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The growth of strongly oriented or epitaxial thin films of metal oxides generally requires relatively high growth temperatures or infusion of energy to the growth surface through means such as ion bombardment. We have grown high quality epitaxial thin films of $Co_3O_4$ on different substrates at a temperature as low as 450° C by low pressure metal organic chemical vapor deposition (MOCVD) using cobalt(II) acetylacetonate as the precursor. With oxygen as the reactant gas, polycrystalline $Co_3O_4$ films are formed on glass and Si(100) in the temperature range 350 550° C. Under similar conditions of growth, highly oriented films of $Co_3O_4$ are formed on $SrTiO_3(100)$ and $LaAlO_3(100)$. The film on $LaAlO_3(100)$ grown at 450° C show a rocking curve FWHM of 1.61°, which reduces to 1.32° when it is annealed in oxygen at 725° C. The film on $SrTiO_3(100)$ has a FWHM of 0.33° (as deposited) and 0.29° (after annealing at 725° C). The φ-scan analysis shows cube on cube epitaxy on both these substrates. The quality of epitaxy on $SrTiO_3$ (100) is comparable to the best of the perovskite basedoxide thin films grown at significantly higher temperatures

We report on the growth of La 0.8 Ce 0.2 MnO 3 thin films on (0 0 1) LaAlO 3 substrates by pulsed laser deposition. CeO 2 as an impurity is present in both the bulk and film samples. The electrical transport and magnetic properties of the films are similar to that of the divalent cation-doped or La deficient LaMnO 3 , which show colossal magnetoresistance. Thermopower measurements indicate that the carriers are holes. The results are explained in terms of a La site deficiency due to the existence of CeO 2 .

We report on the structural, transport, and magnetic properties of ${\mathrm{La}}_{0.67}{\mathrm{Sr}}_{0.33}{\mathrm{MnO}}_{x}$ thin films grown in vacuum by pulsed-laser deposition. The as-grown thin films have both the matrix ${\mathrm{La}}_{1.34}{\mathrm{Sr}}_{0.66}{\mathrm{MnO}}_{4}$ phase with ${\mathrm{K}}_{2}{\mathrm{NiF}}_{4}$ structure and an embedded MnO phase. The electrical transport and magnetic properties of the films are determined mainly by those of the matrix phase. By annealing, the as-grown thin films can be transformed into the normal ${\mathrm{La}}_{0.67}{\mathrm{Sr}}_{0.33}{\mathrm{MnO}}_{3}$ single phase, which shows the expected colossal magnetoresistance effect. Based on the composition of the matrix phase, and the structural, electrical, and magnetic properties of the films, we propose that the matrix phase is possibly electron doped with a mixed valence of ${\mathrm{Mn}}^{2+}{/\mathrm{M}\mathrm{n}}^{3+}$ instead of the ${\mathrm{Mn}}^{3+}{/\mathrm{M}\mathrm{n}}^{4+}$ as in the hole-doped case.

This paper examines the possibility of enhancing the room temperature magnetoresistance at low applied magnetic fields in single layer La0.7 Ba0.3 MnO3 thin films. The influence of lattice mismatch strain, as well as the effect of different frequency regimes, on the magnetoresistance is explored. The effects of lattice mismatch strain are studied by measuring the magnetoresistance as a function of the La0.7 Ba0.3 MnO3 film thickness, oxygen annealing, and lattice matched buffer layers. We find that the release of the lattice mismatch strain improves the magnetoresistance at room temperature and at low magnetic fields. In fact, the highest magnetoresistance at room temperature (−1.7% at 500 Oe) has been found for the 1600 A as-grown La0.7 Ba0.3 MnO3 film, whereas the largest magnetoresistance (−1.9% at 500 Oe) is found at 309 K for the 1000 A La0.7 Ba0.3 MnO3 film annealed in flowing O2 for 1 h at 900°C. Finally, we find that the microwave magnetoresistance is the same as the dc magnetoresistance when the cavity corrections are applied. In the single layer La0.7 Ba0.3 MnO3 system, the low field magnetoresistance at room temperature is far from being technologically viable.

