J. Z. Liu

Magnetoelectric CoFe2O4-lead zirconate titanate thick films prepared by a polyvinylpyrrolidone-assisted sol-gel method

Magnetoelectric CoFe2O4-PZT (lead zirconate titanate) films as thick as 1 mu m have been prepared by spin coating using a PZT sol-gel solution containing polyvinylpyrrolidone and CoFe2O4 powder. X-ray diffraction result reveals that there exists no chemical reaction or phase diffusion between the CoFe2O4 and PZT phases. The scanning electron microscopy observation confirms that the composite thick film is crack-free and has a well-defined microstructure. The composite thick films exhibit good magnetic and ferroelectric properties, as well as distinct magnetoelectric coupling behavior. The magnetoelectric coupling mechanism for the present composite thick film is discussed in detail. (c) 2006 American Institute of Physics.

Strong magnetoelectric coupling in multiferroic BiFeO3–Pb(Zr0.52Ti0.48)O3 composite films derived from electrophoretic deposition

The BiFeO3–Pb(Zr0.52Ti0.48)O3 composite film in which BiFeO3 nanoparticles are distributed in the Pb(Zr0.52Ti0.48)O3 matrix was prepared by electrophoretic deposition method. The microstructural characterization revealed the structural distortion of the BiFeO3 phase, induced by the unique BiFeO3–Pb(Zr0.52Ti0.48)O3 core/shell structure. The composite film exhibited evidence of ferroelectricity with enhanced ferromagnetism as well as a magnetoelectric effect. The two origins for the magnetoelectric effect are presented. This present work provides a promising roadmap to improve the magnetoelectric effect of BiFeO3-based multiferroics for actual applications.

Strong magnetoelectric coupling in Tb–Fe∕Pb(Zr0.52Ti0.48)O3 thin-film heterostructure prepared by low energy cluster beam deposition

The magnetoelectric Tb-Fe/Pb(Zr(0.52)Ti(0.48))O(3) thin-film heterostructure was prepared by low energy cluster beam deposition. The microstructures, ferroelectric property, leakage current, and magnetization, as well as magnetoelectric effect were investigated for the heterostructure. It is shown that the thin-film heterostructure displays the well-defined microstructure with clear interface. The heterostructure not only exhibits good ferromagnetic and ferroelectric properties, but also possesses strong magnetoelectric effect. The present work provides an ideal avenue to prepare magnetoelectric composite films and facilitates their applications on the microelectromechanical system devices

MICROSTRUCTURE OF OUTGROWTHS ON THE SURFACE OF LASER-ABLATED YBA2CU3O7 THIN-FILMS

Abstract The microstructure of the outgrowths on the surface of pulsed laser ablated YBa 2 Cu 3 O 7 (YBCO) thin films deposited on (100) Y stabilized zirconia substrates was studied by transmission electron microscopy. The outgrowths consist of misaligned superconducting c -axis YBCO grains and a -axis YBCO grains, non-superconducting CuO, Ba 2 CuO 3 , BaCuO 2 , CuYO 2 and Y 2 BaCuO 5 grains about 0.1–5 μm in size. The Y-123 type outgrowths are block-shaped misaligned with the YBCO matrix. The non-superconducting grains mostly are semi-spherical in shape and have a certain crystallographic relation with the YBCO matrix. The protruding heights of the outgrowths on the surface of the film are about 50–450 nm.

Correlation between distribution of outgrowths and microwave surface resistance for YBa2Cu3O7 thin films

A model was proposed to describe the effects of surface outgrowths on the microwave surface resistance of high Tc superconducting thin films. Calculated with experimental data the microwave surface resistance at 10 GHz for c‐axis oriented YBa2Cu3O7 thin films with no outgrowths could be as low as 70 and 4 μΩ at 77 and 4.2 K, respectively. The effect of the orientation of the surface outgrowths on the microwave loss has been discussed.

Effect of structure and morphology on resistive loss at 10 GHz of the large‐area laser‐deposited YBa2Cu3O7 thin films

Three large‐area YBa2Cu3O7(YBCO) superconducting thin films have been laser‐deposited under almost identical conditions. However, the microwave surface resistance Rs of the films deviated greatly, they are 280 μΩ, 3.78 mΩ, and 97 mΩ, respectively. It was found that the structure and morphology of the films greatly influence the resistive losses at 10 GHz and 77 K of the YBCO thin films. Different loss mechanisms were discussed. For high Rs, the large angle grain boundaries were the dominate defect in the thin films and increased the Rs of the film markedly. For low Rs, it was mainly due to the misaligned ‘‘123’’ grains in the thin films and the intrinsic loss. For Rs up to the mΩ range, besides the misaligned 123 grains, domain boundaries and nonsuperconducting outgrowths of different sizes appeared and this caused the rise of Rs value. All these results were given experimentally and discussed theoretically.

Microstructural features at the interface between laser ablated YBa2Cu3O7 films and LaAlO3 substrates

The microstructure at the interface between YBa2Cu3O7(YBCO) thin film and (100)LaAlO3 substrate has been investigated by using transmission electron microscopy. It has been observed that two distinct microstructural features existed in the interface: (1) A thin transitional layer of Ba3Al2O6 was frequently observed and the YBCO thin film grown on it showed stacking faults. (2) Sharp interface with no transitional layer was also occasionally observed and the YBCO film grown on it was single crystalline. In rare cases, a low symmetry phase was observed near the surface of the LaAlO3 substrate, however, the distortion caused by the lattice mismatch between this phase and the YBCO did not affect the quality of the YBCO thin film.

SCANNING-TUNNELING-MICROSCOPY OF LASER-DEPOSITED YBA2CU3O7 THIN-FILMS ON Y-STABILIZED ZIRCONIA SUBSTRATE

The surface morphology and growth mechanism ofc-oriented YBa2Cu3O7 thin films deposited on Y-stabilized zirconia substrate by laser deposition has been investigated with scanning tunneling microscopy. Both screw dislocation and layered island growth processes took place. Surface features such as screw dislocation, steps, subgrain boundaries, holes, and troughs were present, suggesting that they may act as pinning sites for flux lines. A thin layer of nonsuperconducting material with a thickness of a few angstroms is seen on the surface of the film.

The growth mechanism of pulsed laser deposited and DC magnetron sputtered high Tc YBa2Cu3O7 thin films

Abstract The investigation of growth mechanism of pulsed laser deposition (PLD) and magnetron sputtered high T c YBa 2 Cu 3 O 7 (YBCO) thin films were carried out by atomic force microscopy (AFM). Observations showed that the nucleation and growth of the YBCO thin films have the customary island and coalescence mode. For PLD films, both screw dislocation islands and terrace islands occurred, but for the magnetron sputtered thin films only. screw dislocation islands were present. All the islands consist of many steps with a height of one or multiple c-axis unit cell, which indicated that the film grow unit cell by unit cell.

Structures, electrical properties, and equation of state in Ca4Mn3O10 under high pressure

The structure changes and electrical properties in Ca4Mn3O10 under high pressure at room temperature have been studied using energy-dispersive x-ray diffraction with synchrotron radiation and resistance and capacitance measurements. A phase transition from an orthorhombic to a tetragonal phase occurred during increasing pressure to above 19.3 GPa. The equation of state of Ca4Mn3O10 was obtained from the V/V0–P relationship. The bulk modulus B0 and its first-order derivative B0′ of Ca4Mn3O10 were calculated based on the Birch–Murnaghan equation.