A variety of plasma etching chemistries were examined for patterning NiMnSb Heusler thin films and associated A12O3 barrier layers. Chemistries based on SF6 and Cl2 were all found to provide faster etch rates than pure Ar sputtering. In all cases the etch rates were strongly dependent on both the ion flux and ion energy. Selectivities of ≥20 for NiMnSb over A12O3 were obtained in SF6-based discharges, while selectivities ≤5 were typical in Cl2 and CH4/H2 plasma chemistries. Wet etch solutions of HF/H2O and HNO3/H2SO4/H2O were found to provide reaction-limited etching of NiMnSb that was either non-selective or selective, respectively, to A12O3. In addition we have developed dry etch processes based on Cl2/Ar at high ion densities for patterning of LaCaMnO3 (and SmCo permanent magnet biasing films) for magnetic sensor devices. Highly anisotropie features are produced in both materials, with smooth surface morphologies. In all cases, SiO2 or other dielectric materials must be used for masking since photoresist does not retain its geometrical integrity upon exposure to the high ion density plasma.

Thin films of La1-xSrxMnO3 (x=0.4) were fabricated using pulsed laser deposition (PLD) methods. The surface morphology of the films was sensitively affected by oxygen pressure during deposition. At high oxygen pressure (∑150 mTorr), randomly aligned grains were nucleated on the epitaxial film. When the pressure was reduced to 100 mTorr, the epitaxial film had very smooth surface. Under this condition, the thickness dependence of resistivity and magnetization were analyzed. Even 6 nm thick film showed ferromagnetic metallic behavior. The AFM images of ulta thin films deposited on wet-etched SrTiO3 showed atomically flat terraces and 0.4 nm steps. The film growth mode can be tuned to either layer by layer or step flow by the deposition temperature.

Thin-film samples of La1-xSrxMnO3 (x = 0.20 – 0.30) were grown by pulsed-laser deposition using various target compositions, substrate materials, growth temperatures, oxygen partial pressures, and laser-pulse repetition rates. The crystal structure and the transport and magnetic properties of these films were then examined. Of the growth conditions, the oxygen partial pressure (Po2) had the greatest influence on the electrical and magnetic properties. Films grown under a low Po2 had a low ferromagnetic transition temperature (Tc) and a wide resistive transition width. None of the heat treatments done after growth improved these films’ quality. The film morphology was significantly affected by the substrate material. Our x-ray diffraction analysis and AFM measurements revealed that the films deposited on both MgO (100) and LaAlO3 (100) were epitaxially grown but contained defect structures. In contrast, grain-free thin films were epitaxially grown on the SrTiO3 (100) substrates. The surface roughness of films grown on SrTiO3 was less than 0.3 nm, even for films up to 150 nm thick. Under optimized growth conditions, as-deposited films for x ≥ 0.2 showed a sharp transition in resistivity at Tc. Magnetoresistance at far below Tc was as low as that reported for single-crystal sample. Since large magnetoresistance was often observed in polycrystalline samples and believed to be a grain boundary effect, these results indicate the high quality of the films grown on the SrTiO3 substrates.

Thin films of calcium doped lanthanum manganites Lal-xCaxMnO3 (LCMO) with x ∼ 0.41 have been prepared on LaAlO3(001) (LAO) Y-stablized ZrO2(001) (YSZ), and Al2O3(0001) (SAP) substrates by liquid delivery metal-organic chemical vapor deposition (LD-MOCVD). The films on YSZ and SAP substrates have a textured, polycrystalline morphology with a preferred orientation of (110). The films on LAO show a single-crystalline morphology and a (100) orientation. Transport measurements show the polycrystalline films have a resistance peak approximately 60K lower than the films on LAO and, in general, have a much higher overall resistance. The magne-toresistance (MR) ratio ([R(H) - R(0)]/R(H)) is sharply peaked near the maximum in resistance for the films on LAO, while the polycrystalline films show a noticeable absence of this sharply peaked behavior and a flat, rather large (∼ 100%) MR ratio over a large temperature range. These results will be discussed in terms of grain boundary scattering, crystallite size, and magnetization.