(110) oriented La1−δMn1−δO3 thin films with different oxygen content were grown on (001) LaAlO3 substrates by pulsed laser deposition. Samples prepared in higher oxygen partial pressures show a ferromagnetic transition around 200 K. The transport is thermally activated with a change in slope at the ferromagnetic transition. Samples prepared and annealed in vacuum show signatures of mixed ferromagnetic and antiferromagnetic phases, and are insulators. The pure antiferromagnetic phase (as expected and observed in bulk materials with optimum oxygen stoichiometry) was not obtained in our experiments, even in the strongly reduced films.

The transient photoimpedance response of epitaxial YBa2Cu3O7−δ thin films has been studied using 100 fs Ti:Sapphire laser pulse excitation. Both temperature and photon energy dependence of the fast optical response signal (whose temperature dependence can be explained by a kinetic inductance model involving Cooper pair breaking) were studied. The pair breaking rate is strongly photon energy-dependent, with a resonance around 1.5 eV with a width of only 100 meV, which is very surprising given the strong electron correlation in this metallic system and may be explained in terms of the stripe phase model.

Epitaxial films of La0.7Ca0.3MnO3 have been irradiated with 90 MeV oxygen ions at different dose values ranging from 1011–1014 ions/cm2. The structural, magnetization, and magnetotransport properties have been studied as a function of the ion dose. It is found that the properties change gradually up to a dose of 1013 ions/cm2; however, drastic changes occur when the sample is irradiated at the higher dose of 1014 ions/cm2. Specifically, this sample exhibits a large, nearly temperature independent magnetoresistance in the low temperature regime. The Rutherford backscattering channeling data bring out the presence of defects in the irradiated films. The x-ray diffraction data, the temperature dependence of resistivity and magnetization, and the low temperature magnetic hysterisis data collectively indicate the presence of two different phases in the sample irradiated at 1014 ions/cm2. The surface morphology of this film, observed by atomic force microscopy, exhibits swelling, presumably due to subsurface cl...

We have prepared single phase ${\mathrm{PrBa}}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7}$ ($x=0,$1.3,1.6) thin films with dopant concentration exceeding the solid solubility limit by using the pulsed laser deposition method. The resistivity of the doped thin films decreases with increasing dopant concentration. For $x=1.3,$ the electrical resistivity ratios $\ensuremath{\rho}(4.2\mathrm{}\mathrm{K})/\mathrm{\ensuremath{\rho}}(300\mathrm{}\mathrm{K})=2.56;$ while for $x=1.6,$ $\ensuremath{\rho}(4.2\mathrm{}\mathrm{K})/\mathrm{\ensuremath{\rho}}(300\mathrm{}\mathrm{K})=1.98,$ comparable to that of the ${\mathrm{Y}}_{0.5}{\mathrm{Pr}}_{0.5}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7}$ sample, which is very close to the insulator-metal transition. Moreover, the resistivity of the ${\mathrm{PrBa}}_{0.4}{\mathrm{Sr}}_{1.6}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7}$ thin film is very close to the Ioffe-Regel limit, also indicating its proximity to the insulator-metal transition. The decrease of the resistivity with doping for ${\mathrm{PrBa}}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7}$ can be explained by the decrease of the hybridization between Pr $4f$ and O $2p$ states in the ${\mathrm{CuO}}_{2}$ planes due to the Sr doping induced increase of the Pr-O bond length.

The effect of laser power on the transient response of photoimpedance and the in situ sample temperature is studied for epitaxial YBa2Cu3O7−δ (YBCO) films at a wavelength of 810 nm using 100 fs laser pulses. The temperature dependences of the dc resistance and the amplitudes of the fast and slow photoresponse signals were measured simultaneously. For laser energy density of 20 μJ/cm2 per pulse (average power 22 mW), the average sample temperature is found to increase by about 1 K for 300 nm thick YBCO film with 0.5 mm thick LaAlO3 substrate as shown by the shift of resistance versus temperature curves. Calculations of time constant show that heat diffusion in LaAlO3 is the bottleneck for heat escape which causes the observed increase of the sample temperature. The amplitudes of both slow and fast signals show a peak in the temperature dependence curves near the superconducting transition temperature; and the peak temperature decreases, while the peak amplitude increases with laser power. At 82 K, the lase...

