S. I. Patil

Evaluation of manganite films on silicon for uncooled bolometric applications

Pulsed-laser-deposited polycrystalline/amorphous films of mixed-valent manganites [La0.7Ca0.3MnO3 (LCMO), La0.5Sr0.5MnO3 (LSMO), La0.5Ba0.5MnO3 (LBMO), and (La0.6Pr0.4)0.67Ca0.33MnO3 (LPCMO)] grown at low temperature (450 °C) on single crystal (001) silicon substrate are evaluated for uncooled bolometric applications. It is shown that the temperature coefficient of resistance (TCR) and electrical noise (Sv) depend on the chemical composition. The optimum performance is found for LCMO with TCR of ∼7% K−1 and spectral noise ∼8.9×10−13 V2/Hz. In LBMO and LSMO the noise is much lower, but so is the TCR (1.5%–2% K−1). In LPCMO the TCR is high (∼10% K−1) and the noise is as well.

Silver ion implantation in epitaxial La2/3Ca1/3MnO3 thin films: Large temperature coefficient of resistance for bolometric applications

Epitaxial films of La2/3Ca1/3MnO3 were successively implanted with 100 and 200 keV silver ions at fluences of 4.5×1015 and 1×1016 ions/cm2, respectively, to achieve a fairly uniform implant distribution. The as-implanted films are insulating and do not show a metal–insulator transition. Postimplantation annealing at 950 °C shows a recovery of the high structural quality of the films, along with an increase in the metal–insulator transition temperature (Tp), magnetoresistance, and the peak temperature coefficient of resistance (TCR) at the transition. The peak TCR of 23% for manganite films is clearly significant for bolometric applications.

Structural, electrical transport, magnetization, and 1∕f noise studies in 200MeV Ag ion irradiated La0.7Ce0.3MnO3 thin films

The effect of 200MeV Ag ion irradiation on structural, electrical transport, magnetization, and low-frequency conduction noise properties of electron-doped La0.7Ce0.3MnO3 thin films have been investigated. The as-grown thin films show c-axis epitaxial structure along with a small amount of unreacted CeO2 phase. After the irradiation, at the lowest fluence both the magnetization and metal-insulator transition temperature increase. Further increase in fluence reduces the metal-insulator transition temperature and leads to larger resistivity; however, the unreacted phase of CeO2 disappears in the x-ray diffraction pattern. On the other hand, the normalized electrical noise is greatly enhanced even at the lowest nonzero fluence. Surprisingly the conducting noise in the irradiated samples is much higher in the metallic state than in the semiconducting one. The observed modifications in structural, electrical, magnetic, and noise properties of 200MeV Ag ion irradiated La0.7Ce0.3MnO3 thin films have been explain...

Swift heavy ion irradiation effects on transport properties of epitaxial thin films of La1-xCaxMnO3

Abstract The influence of swift heavy ion (SHI) irradiation on transport properties of epitaxial thin films of La0.75Ca0.25MnO3 (LCMO) is studied. The films were irradiated with 90 MeV16O beams and 250 MeV107 Ag beams at different fluence values. In the case of 90 MeV16O ions LCMO specimens were irradiated to 1011-1014 ions/cm2 and for 250 MeV107Ag ions with 1010–1013 ions/cm2. A systematic variation in Curie temperature (T c) or resistivity peak temperature (T p) has been observed. It has been noted that for both types of ions the T p increased for the specimen irradiated at 1011 ions/cm2 fluence. Further increase of fluence decreased the T p value and at higher fluence (1014 ions/cm2 for 90 MeV16O and 1013 ions/cm2 for 250 MeV107 Ag ions) the specimens showed no metal-to-insulator transition even at low temperature down to 77K. They show completely semiconducting behavior with high resistance values. These results are discussed in terms of SHI irradiation-induced structural distrotion and strain on thin...

Enhanced magnetic and bolometric sensitivity of La0.7Ce0.3MnO3 thin films due to 200 MeV Ag ion irradiation

The parameters for bolometric performance [temperature coefficient of resistance (TCR) and noise value] and magnetic sensitivity of pulsed-laser-deposited thin films of La0.7Ce0.3MnO3 and their dependence on the 200 MeV Ag ions irradiation are studied. It is observed that the TCR value and magnetic sensitivity can be tuned in different temperature regime by controlling the irradiation fluence value. It turns out that irradiation with a fluence value of 5×1010ions∕cm2 changes the TCR value in a positive direction and enhances magnetic sensitivity at room temperature, while irradiation with a fluence value of 1×1012ions∕cm2 enhances these parameters at 200 K. The observations are explained on the basis of structural and electrical transport modifications induced by the 200 MeV Ag ion irradiation.