Densification behavior and microstructural characteristics of nanocrystalline LiZn ferrites with chemically derived additives were investigated. Nanocrystalline Li0.3Zn0.4Fe2.3O4 powders having a ≈ 15 nm size were prepared at a low temperature of 450°C by a chemical synthesis using a combustible polyacrylic acid (PAA). Small amounts of Si, Ca and Mn were incorporated into the nanocrystalline ferrites via sol-gel reactions utilizing tetraethyl orthosilicate, calcium isopropoxide and manganese acetate. This process was believed to give a homogeneous distribution of the additives over the nanocrystalline ferrites. A uniform microstructure was obtained without any evidence of exaggerated grain growth after sintering at 1100°C. Saturation magnetization and coercive force were found to increase with the chemical additives. The results were compared with those of the same composition, but processed by the conventional batch-mixing of corresponding oxide additives.

The crystal structure and magnetic properties in epitaxially grown Sr1-xBaxRuO3 on SrTiO3 substrates were determined. Epitaxial Sr1-xBaxRuO3 exhibits a simple perovskite structure in the whole region of Ba/Sr ratio, in contrast to a complex hexagonal layered perovskite in the case of Ba-rich bulk Sr1-xBaxRuO3 which has plane-sharing oxygen octahedra. Tetragonal deformation was enhanced from the pseudo cubic structure of SrRuO3 to a highly distorted tetragonal lattice in BaRu03. Electronic properties such as conductivity and magnetization were examined and compared to the results of band calculation in which a tetragonal distortion was taken into account. A metal-insulator transition was not observed in this system either in the experiment or in the simulation, and metallic conductivity was maintained in the whole region of Ba content. The ferromagnetic ordering which occurs at 160K in pseudo-cubic bulk SrRuO3 was suppressed in Sr1-xBaxRuO3 films with increasing tetragonal deformation and Curie temperature decreased to 50K in BaRuO3.

We have investigated the magnetic anisotropies of doped manganite materials in epitaxial thin film and single crystal form. Structural characterization, including x-ray diffraction, Rudierford backscattering spectroscopy and atomic force misocroscopy, indicate that our epitaxial films arc single crystalline and have excellent crystallinity. Since lattice distortions greatly affect the magnetic and transport properties of this family of materials, it is not surprising to find the profound effect of strain in films due to the lattice mismatch between the substrate and film. Magnetic anisotropy results of single crystals, subject to no external stress, is compared to those of epitaxial films.

The changes with temperature in the crystallographic structure of the two-layered La1.4Sr1.6Mn2O7, are on average quite small but the atomic pair density function analysis of pulsed neutron diffraction data shows that the lattice is locally distorted in accordance with the change in the transport properties. In particular, while no Jahn-Teller (JT) distortion is expected in the layered compounds because the octahedral bilayers are almost cubic, lattice distortions attributed to a large JT effect are present and are of comparable magnitude as in the cubic perovskite system. This could in turn explain the similarity in their properties. The number of the JT distorted sites is reduced with temperature concomitantly with the decrease in resistivity of the ab-plane.

Systematic Mn K-edge x-ray absorption spectroscopy (XAS) measurements on samples of La1-xSrxMnO3, which are precursors to colossal magnetoresistive (CMR) materials, are reported. Detailed results on the edge or chemical shift as a function of Sr concentration (hole doping) and sample preparation (air vs oxygen annealed), are discussed. For comparison, a systematic XANES study of the Mn K-edge energy shift, denoting valence change in Mn, has been made in standard manganese oxide systems. Contrary to expectations, the variation in near-edge energies for Mn in La0.725Sr0.275MnO3 were small when compared to the difference between that for manganese oxide standards of nominal valence of +3 and +4 (Mn2O3 and MnO2).

In this work we report a study of the photoinduced insulator-to-metal transition in manganese oxide perovskites of the formula Pr1-xCaxMnO3. The transition is closely related to the magnetic field induced insulator-to-metal transition (CMR effect) observed in these materials. It is accompanied by a dramatic change in the magnetic properties and lattice structure: the material changes from an insulating charge-ordered canted antiferromagnet to a ferromagnetic metal. We present an investigation of the transport and structural properties of these materials over the course of the transition (which usually takes about an hour to complete). The current-voltage characteristics exhibited by the material during the transition are highly nonlinear, indicating a large inhomogeneity of the transitional state. Possible practical applications of this novel type of transition are briefly discussed. We also report a high-resolution x-ray diffraction study of the charge-ordering in these materials. The temperature dependent charge ordering structure observed in these compounds is more complex than previously reported.