We have measured the angular dependence of the critical current density (J{sub c}) on magnetic field and temperature in untwinned a-axis-oriented YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} films. The direction of magnetic field with respect to the crystallographic axes was found to be the dominant factor determining the behavior of J{sub c}. J{sub c}({theta}) measurements, for currents driven along the b direction, yielded a peak at 0{degree} corresponding to the magnetic field applied parallel to the CuO{sub 2} planes. For supercurrents flowing along the c direction, a crossover from grain-boundary pinning to surface and interface pinning was observed as temperatures approached T{sub c}. Lawrence-Doniach and Tinkham H{sub c2}({theta}) models were used to fit our J{sub c}({theta}) data by simply replacing H{sub c2}({theta}) with J{sub c}({theta}). These models fit our J{sub c}({theta}) data very well, at high and medium-to-low temperature ranges, respectively. {copyright} {ital 1997} {ital The American Physical Society}

We studied the effects of Co doping on the intrinsic anisotropic properties of aligned a-axis YBa/sub 2/Cu/sub 3-x/Co/sub x/O/sub 7-/spl delta// films pulsed laser deposited on (100) LaSrGaO/sub 4/ substrates We used X-ray-absorption fine structure analysis and resistivity data to determine the quality of Co incorporation. Higher deposition pressures provided with better Co dopant incorporation but smaller grain size. However at lower pressures Co incorporation can still be achieved by down the cooling process. For transport along the c-direction, Co dopant causes reduction interlayer coupling as evidenced by an increase resistive anisotropy (/spl rho//sub c///spl rho//sub b/) with increasing level of Co incorporation, Co doping level of x=0.22 effectively doubles the resistive anisotropy of YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// films (from -18 to -40 at 100 K).

The normal state and transition edge optical response of epitaxial thin films of n-type superconductor Nd/sub 1.85/Ce/sub 0.15/CuO/sub 4-y/ has been measured. In contrast to the optical response of p-type superconductors such as YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// the normal state optical response of these films were not proportional to the temperature derivative of the resistance. The normal state optical response of films with different transition temperature (and, therefore, different oxygen content) were also remarkably different from each other. We attribute the observation of anomalous optical response to the possible presence of photoconductivity in Nd/sub 1.85/Ce/sub 0.15/CuO/sub 4-y/. We also discuss the feasibility of fabricating bolometers based on superconducting p-n bilayers. >

We have measured the microwave magnetoabsorption of both pristine and irradiated c-axis-oriented YBa/sub 2/Cu/sub 3/O/sub 7/ thin films. The irradiation was done using 270-MeV Ag ions and produces columnar defects along the film normal. The angular dependence of the absorption for pristine films can be described by sin/spl theta/; where /spl theta/ is the inclination of the field from the film plane. However, there is a minimum in the magnetoabsorption of the irradiated films when the applied field is parallel to the columns. This minimum is indicative of vortex localization as predicted by Nelson and Vinokur. We believe that this is the first high-frequency measurement of this phenomenon. >

Epitaxial c-axis-oriented thin films of Fe- or Zn-doped YBa 2 Cu 3 O 7-δ have been grown on (001) LaAlO 3 substrates by pulsed excimer laser ablation. Adequate substitutional incorporation of Fe atoms required optimal choice of oxygen pressure during deposition as well as a postsynthesis annealing treatment at 550 °C. Zn incorporation did not require such special processing conditions. The resistivity transitions for such high-quality well-characterized films were studied at different magnetic fields up to 5 T. Analysis of T c depression and change in dH c2 /dT at T c has been made in terms of the possible changes in the density of states at the Fermi level, contributions of the exchange field, magnetization field, and nonmagnetic scattering. Estimates of the activation energy [U 0 (H)] for vortex motion have also been made.

