SrRuO3 Thin Films Research Articles

Effect of Domain Structure on the Magnetoresistance of Epitaxial Thin Films of Ferromagnetic Metallic Oxide SrRuO3

ABSTRACTWe 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 Effect of Miscut Angle and Miscut Direction of Vicinal (001) SrTiO3 Substrates on The Domain Structure of Epitaxial SrRuO3 Thin Films

ABSTRACTWe have grown epitaxial thin films of isotropie metallic oxide SrRuC>3 on both exact and vicinal (001) SrTiO3 substrates with miscut angle (α) up to 5.0° and miscut direction (β) up to 37° away from the in-plane [010] axis. The effects of both α and β on the epitaxial growth and domain structure of epitaxial SrRuC>3 thin films were studied by x-ray diffraction and atomic force microscopy (AFM). On vicinal SrTiO3 substrates with a large miscut angle (α = 1.7°, 2.0°, 4.1°, and 5.0°) and miscut direction close to the [010] axis, single crystal epitaxial (110)° SrRuO3 thin films were obtained. [The superscript o refers to the Miller indices based on the orthorhombic unit cell.] Decreasing the substrate miscut angle or aligning the miscut direction close to the [110] axis (β = 45°) resulted in an increase of 90° domains in the plane. The films grown on vicinal substrates displayed a significant improvement in crystalline quality and in-plane epitaxial alignment as compared to the films grown on exact (001) SrTiO3 substrates. AFM revealed that as the miscut angle increased the growth mechanism changed from two dimensional nucleation to step flow growth.

The Effect of Elastic Strain on the Electrical and Magnetic Properties of Epitaxial Ferromagnetic SrRuO3 Thin Films

ABSTRACTWe report the direct measurement of elastic strain effect on the electrical and magnetic properties of single domain epitaxial SrRuO3 thin films, using a lift-off technique. The as-grown films on vicinal (001) SrTiO3 substrates are subjected to elastic biaxial compressive strain within the plane and tensile strain normal to the plane. In contrast, the lift-off films prepared by chemical etching of SrTiO3 substrates, are completely strain free with bulk like lattice. Our measurements indicate that the elastic strain can significantly affect the electrical and magnetic properties of epitaxial ferromagnetic SrRuO3 thin films. For the strained films, the Curie temperature (Tc) was suppressed to 150K and the saturation magnetic moment (Ms) was decreased to 1.15μB/Ru atom as compared to a Tc of 160K and Ms of 1.45μB/Ru atom for the strain free films. These property changes are attributed to the structural distortion due to the elastic strain in the as-grown epitaxial thin films. Our results provide direct evidence of the crucial role of lattice strain in determining the properties of the perovskite epitaxial thin films.

AFM Observations on the Growth Mechanisms of Epitaxial Perovskite Oxide SrRuO3 Thin Films

ABSTRACTThe growth mechanism and surface morphology of epitaxial SrRuO3 thin films deposited on exact and vicinal (001) SrTiO3 and exact (001) LaAlO3 substrates has been studied. Vicinal substrates with miscut angle, a, up to 4° toward [010] direction were used. Atomic force microscope images show that the films grown on exact (001) SrTiO3 substrate had a growth mechanism involving two dimensional nucleation. In contrast, characteristic step patterns were observed on the films deposited on vicinal substrates, suggesting that these films had a step flow growth mode. The films deposited on exact (001) LaAlO3 substrates had a three dimensional island growth, due to the incoherence between the film and substrate lattice. These results were found to be consistent with the results of x-ray diffraction analysis of the in-plane domain structure.

Domain Structures of Epitaxial SrRuO3 Thin Films

ABSTRACTThe structural characteristics of SrRuO3 thin films deposited on a (001) SrTiO3 substrate by pulsed laser were studied by transmission electron microscopy (TEM) and high-resolution TEM. TEM studies of cross-sectional specimens revealed the epitaxial growth of the films with the SrRuO3-(110) plane parallel to the SrTiO3-(001) plane. Two types of 90° rotational domain structures were observed in both cross-sectional and plan-viewing specimens. The in-plane orientations of these domains with respect to the substrate are either of SrRuO3-[110] // SrTiO3 - [100] and SrRuO3-[001] // SrTiO3-[010], or of SrRuO3-[110] // SrTiO3-[010] and SrRuO3-[001] // SrTiO3-[100].

SrRuO3 Thin Films Grown under Reduced Oxygen Pressure

SrRuO3 thin films are grown under reduced oxygen pressures between 10-6 Torr and 100 mTorr by pulsed laser deposition. The thin films grown at temperatures above 640° C and at a pressure of 10-6 Torr are characterized in terms of the lattice shrinkage due to oxygen deficiency. The resistivity increases and the temperature dependence changes to semiconductive from metallic as the oxygen pressure during growth is decreased. The Hall coefficient of the film grown at 740° C and at a pressure of 10-6 Torr is thirty times higher at low temperatures than at room temperature. The transport properties of the film are thought to result from the high carrier concentration but the low mobility due to the oxygen deficiency.