We have studied resonant V Lα-fluorescence spectra of vanadium oxides with V in several different oxidation states. The spectra are dominated by the O 2p-contribution centered at about 6 eV below the top of the valence band (VB-top). The V 3d-contribution, found close to the VB-top, increases with decreasing valency of the vanadium atoms. Resonant inelastic (Raman) x-ray scattering is fairly weak in these compounds and overlaps with the ordinary fluorescence spectrum. Large spectral changes of V Lα-fluorescence in the metal-insulator transition of V2O3 have been observed.

We have investigated electronic transport and magnetic properties of perovskite-type Nd1-xSrxMnO3 crystals with change of controlled hole-doping level (0.30≤x≤0.80). The electronic phase diagram of Nd1-xSrxMnO3 was obtained by systematic measurements of magnetization (magnetic structure), resistivity, and lattice parameter. We have also studied the anisotropie transport properties of x=0.50 and 0.55 crystals with different magnetic structures: CE-type antiferromagnetic (AF) structure for x=0.50 and A-type layered AF one for x=0.55. In the case of the x=0.55 crystal, the metallic behavior was observed within the ferromagnetic (F) layers, while along the AF-coupling direction the crystal remains insulating over the whole temperature region. The observed large anisotropy is due to the magnetic as well as orbital-ordering induced confinement of the spin-polarized carriers within the F sheets. The nearly isotropie transport behavior has been confirmed for the CE-type AF charge-ordered state in the x=0.50 crystal.

The stoichiometry, structural and magnetic properties, and Mössbauer spectra of reactively sputtered Fe-O films were studied as a function of the O2 partial pressure during the deposition. By increasing the amount of O2 films with the following crystallographic structures and stoichiometry were fabricated; amorphous Fe-O, mixture of Fe and FeO, offstoichiometric single-phase FexO, mixture of FeO and Fe3O4, single-phase Fe3O4, mixture of Fe3O4 and γ-Fe2O3, mixture of Fe3O4 and α-Fe2O3, and single-phase α-Fe2O3. The Verwey transition in Fe3O4 films was observed in the coercivity versus temperature curve and in the thermomagnetic data. FeO and α-Fe2O3 films showed anomalous ferromagnetic-like behavior, in contrast to their anti ferromagnetic nature in bulk. The unusual magnetic properties were attributed to the formation of clusters of tetrahedraly coordinated Fe3+ ions in FeO and to uncompensated surface spins, in α - Fe2O3 films.

Measurements and analysis of the paramagnetic susceptibility of La1-xCaxMnO3+y (0 ≤ x ≤ 1) are reported. The magnetization was also measured in large fields (H ≤ 18 tesla) for a specimen of La0.79Ca0.21MnO3+y. The paramagnetic susceptibility is observed to be strongly enhanced for most compositions studied, including a number of antiferromagnetic compositions. This behavior is attributed to the existence of magnetic polarons.

We have grown epitaxial ferromagnetic metallic oxide SrRuO3 thin films with different domain structures on (001) LaAlO3 and miscut (001) SrTiO3 substrates. The effect of crystallographic domain structures on the magnetization and magnetoresistive behavior of epitaxial SrRuO3 thin films has been studied. Magnetization measurements on the single domain film on 2° miscut (001) SrTiO3 substrate showed that the in-plane [110] direction, which is aligned along the miscut direction, is the easier axis for magnetization compared to the [001] direction. This film also showed a strong anisotropie magnetoresistance (AMR) effect of ∼ 8% in magnitude. In contrast, the SrRuO3 thin film on (001) LaAlO3 substrate shows identical magnetization and magnetoresistance behavior in two orthogonal directions on the film due to the presence of 90 domains in the plane. For both the films, large negative magnetoresistance effects (-10%) were observed when the current and the applied magnetic field are parallel. The magnetoresistance behavior is explained in terms of suppression of spin fluctuations near Tc and the AMR effect.