The far-infrared transmission of YBa2Cu3O7−δ films with columnar defects produced by high-energy ion irradiation has been measured from 20 to 150 cm-1 at 6 K in magnetic fields of 0–9 T. The change in transmission produced by irradiation can be understood by modeling the columnar defects as normal-metal or insulating cylinders in a superconducting background. Magnetic field induced spectral structure near 60 cm-1 in the pristine samples is suppressed by a defect density equal to the density of vortices at that field. However, the magneto-transmission above 60 cm-1 is nearly unaffected by the irradiation process. We discuss these results in terms of the current understanding of the nature of vortices and columnar defects in YBa2Cu3O 7−δ.

We report the angular magnetic-field dependence of the critical current density in epitaxial thin films of Nd 1.85 Ce 0.15 CuO 4-δ in the temperature range 1.4 K to 14 K. At low temperatures, the critical current anisotropy is well described by the 2D model of Josephson-coupled layers. Above 10 K we observe deviations from the 2D behavior which may be attributed to the temperature dependence of the coherence lenght and the influence of the anisotropy of the upper critical field. The field dependence of the critical current density for the field orientation parallel to the CuO 2 planes is consistent with the dimensionality indicated by the angular dependence.

The angular magnetic field dependence of the critical current density JC(θ) of epitaxial YBa2Cu3O7 thin films is presented in the temperature regime close to Tc. The high temperature behavior of Jc(θ) shows features that are significantly different from the earlier observations at lower temperatures. A comparison between the films on (100) LaAlO3 and (100) yttria stabilized zirconia (YSZ) indicates significant differences that may be attributed to the differences in the microstructure of the films on the two substrates. In particular, the observation of enhanced pinning in the films on YSZ may be due to the pinning effects of the low angle grain boundaries present in these films.

Anisotropie surface texturing of the polycrystalline yttria-stabilized zirconia substrates, prior to YBa2Cu3O7−x film deposition, is shown to promote in-plane (basal plane) ordering of the film growth in addition to thec-axis texturing. TheJ c 's of the films in the weak-link-dominated low-field regime are enhanced considerably, and this result is attributed to the reduction of weak links resulting from a reduction in the number of in-plane large-angle grain boundaries.

Epitaxial thin films of ordered double-perovskite Sr2FeMoO6−y are deposited on (001) SrTiO3 substrates by pulsed-laser deposition using a two step growth process. Selection of growth conditions is found to lead to either highly conductive metallic thin films (residual resistivity of about 1 μΩ cm) or semiconducting films. The metallic films show a positive magnetoresistance (MR) as high as 35%, while the semiconducting films show a negative MR of −3%, at a temperature of 5 K and a field of 8 T.

Anomalously high metal–insulator transition temperature Tp and ferromagnetic transition temperature Tc have been observed in thin films of La0.8Ca0.2MnO3. Ferromagnetic resonance signals from microwave studies are observed at room temperature (well above Tc) suggesting the presence of multiple magnetic spin systems. The Tp and Tc values are higher than that of La0.67Ca0.33MnO3 which have the highest Tp and Tc according to the bulk phase diagram. These results suggest that properties well beyond those seen in the bulk phase diagram may be achievable in thin films of the manganites.

We report measurements of the alternating current (ac) magnetic susceptibility, χac=χ′+iχ″, performed on colossal-magnetoresistance (CMR) materials. We have studied thin film samples of La0.67Ca0.33MnO3 and Nd0.7Sr0.3MnO3. For homogeneous samples, the temperature of the peak observed in χ″(T) is in agreement with the temperature of peak resistivity (TP) obtained from transport measurements. This agreement is not found for inhomogeneous samples, where χ″(T) shows multiple peaks. The analysis of χ″(T) enables one to determine the quality of the CMR materials. The results obtained in thin films of La0.67Ca0.33MnO3 and Nd0.7Sr0.3MnO3, are consistent with those obtained from an homogeneous single crystal of La0.80Sr0.20MnO3. We show that the contactless ac magnetic susceptibility technique is a quick method to reveal inhomogeneities which are not directly evident in direct current transport measurements.

