A La0.7Ca0.3MnO3 thin film made by pulsed laser deposition (PLD) and another film of the same composition made by metal organic chemical vapor deposition (MOCVD), both on single crystal LaAlO3, were subject to a series of six, short, controlled anneals. The oxygen content was purposely not changed in the films from the first anneal to subsequent anneals. After each anneal, the film microstructures were characterized to determine average grain size, lattice constants, nonuniform strain, and crystalline mosaic spread, and these parameters were correlated with the magnetotransport properties. For both sets of films, the influence of annealing was to both increase the temperature at which the maximum in the magnetoresistance occurs (Tm) and the maximum magnetoresistance (MR) value. The improvement in film properties occurred in conjunction with stress relaxation and improved crystallinity, as a result of grain growth. The MOCVD films showed poorer grain coupling and poorer epitaxy compared to the PLD films. These features did not significantly influence the absolute values of the resistivity, but did produce spin canting in the MOCVD film, as seen in magnetization and resistivity versus field data. The canting resulted in a lower Tm and depressed MR value for the MOCVD film which increased only marginally with annealing. The work highlights the importance of controlling microstructure for optimizing properties of colossal magnetoresistance films.

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.

Ferroelectric thin films as the recording media of scanning probe microscope based storage devices were investigated using an atomic force microscope(AFM) technique. Polarization domains were formed in the PbZrxTi1-xO3(PZT) thin films epitaxialy grown on the epitaxial SrRuO3(SRO) thin films on SrTiO3 substrate by applying a pulse voltage between the conductive tip of AFM and SRO as a bottom electrode. The polarized domains were observed by detecting the inverse-piezoelectricity-induced surface vibration of the PZT thin film caused by applying an ac modulation voltage to the conductive tip. The recording density of polarized domains, domain switching speed and preliminary retention characteristics of polarized domains were studied. The polarized domains as small as 30 nn are formed in the PZT thin film with the thickness of 45 nm. The small domains can be formed by applying a 100 us pulse of 10 V to the conductive tip. As for the retention characteristics of polarized domains with a size of 90-110 nm, the temperature dependence of domain retention time was found to be in accordance with the Arrhenius model. Extrapolation of the Arrhenius plot leads to an estimation that the time for 50% of polarized domains to become smaller than half initial size at 50 degrees C is 34 years for 90-110 nm polarized domains in the 45 nm PZT thin film.

Bulk, single crystal, and metal-organic chemical-vapor deposition thin-film samples of ${\mathrm{Gd}}_{0.67}$ ${\mathrm{Ca}}_{0.33}$ ${\mathrm{MnO}}_{3}$ were prepared and examined for their electrical, magnetic, and structural properties. ${\mathrm{Gd}}_{0.67}$ ${\mathrm{Ca}}_{0.33}$ ${\mathrm{MnO}}_{3}$ 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-field 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 ${\mathrm{Gd}}_{0.67}$ ${\mathrm{Ca}}_{0.33}$ ${\mathrm{MnO}}_{3}$ is consistent with small polaron hopping at high temperatures (up to 1100 K), and possibly by a different mechanism at low temperatures.

Nanometer size polarized domains were written in a PbZr1−xTixO3 (PZT) thin film using an atomic force microscope (AFM) and the relationship between the polarized domain and the grain of the film was investigated. The polarized domain was formed by applying a pulse voltage to the ferroelectric PZT thin film through a conductive AFM tip. The polarized domain structure was observed by imaging the piezoelectric-induced surface vibration by an AFM with an ac voltage applied between the tip and the bottom electrode of a sample. The polarized domains with a diameter of 50 nm were written within a single grain.

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 critical magnetic properties of bulk La0.67Ca0.3MnO3 and magnetoresistance of a thin film with the sameTc were measured and critical exponents determined. The magnetization data can be scaled with β = 0.3 and γ = 0.9, except aboveTc which appears to be affected by a region whereX3 (M =XH +X3H3) is positive. AnM2 dependence of the magnetoconducitvity is observed aboveTc. BelowTc, however, such a correspondence between the critical magnetic and transport behavior is not found.

