopic studies of La1−xBaxMnO3/SrTiO3 thin films grown by pulsed-laser deposition. The metal–insulator transition is remarkably sharp, and the high value of the temperature coefficient of resistivity is significantly relevant for the required value for the infrared imaging applications. We have demonstrated that the strain-induced property can be tuned and stabilized in La1−xBaxMnO3 films simply by changing the doping level (La/Ba ratio) and addition of metal ions (Ag) for applications at desirable temperature regime close to room temperature.

Colossal magnetoresistance in doped manganites: A consequence of percolation and phase separation

We report measurements of the resistivity and magnetization of high-quality melt-processed La0.67Ca0.33MnO3 (LCM) and Sr-doped LCM materials that exhibit a sharp and enhanced metal–insulator transition (TMI) with significant colossal magnetoresistance (CMR) and two competing magnetic phases in the vicinity of TMI. Our results can well be explained using percolation in combination with the phase-separation scenario proposed for CMR. We propose that the spin polarization through grain boundaries and the enhanced grain connectivity between the ferromagnetic domains facilitate better percolation through a junction and filament-like resistor network.

Junction characteristics of SrTiO3 or BaTiO3 on p-Si (100) heterostructures

The authors report the fabrication of p-n junctions, consisting of n-type SrTiO3 or BaTiO3 and p-type Si substrates, by the pulsed-laser deposition technique. The BaTiO3∕Si junction exhibits excellent rectifying behavior and significantly reduced leakage current at 300K exceeding breakdown voltage of −25V with leakage current <0.5μA, while SrTiO3∕Si with an interfacial layer shows moderate junction characteristics. It was demonstrated that the BaTiO3∕Si grown at an optimum growth temperature of 650°C displayed superior performance which is promising for electronic devices. Both junctions show photocurrent at 300K due to electron injection following the photoexcitation of n-type perovskite.

Studies on dielectric properties of Al–Zr oxide composites sintered by thermal plasma

Abstract High-density sintered product of Al x –Zr 100− x ( x =0, 10, 20,…100) composites were produced using low-cost extended arc thermal Plasma heating (EATPH) source. Dielectric properties of these samples were studied as a function of different frequencies and at different temperatures. Particle sizes and density of the plasma-sintered products were controlled by controlling the plasma power, sintering time and plasmagen gas flow rate during sintering. Morphology and structure of sintered Al–Zr samples were examined by SEM and X-ray diffraction (XRD) to understand the plasma-sintered induced dielectric properties. It is noted that frequency- and temperature-dependent dielectric constant and loss factors are the consequence of polarization of dipole moment, which varied with the variation of plasma-sintered particle size. It is also observed that surface charge polarization along with dipole screening play crucial role at higher frequencies and at higher temperature. Dipole pinning and depinning mechanism are proposed to explain this complicated dielectric behavior.

Manganite-based magnetic tunnel junction with piezoelectric barrier

We report on the fabrication and tunneling characteristics of pulsed-laser deposited LaSrMnO (LSMO)∕PbZrTiO(PZT)∕LSMO∕SrTiO3 multilayers, using PZT layer as a tunnel barrier. The trilayer films show magnetic onset at about 360K with ferromagnetic hysteresis at room temperature. The microscopic studies show that the effective barrier thickness is reduced due to the presence of defects in the barrier region. Our results suggest that the asymmetric deformation of the barrier potential profile induced by the ferroelectric polarization of PZT influences the tunneling characteristics and can be used for electrically controlled readout in quantum-computing schemes.

Growth and properties of PZT -based perovskite multilayers for sensor applications

We have studied ferroelectric properties of Pb (Zr0.6Ti0.4) O3(PZT)/SrTiO3 thin films grown on platinized silicon substrates using pulsed-laser deposition and magnetron sputtering technique. The spontaneous polarization (Ps) and remnant polarization (Pr) varies between 15.5 K and 100 K from 33-38 μC/cm2 and 25-30 μC/cm2,respectively. Similar values of Ps and Pr were also observed until temperature reached to 300K. However, more pronounced ferroelectric hysteresis loops were observed between T= 323 to 353 K. The Ps and Pr remain around 36-40 μC/cm2and 23-28 μC/cm2, respectively, between T = 323 to 353 K. The remnant polarization remains fairly consistent over the chosen temperature range. X-ray diffraction and high-resolution microscopic studies reveal that the Pb (Zr0.6Ti0.4) O3 layers are superior in crystalline quality than that of SrTiO3. The PZT in multilayered films show remarkably enhanced polarization properties relative to their single layers on the same substrates. The collective contribution of dipole moments from each layer is the reason for such enhancement in polarization properties. This growth strategy may be very useful for fabrication of sensitive sensing and other relevant devices.