Single-phase PrBa0.7Sr1.3Cu3O7 thin films with the Sr dopant concentration exceeding the solid solubility limit were epitaxially grown on (001) SrTiO3 and (001) LaAlO3 substrates by pulsed laser deposition (PLD) method. The resistivity of the doped films grown on LaAlO3 was significantly lower than that of PrBa2Cu3O7. For most of the films grown on SrTiO3, the resistivity was higher than that of PrBa2Cu3O7. The results were explained by considering the Sr-doping effect and lattice-mismatch-induced strain effect. This work shows the potential of PLD to grow single-phase films with the dopant concentration exceeding the solid solubility limit.

We report our study of the effect of crystallinity on the magnetoresistance in epitaxial and polycrystalline La2/3Ba1/3MnO3 and La2/3Ca1/3MnO3 thin films. Magnetoresistance in epitaxial films exhibits field dependence and temperature dependence similar to bulk single crystals and sintered bulk ceramics. The polycrystalline films exhibit a markedly different behavior. The magnetoresistance in this case shows either a monotonic increase or saturation with decreasing temperature in contrast to that of epitaxial films in which the magnetoresistance peaks close to the ferromagnetic transition temperature. The field dependence in the polycrystalline films is also remarkably different. At low fields, we observe a sharp drop in resistance followed by a more gradual decrease at higher fields. Our data suggest that in addition to the intrinsic magnetoresistance, grain-boundary transport contributes significantly to the magnetoresistance in polycrystalline films.

Thin films of colossal magnetoresistance (MR) material, La0.67Ca0.33MnO3, were implanted with different doses (1011–1015 ions/cm2) of 200 keV Ar+ ions. The implanted samples were examined by ion channeling and x‐ray diffraction techniques. The channeling results clearly showed that the magnitude of the induced lattice disorder did not increase greatly for implantation doses up to 5×1013 ions/cm2. In this low dose implantation regime, the magnetoresistance {MR=[R(0)−R(H)]/R(0)} increased by 50%, the peak resistivity went up by two orders of magnitude, and the magnetoresistivity peak temperature decreased by 130 K compared to the original, unimplanted sample. For doses ≥5×1013 ions/cm2, the damage was significant and caused the sample to become semiconducting.

We are able to grow high quality La0.67Sr0.33MnO3(LSMO) colossal magnetoresistive (CMR) thin films on Y‐stabilized zirconia (YSZ) buffered (100) Si substrates using a Bi4Ti3O12 texturing and lattice matching layer. The CMR films have very high structural perfection and show excellent transport and ferromagnetic properties, including the almost full saturation magnetization values and narrow ferromagnetic resonance peaks (15 Oe at 290 K). The lattice matching template/buffer layer approach is suitable for the high quality CMR films on Si. A close correlation between the magnetic hysteresis loop and the field dependence of MR is observed at lower temperatures.

We report measurements of the low‐frequency optical response in epitaxial thin films of La0.67Ca0.33MnO3 in the temperature range covering both the ferromagnetic metallic state and the paramagnetic insulating state. We observe a bolometric optical response in fully oxygenated films of the above composition as well as in oxygen deficient films. In both types of samples, the optical response is thermal in nature as indicated by its proportionality with the temperature derivative of the resistance dR/dT.

High quality epitaxial YBa2Cu3O7−x (YBCO) thin films have been deposited onto ferrimagnetic yttrium iron garnet (100) substrates using a double buffer layer lattice engineering scheme. The YBCO films are c‐axis oriented and show superconductive transition temperatures of 88–89 K with transition widths ≤0.5 K. The films also exhibited Jc’s of 2.7×106 A/cm2 in zero field and 1.1 ×106 A/cm2 in 2000 G at 77 K. Dielectric resonator measurements indicated unloaded Q values of 29 000 at 77 K and 24 GHz for unpatterned films. These values correspond to a surface resistance (RS) of 500 μΩ at 77 K, 10 GHz, which is the lowest obtained to date for a YBCO film on a ferrimagnetic substrate. Such films could be used for fabricating miniature‐high‐temperature superconducting microwave elements such as nonreciprocal and passive microwave devices, making possible, their integration on a single ferrimagnetic wafer.