Exposition of semiconducting and ferromagnetic properties of pulsed-laser-deposited thin films of LaFe1-xNixO3 (x=0.3, 0.4, and 0.5)

We have explored the possibility of ferromagnetic semiconducting property in the epitaxial thin films of LaFe1−xNixO3 (x=0.3, 0.4, and 0.5) grown on (001) oriented LaAlO3 substrate. We observe that substitution of Ni in the series leads to the increase in conductivity of the samples with conduction being controlled by the disorder-induced localization of charge carriers. All these samples show ferromagnetic behavior at room temperature while their magnetization decreases with increase in Ni concentration in the composition. The results have been explained on the basis of the close interplay between the electrical and magnetic properties.

90 MeV 16O ion irradiation effects on transport and magnetization in epitaxial thin films of La0.75Ca0.25MnO3

The influence of 90 MeV 16O ion irradiation on the electric and magnetic properties of epitaxial thin films of La0.75Ca0.25MnO3 is studied. These films were deposited on LaAlO3(100) substrates by the pulsed excimer laser deposition technique. The thickness of each film was about 3000 A. The high quality of the films was ensured by x-ray diffraction and transport measurements. The films were irradiated with 90 MeV oxygen ions at different doses (1011–1014 ions/cm2). It is observed that at a low dose of 1011 ions/cm2 the resistivity peak temperature (Tp) and the Curie temperature (Tc) increase, however as the dose is increased further, the Tp and Tc decrease. At the higher dose of 1014 ions/cm2, the film becomes insulating and does not show any peak in the resistivity–temperature curve down to 60 K. These results are discussed in terms of the effects of ion induced compositional inhomogeneity and strain on the film properties.

Effect of iron doping on electrical, electronic and magnetic properties of La0.7Sr0.3MnO3

The effect of 5% Fe doping at Mn site, on the valence band structure of La0.7Sr0.3MnO3 has been investigated. Polycrystalline samples of La0.7Sr0.3MnO3 and La0.7Sr0.3Mn0.95Fe0.05O3 have been prepared by the solid-state reaction route. The phase purity of these samples was confirmed using x-ray diffraction. Core-level x-ray photoelectron spectroscopy measurements were performed to study the changes in the chemical composition. The valence band spectroscopy measurements on these samples, using a synchrotron radiation source, show a considerable change in the density of states (DOSs) at the Fermi level with 5% Fe doping. The results are correlated with room temperature resistivity and magnetization data on these samples. These results suggest that though the DOSs at the Fermi level increase on Fe doping, the conduction in LSMO gets hampered. This may be a result of changes in the hybridization of the orbitals due to Fe doping which modifies the MnO6 octahedra and hence the Mn3+–O–Mn4+ network.

Columnar defect induced phase transformation in epitaxial La0.7Ca0.3MnO3 films

Epitaxial La0.7Ca0.3MnO3 thin films on the SrTiO3(100) surface have been irradiated with 250 MeV Ag17+ ions at different nominal fluence values in the range of 5×1010–4×1011 ions/cm2, resulting in columnar defects. At low fluences these defects cause changes in material properties that are small and scale linearly with dosage. Above a threshold fluence value ∼3×1011 ions/cm2 dramatic changes are observed, including an order of magnitude increase in the resistivity and 50 K drop in the Curie temperature. Transmission electron microscopy measurements show that the changes are associated with a phase transformation of the undamaged region between the columnar defects. The transformed phase has a diffraction pattern very similar to that seen in charge-ordered La0.5Ca0.5MnO3. We propose that above a critical level of ion damage, strains caused by the presence of the columnar defects induce a charge-ordering phase transition that causes the observed dramatic changes in physical properties. We speculate that a c...

Structural, morphological, and electrical characterization of heteroepitaxial ZnO thin films deposited on Si (100) by pulsed laser deposition : Effect of annealing (800 °C) in air

Pulsed laser deposition technique was used for growing thin films of ZnO on Si (100) substrate held at different temperatures (Ts). All the as-deposited films have shown a preferential c-axis orientation associated with varying grain size as a function of Ts ranging from 100to600°C. Current-voltage (I-V) characteristics of these films show Ohmic behavior over the entire Ts range studied. These films were subjected to annealing at 800°C in air ambient for 4h. The grain size was observed to increase after the annealing process for all the films deposited at different Ts. Interestingly, these annealed films show nonlinear variation of current with applied voltage, very similar to the one observed in doped ZnO varistors. The nonlinear parameters such as the asymmetric behavior of change in current on the polarity reversal of voltage, the plateau region, and the break down voltage are observed to depend on Ts. This nonlinear behavior can perhaps be explained on the basis of electronic conduction model proposed...