The pair density function (PDF) used in the analysis of pulsed neutron diffraction data of La1-xSrxCoO3 revealed new structural effects which are correlated to the susceptibility and transport transitions. The transition in the spin configuration of the Co ions from the low-spin (LS) to the high-spin (HS) state in the Co perovskite oxides can potentially induce structural distortions due to the coupling of the spin to the lattice and charge. The ground state of the pure compound, LaCoO3, is in the LS state and is non-magnetic. A transition occurs to the HS state at ∼ 50 K as indicated from the susceptibility measurements due to the thermal excitation of electrons to the eg level. The CoLSO6 octahedra associated with the Co ions in the LS configuration are distinguished from the CoHSO6 octahedra with the Co in the HS configuration because the CoLS-O bond length is shorter than the CoHS-O distance due to the different size of the corresponding Co ions. Such bond lengths are clearly identified in the local structure between 15 – 300 K. This finding is in contrast to the average structure which shows only one type of bond length in this temperature range but two types of bond lengths are suggested at considerably higher temperatures. This suggests that whereas the LS and HS CoO6-octahedra coexist, they are randomly distributed in the crystal lattice at lower temperatures and become ordered at higher temperatures. The introduction of charge carriers in the structure does not eliminate the coexistence of both the LS and HS states, indicating that with the transition to the ferromagnetic metallic state, the spin configuration is not entirely of the HS character and structural inhomogeneities are present.

Magnetic oxides of (La,A)MnO3 and (La,A)CoO3 have two typical structural characteristics: cations with mixed valences and oxygen vacancies, which are required to balance the charge introduced by cation doping. The consequences introduced by each can be different, resulting in different properties. It is important to quantitatively determine the percentage of charges balanced by each, but this analysis is rather difficult particularly for thin films. This paper has demonstrated that electron energy-loss spectroscopy (EELS) can be an effective technique for analyzing Mn and Co magnetic oxides with the use of intensity ratio of white lines, leading to a new technique for quantifying oxygen vacancies in functional and smart materials.

Transport and magnetic properties of layered cobalt oxide (BiPb)2Sr3Co2O9 are investigated in detail under magnetic field up to 8 T. Parent compound, Bi2Sr3Co2O9, is a typical band insulator with Co ions being in a low-spin 3+ state because of the well-separated dε and dγ levels possibly due to a strong crystal field. We have tried to introduce holes mainly by Pb substitution for Bi. The hole-doped sample shows metallic behavior in a resistivity measurement between 300 and 30 K. Below 30 K, however, the resisitivity increases. Under the magnetic field the resistivity is strongly suppressed in this region. We observed more than 30% resistivity drop at 2 K under H = 8 T, which is comparable to insulating (La,Sr)CoO3 system. We discuss the mechanism of hole doping and the origin of negative magnetoresistance with tranport and magnetic properties, and point out that the conventional double-exchange mechanism cannot be applied to this system. This means that some new mechanism is necessary to explain this phenomenon.

Y3Fe5O12(YIG) and La-doped YIG films were grown on the {111} GGG substrate using the PbO-B2O3 flux system. Pb, La incorporation and lattice misfit and annealing behaviors were studied. In the case of LPE growth of YIG film, lead ions from flux are substituted inevitably, and they play an important role in controlling film misfit. For a complete lattice matching, high supercooling is necessary in pure YIG growth, but this induces high defect concentration. In this experiment, La ions were added in the solution to sufficiently increase lattice parameter of the film grown under low supercooling. The concentration of substituted Pb and La were increased as the growth temperature was lowered and growth rate increased. The effective distribution coefficient of La was about 0.2 at a supercooling of 30 °C. The optimum growth conditions which bring about very small misfit were determined by measuring the misfit by double crystal diffractometer. Strain distributions of pre-annealed and annealed samples were investigated by triple crystal diffractometer.

With a use of the epitaxial a-axis thin films of perovskite series Lan-nxCa1+nxMnnO3n+1 (n=2,3, and ∞) with fixed carrier concentration (x=0.3), the transport properties of the series compounds have been examined to be associated with the difference in the number of the MnO2 layers. Results have indicated that a reduction in the number of layers results in systematic changes in the various features. These include an increase in resistivity, a decrease in resistivity peak temperature Tcρ corresponding to the metal-insulator transition, an enhancement of the maximum MR near Tcρ, and an increase in low temperature intrinsic MR. In order to explain the variation in these features with the number of MnO2 layers, it is necessary to take both anisotropie c-axis transfer interaction and two-dimensional spin fluctuation into account.