Incorporation of Fe in YBa2Cu3O7−δ matrix during its epitaxial growth on (001) LaAlO3 by pulsed excimer laser ablation is examined. It is shown that oxygen pressure during deposition plays a critical role in the incorporation process and that a low‐temperature postsynthesis annealing is essential for complete substitution. Clustering of iron atoms and its control via the anion controlled reactions are identified as the key features in this context. It is also shown by using atomic force microscopy that Fe incorporation influences the surface morphology. These issues are of importance in the formation of cationic defects in multicomponent thin films.

Investigations of incoherent lattice fluctuations and electrical transport in oxygen isotope substituted ${\mathrm{Nd}}_{0.67}{\mathrm{Sr}}_{0.33}{\mathrm{MnO}}_{3}$ thin films have shown an increase in the incoherent displacement of the Mn atoms as the sample goes from the ferromagnetic to paramagnetic state. The observed enhancement is about 15% larger and occurs over a \ensuremath{\sim}12% narrower temperature range for ${}^{18}\mathrm{O}$ than for ${}^{16}\mathrm{O}.$ The peak in resistivity, which is close to the magnetic phase transition, is enhanced in intensity and shifted to lower temperatures by about 25 K for ${}^{18}\mathrm{O}$ films as compared to the ${}^{16}\mathrm{O}$ films. The different behavior for the two oxygen isotopes demonstrates the importance of quantum fluctuations of the O phonon on the magnetic phase transition in this system.

We present evidence for the coexistence of ferromagnetic metallic and charge-ordered insulating phases in strained thin films of ${\mathrm{La}}_{0.67}{\mathrm{Ca}}_{0.33}{\mathrm{MnO}}_{3}$ at low temperatures. Such a phase-separated state is confirmed using low-temperature magnetic force microscopy and magnetotransport measurements. This phase separated state is not observed in the bulk form of this compound and is caused by the structural inhomogeneities due to the nonuniform distribution of strain in the film. The strain weakens the low-temperature ferromagnetic metallic state and a charge-ordered insulator is formed at the high strain regions. The slow dynamics of the transport properties of the mixed phase is illustrated by measurements of the long-time scale relaxation of the electrical resistance.

The growth of strongly oriented or epitaxial thin films of metal oxides generally requires relatively high growth temperatures or infusion of energy to the growth surface through means such as ion bombardment. We have grown high quality epitaxial thin films of Co3O4 on different substrates at a temperature as low as 450°C by low-pressure metal-organic chemical vapor deposition (MOCVD) using cobalt(II) acetylacetonate as the precursor. With oxygen as the reactant gas, polycrystalline Co3O4 films are formed on glass and Si(100) in the temperature range 350-550°C. Under similar conditions of growth, highly oriented films of Co3O4 are formed on SrTiO3(100) and LaAlO3(100). The film on LaAlO3(100) grown at 450°C show a rocking curve FWHM of 1.61°, which reduces to 1.32° when it is annealed in oxygen at 725°C. The film on SrTiO3(100) has a FWHM of 0.330 (as deposited) and 0.29° (after annealing at 725°C). The ø-scan analysis shows cube-on-cube epitaxy on both these substrates. The quality of epitaxy on SrTiO3(100) is comparable to the best of the pervoskite-based oxide thin films grown at significantly higher temperatures.

Textured polycrystalline YBCO films with superconducting transition temperatures of ∼90 K have been prepared on flexible zirconia substrates, partially stabilized by 3 mol % yttria. X‐ray data suggest undesirable (013) and [(110) (103)] texture in minor amounts within the predominantly c‐axis oriented film. The transmission electron microscope data reveal clean, special crystallographic as well as silicon contaminated grain boundaries containing amorphous phases. By depositing a zirconia buffer layer, fully stabilized by 9 mol % yttria, we have demonstrated that the normal‐state metallic and superconducting properties of the YBCO films can be considerably improved. These films exhibit critical‐current densities of ∼0.9×104 A/cm2 at 77 K in zero field and 2×105 A/cm2 at 4.2 K in zero field.