Microstructures and electrical properties of SrRuO3 thin films on LaAIO3 substrates

Conductive SrRuO{sub 3} thin films have been deposited using pulsed laser deposition. Structure and microstructure of this system were studied using XRD, SEM, and scanning tunneling microscopy. Electrical properties of these films were measured. The film deposited at 250{degree}C is amorphous-like, showing semiconductor-like temperature dependence of electric conductivity. Film deposited at 425{degree}C is crystalline with very fine grain size (100 {approximately} 200{angstrom}), showing both metallic and semiconductor-like temperature dependence of the electrical conductivity. Film deposited at 775{degree}C shows reisistivity of 280 {mu}{Omega}{center_dot}cm at RT and resisdual resistivity ratio of 8.4. Optimized deposition conditions were determined. Possible engineering applications of SrRuO{sub 3} thin films are discussed. Bulk and surface electronic structures of SrRuO{sub 3} are calculated using a semi-empirical valence electron linear combination of atomic orbitals, and they are used to understand the electrical properties of the films.

Characteristics of conductive SrRuO3 thin films with different microstructures

Conductive SrRuO3 thin films were epitaxially grown on (100) LaAlO3 substrates by pulsed laser deposition over a temperature range from 650 °C to 825 °C. Well-textured films exhibiting a strong orientation relationship to the underlying substrate could be obtained at a deposition temperature as low as 450 °C. The degree of crystallinity of the films improved with increasing deposition temperature as confirmed by x-ray diffraction, transmission electron microscopy, and scanning tunneling microscopy. Scanning electron microscopy revealed no particulates on the film surface. The resistivity of the SrRuO3 thin films was found to be a strong function of the crystallinity of the film and hence the substrate temperature during film deposition. A residual resistivity ratio (RRR = ρ300 K/ρ4.2 K) of more than 8 was obtained for the SrRuO3 thin films deposited under optimized processing conditions.

Structure and properties of heteroepitaxial Pb(Zr0.35Ti0.65)O3/SrRuO3multilayer thin films on SrTiO3(100) prepared by MOCVD and RF sputtering

Abstract 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)O3 (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 -19.7% volume fraction of 90° 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 Ω/cm2, a coercive field of 54.9 kV/cm, a dielectric constant of 410, a bipolar resistivity of ∼5.8x109 Ω-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 dependenc...

Properties Variation with Composition of Single-Crystal Pb(ZrxTi1−x,)O3 Thin Films Prepared by MOCVD

AbstractSingle-crystal thin films covering the full compositional range of Pb(ZrxTi1−x)O3(PZT) 0≤x≤1 have been deposited by metal-organic chemical vapor deposition (MOCVD). The films were grown on epitaxial, RF-sputter-deposited SrRuO3 thin film electrodes on (001) SrTiO3 substrates. X-ray diffraction (XRD), energy-dispersive electron spectroscopy (EDS) and optical waveguiding were used to characterize the crystalline structure, composition, refractive index, and film thickness of the deposited films. We found that the PZT films were single-crystalline for all compositions exhibiting cube-on-cube epitaxy with the substrate with very high degrees of crystallinity and orientation. We report the systematic variations in the optical, dielectric, polarization, and transport properties as a function of composition and the epitaxy-induced modifications in the solid-solution phase diagram of this system. These films exhibited electronic properties which showed clear systematic variations with composition. High values of remnant polarization (30–55 μC/cm2) were observed at all ferroelectric compositions. Unlike previous studies, the dielectric constant exhibited a clear dependence on composition with values ranging from 225–650. The coercive fields decreased with increasing Zr concentration to a minimum of 20 kV/cm at the (70/30) composition. In addition, these films exhibited both high resistivity and dielectric-breakdown strength (˜1013 Ω-cm at 100 kV/cm and >300 kV/cm, respectively) without any compensative doping.

Epitaxial Pb(Zr0.40Ti0.60)O3/SrRuO3 and PbTiO3/SrRuO3 Multilayer Thin Films Prepared by MOCVD and Rf Sputtering

ABSTRACTEpitaxial SrRuO3 thin films were deposited by RF sputtering on SrTiO3 or MgO substrates for use as underlying electrodes. On these conductive substrates, epitaxial Pb(Zr0.35Ti0.65)O3 (PZT) and PbTiO3 (PT) 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° domains, interfacial misfit dislocations and threading dislocations were the primary structural defects, and the films showed a 70% RBS channelling reduction. Hysteresis and dielectric measurements of epitaxial PZT ferroelectric capacitor structures formed using evaporated Ag or ITO glass top electrode showed: a remanent polarization of 46.2 μC/cm2 a coercive field of 54.9 kV/cm, a dielectric constant of 410, a bipolar resistivity of ∼5.8×109 ω-cm at a field of 275 kV/cm, and a breakdown strength of >400 kV/cm.

Properties of epitaxial SrRuO3 thin films

SrRuO3 thin films were deposited on (100) LaAlO3 using pulsed laser deposition. The films were (001) oriented normal to the substrate surface with a high degree of in-plane orientation with respect to the substrate’s major axes. An ion beam minimum yield of 2.5% was obtained for the films, indicating high crystallinity. The films exhibited metallic behavior with a room temperature resistivity of ∼200 mW cm. A kink in the resistivity, corresponding to a ferromagnetic phase transition, was observed at ∼160 K. It was found that SrRuO3 is structurally and chemically compatible with the YaB2Cu3O7−d (YBCO) superconductors. High quality YBCO films were obtained on SrRuO3 LaAlO3. Multilayers of YBCO/SrRuO3 were successfully fabricated.