Wenbin Wu

Field-induced crossover from cluster-glass to ferromagnetic state in La0.7Sr0.3Mn0.7Co0.3O3

The thermodynamics and kinetics of the magnetic states of the semiconductor-like compound La0.7Sr0.3Mn0.7Co0.3O3 were studied by detailed magnetic measurements. The spontaneous magnetic state was found to be a cluster-glass phase which can cross over to a ferromagnetic state under an external magnetic field H. The defreezing temperature Tf for the cluster-glass phase and the merging temperature Tm for zero field cooled and field cooled magnetizations are related to the field H by Hj=H0j(1−Tj/Tc)nj, where H0j and nj are constants and j=f,m. Codoping tends to destroy the double exchange in Mn4+–O–Mn3+ and broadens the coexistence region of the cluster-glass and ferromagnetic states. The magnetic relaxation was found to deviate from the usual logarithmic time dependence and follow a power law.

Energy band alignment between Pb(Zr,Ti)O3 and high and low work function conducting oxides—from hole to electron injection

The interface formation between Pb(Zr,Ti)O3 (PZT) and RuO2 and between PZT and In2O3u2009:u2009Sn (ITO), respectively, was characterized using in situ x-ray photoelectron spectroscopy (XPS). No interface reaction was observed for the interfaces studied. The Fermi level position at the interface (Schottky barrier height) is strongly different for the two electrode materials. A Fermi level position of 1.0 ± 0.1u2009eV above the valence band maximum (VBM) is observed for the contact between PZT and the high work function oxide RuO2. For the contact between PZT and the low work function oxide ITO a Fermi level position of 2.1 ± 0.2u2009eV above the VBM is found.

Effect of annealing in reduced oxygen pressure on the electrical transport properties of epitaxial thin film and bulk (La1−xNdx)0.7Sr0.3MnO3

A comparative study of the effect of annealing in reduced oxygen pressure on the electrical transport properties of (La1−xNdx)0.7Sr0.3MnO3 (x=0, 0.25, 0.5, 0.75, and 1) epitaxial thin films and bulk materials has been carried out. The epitaxial films grown by pulsed laser ablation were in situ annealed in an oxygen atmosphere of 2×10−6–760u200aTorr at 700u200a°C for 1 h. It is found that the electrical transport behavior of the epitaxial film is insensitive to the annealing pressure. A similar thermal treatment on the bulk materials at 5 mTorr oxygen ambient, however, caused a dramatic change in their resistivity-temperature dependence. Our results suggest that the annealing has a prominent effect on the properties of grain boundary, which plays an important role in determining the electrical transport behavior of polycrystalline manganites.

Multiferroic and magnetoelectric properties of Bi1−xBaxFe1−xMnxO3 system

Multiferroic compounds Bi1−xBaxFe1−xMnxO3 (0.2 ≤ x ≤ 0.5) have been synthesized by conventional solid-state reaction. X-ray diffraction shows that Bi1−xBaxFe1−xMnxO3 is single phase up to x = 0.4. These samples exhibit magnetism and ferroelectricity simultaneously at room temperature. A considerable enhancement of the polarization on magnetic poling and a dielectric anomaly near the magnetic transition (TC) due to the intrinsic magnetoelectric coupling effect are observed in the Bi0.8Ba0.2Fe0.8Mn0.2O3 sample. The dielectric constant for the Bi0.8Ba0.2Fe0.8Mn0.2O3 sample at room temperature decreases with increasing applied magnetic fields, and the coupling coefficient (e(H) − e(0))/e(0) reaches −0.2% at H = 6 kOe.

Preparation and characterization of iron(III) oxide (α-Fe2O3) thin films hydrothermally

Abstract Thin films (0.12μm) of hematite (α-Fe 2 O 3 ) were prepared on Si(111) and Si(100) substrates by hydrothermal treatment of a solution of iron nitrate containing urea in the temperature range of 100–200 °C for 4–24h. The films consisted of spherical grains for Si (111) and columnar grains for Si(100) with a typical grain size 10nm and 30nm × 5nm, respectively. Both films deposited on Si (111) and Si(100) have (101) preferred orientation.