We report the synthesis and characterization of Nd_{0.5}Sr_{0.5}MnO_{3} thin films grown by the Pulsed Laser Deposition technique on 100 -oriented LaAlO_{3} substrates. X-ray diffraction (XRD) studies show that the films are 101 -oriented, with a strained and quasi-relaxed component, the latter increasing with film thickness. We observe that transport properties are strongly dependent on the thickness of the films. Variable temperature XRD down to 100 K suggests that this is caused by substrate induced strain on the films., Comment: 3 pages REVTeX, 4 figures included, submitted to APL

We report the growth and characterization of Nd0.5Sr0.5MnO3 thin films deposited by the Pulsed Laser Deposition (PLD) technique on [100]-oriented LaAlO3 substrates. X-ray diffraction (XRD) studies show that the films are [101]-oriented, with a strained and quasi-relaxed component, the latter increasing with film thickness. A post-annealing under oxygen leads to a quasi-relaxed film with a metallic behavior. We also observe that transport properties are strongly dependent on the thickness of the films. Variable temperature XRD down to 100 K suggests that this is caused by substrate-induced strain on the films.

Oriented, single phase thin films of La_{1-x}Ca_{x}MnO_{3} have been deposited onto (100)-oriented LaAlO_{3} (0.1, Comment: 8 pages, 5 figures submitted to Applied Physics Letters

We have investigated the optical response of single grain-boundary weak-links in superconducting YBCO thin films. At the superconducting transition of a film containing a single grain-boundary weak-link we observed an enhanced optical response from the weak- link. Below the transition temperature, we measure the bias current and the temperature dependence of the optical response of the grain-boundary in the temperature range of 15 K < T < 80 K. Using a Resistively-Shunted-Junction model for the grain-boundary weak- link, we find that the optical response in this temperature range can be described by radiation induced thermal modulation of the critical currents.

We have performed depth profile analyses of the lattice parameters in epitaxial thin films of La0.67Ca0.33MnO3 to understand the evolution of strain relaxation processes in these materials. The analyses were done using grazing incidence x-ray scattering on films of different thicknesses on (100)-oriented LaAlO3 with a lattice mismatch of −2%. We find that such films exhibit two and sometimes up to three in-plane strained lattice constants, corresponding to a slight orthorhombic distortion of the crystal, as well as near-surface lattice relaxation. As a function of film thickness, we find that the strain is in the same order of magnitude up to a thickness of 70–80nm, after which the strain begins to relax towards the bulk value of the lattice parameters. In addition, we find a depth behavior in the strain which is consistent with the formation of nonuniformly strained islands in the sample.

We report charge-ordered Bi0.4Ca0.6MnO3 thin films with charge-ordering temperature near room temperature, and observation of large photoinduced resistivity changes in these films associated with melting of the charge ordering by visible light. Films grown under small compressive strain exhibit the largest photoinduced resistivity changes. The lifetime of the photoinduced low-resistance state is on the order of half a minute. These photoinduced resistivity changes in thin films of Bi0.4Ca0.6MnO3 make them very promising for photonic device application.

We report our studies of the angular magnetic field dependence of the critical current density in epitaxial thin films of Nd 1.85 Ce 0.15 CuO 4−δ in the temperature range 1.4 K to 14 K. At low temperatures, the critical current anisotropy is well described by the 2D model of Josephson- coupled vortices. At temperatures above 10K, we observe deviations from the 2D behavior which may be attributed to the temperature dependence of the coherence length. The field dependence of the critical current density for the field orientation parallel to the CuO 2 planes is consistent with the dimensionality indicated by the angular dependence at all temperatures.

A careful analysis of high-resolution transmission electron microscopy images from La0.8Ca0.2MnO3 thin films indicates that the images can not explained based on either the classical Pnma structure or its monoclinic distortion. A cation ordered structure is proposed which could be responsible for the significantly higher Tc of the film (298K) compared with the bulk material of the same composition (190K).