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.

Epitaxial SrRuO3 thin films were deposited on SrTiO3(100) substrates by RF sputtering for use as bottom electrodes and epitaxial buffer layers. On these conductive substrates epitaxial Pb(Zr0.35Ti0.65)O-3 (PZT) thin films were deposited by metalorganic chemical vapor deposition (MOCVD). X-ray diffraction (XRD), transmission electron microscopy (TEM) and optical waveguiding were used to characterize the phase, refractive index, and film thickness of the deposited films. The epitaxial PZT films were c-axis oriented and contained similar to 19.7% volume fraction of 90 degrees domains. Ferroelectric hysteresis and dielectric measurements of epitaxial PZT ferroelectric capacitor structures formed using sputtered ITO top electrodes showed: a remanent polarization of 51.8 mu C/cm(2), a coercive field of 54.9 kV/cm, a dielectric constant of 410, a bipolar resistivity of similar to 5.8x10(9) Omega-cm at a field of 275 kV/cm, and a breakdown strength of >400 kV/cm. The cyclic fatigue behavior of the films showed a strong dependence on the choice of electrode materials and the fatiguing wave form. These data support the model that the fatigue mechanism in these films arises from the trapping of injected charge carriers and is predominately an electronic phenomenon.

Epitaxial SrRuO3 thin films were deposited on SrTiO3(100) and MgO(100) substrates by rf sputtering for use as bottom electrodes and epitaxial buffer layers. On these conductive substrates, epitaxial Pb(ZrxTi1-x)O3 (PZT; x equals 0.35, 0.65) and PbTiO3 (PT; x equals 0) thin films were deposited by metalorganic chemical vapor deposition (MOCVD). X-ray diffraction (XRD), RBS channeling (RBS), transmission electron microscopy (TEM) and optical waveguiding were used to characterize the phase, microstructure, defect structure, refractive index, and film thickness of the deposited films. The PZT and PT films were epitaxial and c-axis oriented. Ninety degree domains, interfacial misfit dislocations and threading dislocations were the primary structural defects, and the films showed as high as 70% RBS channeling reduction. Ferroelectric hysteresis and dielectric measurements of epitaxial PZT ferroelectric capacitor structures formed using evaporated Ag top electrode showed: a remanent polarization of 46.2 (mu) C/cm2, a coercive field of 54.9 kV/cm, a dielectric constant of 410, a bipolar resistivity of approximately 5.8 X 109 (Omega) -cm at a field of 275 kV/cm, and a breakdown strength of > 400 kV/cm. Cyclic fatigue measurements showed that the remanent polarization was maintained for > 109 cycles.

Epitaxial SrRuO{sub 3} thin films were deposited on SrTiO{sub 3}(100) and MgO(100) substrates by RF sputtering for use as bottom electrodes and epitaxial buffer layers. On these conductive substrates, epitaxial Pb(Zr{sub x}Ti{sub 1{minus}x})O{sub 3} (PZT; x = 0.35,0.65) and PbTiO{sub 3} (PT; x = 0) thin films were deposited by metalorganic chemical vapor deposition (MOCVD). X-ray diffraction (XRD), RBS channeling (RBS), transmission electron microscopy (TEM) and optical waveguiding were used to characterize the phase, microstructure, defect structure, refractive index, and film thickness of the deposited films. The PZT and PT films were epitaxial and c-axis oriented. 90{degree} domains, interfacial misfit dislocations and threading dislocations were the primary structural defects, and the films showed as high as a 70% RBS channeling reduction. Ferroelectric hysteresis and dielectric measurements of epitaxial PZT ferroelectric capacitor structures formed using evaporated Ag top electrode showed: a remanent polarization of 46.2 {mu}C/cm{sup 2}, a coercive field of 54.9 kV/cm, a dielectric constant of 410, a bipolar resistivity of {approximately}5.8 {times} 10{sup 9} {Omega}-cm at a field of 275 kV/cm, and a breakdown strength of >400 kV/cm. Cyclic fatigue measurements showed that the remanent polarization was maintained for >10{sup 9} cycles.