Bulk, single crystal, and metal-organic chemical-vapor deposition thin-film samples of Gd0.67Ca0.33MnO3 were prepared and examined for their electrical, magnetic, and structural properties. Gd0.67Ca0.33MnO3 is ferrimagnetic with a transition temperature between 50 and 80 K and a compensation temperature of about 15 K. A molecular field model with a ferromagnetic manganese sublattice antiparallel to the gadolinium sublattice qualitatively explains the magnetism data. A large high-held susceptibility is observed at 5 K, suggesting a sublattice rotation. The resistivity and the magnetoresistance show no anomaly near the ferrimagnetic transition. There is no noticeable change in the structure, as seen from the x-ray-absorption fine structure between 40 and 69 K, indicating that there is no structural discontinuity across the paramagnetic insulator to ferromagnetic insulator phase boundary. The resistivity of Gd0.67Ca0.33MnO3 is consistent with small polaron hopping at high temperatures (up to 1100 K), and possibly by a different mechanism at low temperatures.

Abstract— Thin ZnS:Mn and SrS:Ce electroluminescent films are grown by solid‐source metal‐organic chemical vapor deposition (MOCVD). The method is attractive because it uses relatively non‐toxic materials and does not require flammable hydrogen or toxic H2S. Performance results are presented for both blue‐ and white‐emitting phosphors. Even though the method has not yet been optimized, luminous efficacy of 3 lm/W at low drive voltages has been attained for ZnS: Mn.

An investigation designed to display the intrinsic properties of perovskite manganites was accomplished by comparing the behavior of bulk samples with that of thin films. Epitaxial 1500 \AA{} films of perovskite ${\mathrm{La}}_{0.67}$${\mathrm{Ca}}_{0.33}$Mn${\mathrm{O}}_{3}$ and ${\mathrm{La}}_{0.67}$${\mathrm{Sr}}_{0.33}$Mn${\mathrm{O}}_{3}$ were grown by solid source chemical vapor deposition on LaAl${\mathrm{O}}_{3}$ and post annealed in oxygen at 950 \ifmmode^\circ\else\textdegree\fi{}C. Crystals were prepared by laser heated pedestal growth. The magnetic and electrical transport properties of the polycrystalline pellets, crystals, and annealed films are essentially the same. Below $\frac{{T}_{C}}{2}$ the intrinsic magnetization decreases as ${T}^{2}$ (as can be expected for itinerant electron ferromagnets) while the intrinsic resistivity increases proportional to ${T}^{2}$. The constant and ${T}^{2}$ coefficients of the resistivity are largely independent of magnetic field and alkaline earth element (Ca, Sr, or Ba). Hall effect measurements indicate that holes are mobile carriers in the metallic state. We identify three distinct types of negative magnetoresistance. The largest effect, observed near the Curie temperature, is 25% for the Sr and 250% [$\frac{\ensuremath{\Delta}R}{R(H)}$] for the Ca compound. There is also magnetoresistance associated with the net magnetization of polycrystalline samples which is not seen in films. Finally a small magnetoresistance linear in $H$ is observed even at low temperatures. The high temperature (above ${T}_{C}$) resistivity of ${\mathrm{La}}_{0.67}$${\mathrm{Ca}}_{0.33}$Mn${\mathrm{O}}_{3}$ is consistent with small polaron hopping conductivity with a slight transition at 750 K, while ${\mathrm{La}}_{0.67}$${\mathrm{Sr}}_{0.33}$Mn${\mathrm{O}}_{3}$ does not exhibit activated conductivity until about 500 K, well above ${T}_{C}$. The limiting low and high temperature resistivities place a limit on the maximum possible magnetoresistance of these materials and may explain why the "colossal" magnetoresistance reported in the literature correlates with the suppression of ${T}_{C}$.

The observed H2 and |H| dependence of the magnetoresistance above and below TC, respectively, may be explained by general time-reversal symmetry considerations. We further find empirically that the saturation observed in the magnetoresistance is best fit by a simple resistor in series with a magnetoconductor: ρ(H)=ρ∞+1/(σ0+γ|H|) for TTC. This provides a functional form to analyze and predict the magnetoresistance over a wide range of fields. This suggests that the underlying mechanism of ‘‘colossal magnetoresistance ’’ may be magnetoconductive, not magnetoresistive. The magnetoresistance and Hall effects on an annealed epitaxial thin films of La0.67Ca0.33MnO3 were measured at 0.9 TC and 1.1 TC. At low fields, anisotropic magnetoresistance plays a dominant role. The high field Hall effect shows holelike carriers above and below TC. The apparent change in sign at low fields is likely due to the anomalous Hall effect.

Resistivity measurements on a La0.67Ca0.33MnO3 film are reported for a series of argon anneals at successively higher temperatures. T-c, the ferromagnetic ordering temperature, increases uniformly with increasing annealing temperature and annealing time. Hence, T-c can be tuned by appropriate annealing. In order to fully anneal these samples, i.e., achieve bulk properties, it proves sufficient to anneal them in argon. Further annealing in oxygen produces only minor changes in the resistivity. Data from T-c up to 1200 K show activated conduction with rho = BTeEa/kT, the temperature dependence predicted by the Emin-Holstein theory of adiabatic polaron hopping. Their model fits both data from the partially annealed and fully annealed samples better than the variable range hopping or semiconductor models which have been used by previous workers. The activation energy E(a) and resistivity coefficient B decrease with increasing maximum anneal temperature. These changes, together with the increase in T-c, are consistent with an anneal induced relaxation of the Mn-O-Mn bond angle. The time dependent resistivity during annealing at a fixed temperature follows the equation rho=rho(0){1-D ln[1+(t-t(0))/tau]}, making it possible to acquire data in a reversible regime, and also to obtain an estimate of the annealing activation energy. (C) 1996 American Institute of Physics.