Epitaxial growth of SrTiO3 films with different orientations on TiN buffered Si(001) by pulsed laser deposition

Epitaxial SrTiO3 (STO) films have been grown on TiN buffered Si(001) by pulsed laser deposition. The TiN layer was in situ deposited at 540, 640 or 720°C whereas the STO film was grown at a fixed temperature of 640°C. We have studied the effect of the growth temperature of TiN on the epitaxial relationship of STO/TiN heterostructures. It is found that for TiN grown at 540 or 640°C the epitaxial relationship is 〈001〉STO ‖ 〈001〉TiN, and for TiN grown at 720°C it changes to (101)STO ‖ (001)TiN and [101]STO ‖ [110]TiN (or [101]STO ‖ [110]TiN). This change of relationship is accompanied by a sharp reduction in the out-of-plane lattice constant of the TiN layer. Fourier transform infrared spectra show that the longitudinal optic modes are active for all the STO films, but the absorption peak associated with the transverse optic mode is observed only in the (101) oriented STO films.

Heteroepitaxial growth and multiferroic properties of Mn-doped BiFeO 3 films on SrTiO3 buffered III-V semiconductor GaAs

Epitaxial Mn-doped BiFeO3 (MBFO) thin films were grown on GaAs (001) substrate with SrTiO3 (STO) buffer layer by pulsed laser deposition. X-ray diffraction results demonstrate that the films show pure (00l) orientation, and MBFO (100)//STO(100), whereas STO (100)//GaAs (110). Piezoresponse force microscopy images and polarization versus electric field loops indicate that the MBFO films grown on GaAs have an effective ferroelectric switching. The MBFO films exhibit good ferroelectric behavior (2Pru2009∼u200992u2009μC/cm2 and 2ECu2009∼u2009372u2009kV/cm). Ferromagnetic property with saturated magnetization of 6.5u2009emu/cm3 and coercive field of about 123u2009Oe is also found in the heterostructure at room temperature.

The role of energetic plasma in pulsed laser deposition of epitaxial manganite films

Epitaxial La0.7Sr0.3MnO3 thin films have been grown on LaAlO3(001) substrates by pulsed laser deposition under different target-plume-substrate configurations. Outgrowths of various shape and size from some of the manganite films are observed. When the substrate is placed within the visible laser-produced energetic plasma plume, the deposited films are outgrowth-free and exhibit good crystallinity and high electrical conductivity. The formation mechanisms and control measures of the outgrowths in pulsed laser deposited manganite films are discussed.

Vacancy defects in epitaxial La0.7Sr0.3MnO3thin films probed by a slow positron beam

Vacancy defects in epitaxial La0.7Sr0.3MnO3 (LSMO) thin films on LaAlO3 substrates were detected using a variable energy positron beam. The line-shape S parameter of the epitaxial thin films deposited at different oxygen pressures was measured as a function of the implanting positron energy E. Our results show that the S parameter of the films changes non-monotonically with their deposition oxygen pressures. For the films deposited at lower oxygen pressures, the increase in S value in the films is attributed to the increase in oxygen vacancies and/or related defect–VO complexes, and for those deposited at higher oxygen pressures, the larger S parameter of the films is caused by the grain boundaries and/or metallic ion vacancies. The surface morphology of the films was also characterized to analyse the open volume defects in the LSMO films.

Surface phase decomposition in Bi2Sr2CaCu2Oy single crystals

Phase decomposition in high‐quality Bi2Sr2CaCu2Oy single crystals has been induced by annealing treatments at a temperature over 500u2009°C. X‐ray diffraction and scanning electron microscope studies show that this change of structure is mainly limited in the surface part of the annealed single crystals and the 2201 phase together with a new phase of cell parameter c=9.6 A segregated from the 2212 phase. The phase decomposition is directly associated with the oxygen content in the annealing atmospheres and evaporation of the Bi is detected and is suggested to be the main factor involving the phase segregation in the annealing process and an important factor for the BiO bilayers in the as‐grown single crystals.