An investigation designed to display the intrinsic properties of perovskite manganites was accomplished by comparing the behavior of bulk samples with that of thin films; the results show the "colossal magneto resistance" at very low temperatures is not an intrinsic property of the thermodynamically stable 1/3 doped material. Epitaxial 1500 Å films of perovskite La0.67Ca0.33MnO3 and La0.67Sr0.33MnO3 were grown by solid source chemical vapor deposition on LaA1O3 and post annealed in oxygen at 950°C. Crystals were prepared by LASER heated pedestal growth. The magnetic and electrical transport properties are essentially the same. Below Tc/2 the intrinsic magnetization decreases as T2 (as can be expected for itinerant electron ferromagnets) while the intrinsic resistivity increases proportional to T2. The constant and T2 coefficients of the resistivity are largely independent of magnetic field and alkaline earth element (Ca, Sr or Ba). We identify three distinct types of negative magnetoresistance. The largest effect is observed near the Curie temperature and is likely to be due to magnetic critical scattering. There is also magnetoresistance associated with the net magnetization of polycrystalline samples. The high temperature (above Tc) resistivity of La0.67Ca0.33MnO3 is consistent with small polaron hopping conductivity with a transition at 750K, while La0.67Sr0.33MnO3 does not exhibit activated conductivity until about 500K, well above Tc. The limiting low and high temperature resistivities may place a limit on the maximum possible magnetoresistance of these materials.

C-axis LiNbO3 epitaxial films have been grown on c-plane sapphire substrates by solid source metal-organic chemical vapor deposition (MOCVD) using the tetramethylheptanedionate sources, Li(thd) and Nb(thd)4. Stoichiometric LiNbO3 films were deposited from Li(thd)-rich source compositions. Rocking curve FWHM values as low as 0.044°were measured on films grown at 710 °C. Rocking curve peak widths became broader as films were grown at progressively lower substrate temperatures. Single prism coupling experiments revealed clearly visible optical waveguiding, with optical attenuation values as low as 2 dB/cm in the best films.

By the solid source MOCVD technique, we have deposited 2000 - 3000 Å thick single phase SrxBa1−xNb2O6 (SBN) films on (100) MgO substrates using tetramethylheptanedionate (thd) sources. X-ray diffraction (XRD) 2θ scans indicated that these films were completely (001) oriented. XRD Φ scans, however, showed the films contained four in-plane grain orientations whose volume fractions could be controlled by altering the Sr/(Sr+Ba) and Nb/(Sr+Ba) ratios in the source powders. The in-plane volume fractions did not change with the deposition rate or the cooling rate. Films with composition Sr0 58Ba0.42Nb1.94O6 had mainly two in-plane orientations. Optical waveguiding behavior was demonstrated in these films. Refractive indices were found to be no= 2.20 and ne = 2.13, as compared to no = 2.31 and ne = 2.27 for bulk SBN60.

The solid source MOCVD technique1,2, employing a single powder vaporization source composed of mixed beta-diketonate metalorganic compounds, has been used to grow thin films of a variety of electro-optic materials, including lithium niobate, strontium barium niobate, and potassium niobate. Results for potassium niobate films are quite preliminary, but indicate that a volatile potassium organometallic source can be synthesized which is useful for growing potassium niobate by MOCVD. High quality single phase (001) oriented strontium barium niobate films have been deposited which exhibit waveguiding behavior. The most extensive work has been done on lithium niobate, which has been deposited epitaxially on a variety of substrates. Oriented z-axis (001) films have been grown on c-axis sapphire with and without a (111) oriented platinum base electrode and on a bulk grown lithium niobate substrate. Films grown directly on c-axis sapphire at 700 C exhibit x-ray rocking curve linewidths as low as.044 degrees, nearly perfect in-plane orientation as determined by x-ray phi scans, and peak-to-peak surface roughness less than 40 Å. Optical waveguiding has been demonstrated by a single prism coupling technique on similar films 1175 - 2000 Å thick grown at 500 C, with optical losses of approximately 2 db/cm at 632.8 nm measured over 3.5 cm long films. Polarization vs. electric field measurements on 1100 Å thick films grown on platinum show a hysteresis loop indicating ferroelectric behavior.

In this paper, we introduce a method which makes it possible to rapidly and accurately determine the penetration depth as a function of temperature for superconductive thin film samples. A key feature of the approach described here is that it is derived only from electrodynamic definitions and makes no use of a selected model of superconductivity. Another advantage relative to some of the alternative methods presently in use is that it can be expected to give useful results for films with thicknesses that are as much as three times the zerotemperature effective penetration depth. When combined with an accurate evaluation ofR S as a function of temperature for the same samples, these penetration depth data enable the computation of the complex conductivity for a wide variety of samples. One shortcoming of the method is the fact that it performs well only at temperatures below about 0.95Tc.