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The fatigue properties of (Pb0.6Sr0.4)TiO3 (PSrTO) thin films deposited using (La0.5Sr0.5)MnO3 (LSMO) materials as buffer layer were compared with those of the films grown using (La0.5Sr0.5)CoO3 (LSCO) materials as buffer layer. The extent of degradation induced by polarization switching for 1×1010 cycles with 210 kV/cm maximum field, which is four times of coercive field (Ec), is less pronounced for PSrTO/LSMO/Pt(Si) thin films than that for PSrTO/LSCO/Pt(Si) films. This phenomenon is ascribed to the smaller strain induced in PSrTO/LSMO/Pt(Si) materials. Moreover, the pulse response testing indicates that the degradation of the films mainly occurs at PSrTO-to-LSMO (or PSrTO-to-LSCO) interface.

We report a systematic study on the structural and electronic properties of Bi2Te3−xSex topological insulator alloy grown by molecular beam epitaxy (MBE). A mixing ratio of Bi2Se3 to Bi2Te3 was controlled by varying the Bi:Te:Se flux ratio. X-ray diffraction and Raman spectroscopy measurements indicate the high crystalline quality for the as-grown Bi2Te3−xSex films. Substitution of Te by Se is also revealed from both analyses. The surfaces of the films exhibit terrace-like quintuple layers and their size of the characteristic triangular terraces decreases monotonically with increasing Se content. However, the triangular terrace structure gradually recovers as the Se content further increases. Most importantly, the angle-resolved photoemission spectroscopy results provide evidence of single-Dirac-cone like surface states in which Bi2Te3−xSex with Se/Te-substitution leads to tunable surface states. Our results demonstrate that by fine-tuned MBE growth conditions, Bi2Te3−xSex thin film alloys with tunable to...

Bi0.9Pb0.1FeO3 (BPFO) films were grown on SrRuO3 (SRO)/SrTiO3 (STO) substrates. The surface morphology of BPFO films is highly dependent on that of the SRO layer. Though the step height of STO (100) substrate is equal to one unit cell of STO crystal, the height and width of steps on the surface of SRO and BPFO are larger, which supports a step bunching growth mode on both the SRO layer and BPFO films. At zero bias voltage, the BPFO film exhibits a natural dipole polarization toward the SRO layer, which is believed to be due to the negative charge accumulation at the BPFO/SRO interface, and manifests of 71° and 109° but 180° domain walls. Doping of Pb distorted the BPFO crystal lattice to near cubic that weakens the electric anisotropy and forms a two-step flipping process. To complete a 180° dipole flipping procedure, the dipole moment first rotates 71° to adjacent states followed by a 109° rotation to the final 180° state.

The thermodynamic parameters of domain relaxation process in the absence of external electric fields are related to the intrinsic electrostatic and stress/strain conditions inside the materials, such as the states at surface, states at interface with the electrode, and the atomic defects in the bulk. In order to perform systematical studies of these intrinsic effects, we investigated domain relaxation in a monodomain environment, which was obtained in strained epitaxial BiFeO3 (BFO)(111) films. Without as-grown domain walls and grain boundaries, the epitaxial BFO(111) film provided an ideal system for the dynamic observation of 180-degree domain wall motion. Nano-domains were initially created by writing voltage pulses under the tip of a scanning force microscope and then relaxed through time. The downward polarized domains exhibited much better retention behaviors than the upward domains. A two-step backswitching process was observed, and the behaviors varied with the initial domain sizes. Surface potential measurement showed the dissipation of surface screen charges with time, which was strongly coupled with the 1st step relaxation. The asymmetry behaviors for upward and downward backswitchings, and the two-stage relaxation processes can be explained by the mobile vacancies and the redistribution of surface charges. This study provides the basic understanding of the role of surface charges during the ferroelectric domain relaxation.

In this study, we investigated the magnetoelectric coupling effect in Ni80Fe20∕BaTiO3 (NiFe/BTO) bilayer films. Two different samples with interface roughnesses of about 5 and 20nm were synthesized by controlling the BTO deposition rates. The electrostatic force microscope scanning shows an intrinsic surface potential about 0.2V existing in both NiFe/BTO bilayer films. This phenomenon is due to the bond charge induced by interface dipole moments as the interface-bonding model predicted. The films show good ferroelectric properties, but the hysteresis shows bias asymmetry due to the interface effect. The magnetic coercive fields of NiFe/BTO system increase with the interface roughness. The large magnetoelectric coupling is observed from an irregular change of magnetization near the ferroelectric Curie temperature. The multiferroic properties were enhanced by the interface geometry.

NiFe inserted layer with different thicknesses on the dielectric properties of multiferroic AlN∕NiFe∕AlN multilayer films fabricated on the B270 glass substrates by the reactive sputtering technique was studied. The variation of dielectric constant for multilayer films is dependent on the thickness of the NiFe inserted layer observed from 40Hzto30MHz. In this work, single AlN layer exhibits dielectric constant value of around 6.5. However, we find that the dielectric constant of the AlN∕NiFe∕AlN multilayer films is raised up to 60 for even with a 1nm thick NiFe inserted layer. Additionally, this work also indicates that the dielectric tunability of AlN∕NiFe∕AlN films is dependent on the external magnetic field. These results conclude some magnetoelectric properties of AlN films those in relation to the NiFe ferromagnetic inserted layer. Possible mechanisms for the enhanced dielectric constant in the AlN∕NiFe∕AlN films have been discussed in the paper.

The ferromagnetic resonance (FMR) behaviors for Ni80Fe20 Permalloy films with a wide thickness range from 30to360nm were investigated. The FMR measurements were performed by a vector network analyzer (VNA) technique with scanning frequency at a specified external field. The measured frequency response was fitted well by the theoretical precession conditions. The FMR results show that the effective saturation magnetization, μ0Meff, increases from 1.01to1.36T, while the film thickness varies from 30to360nm. A discontinuous transition is observed at the thickness of 90nm, which corresponds to the transformation boundary of domain wall from Neel to Bloch type in Permalloy films. Meanwhile, the variation of damping coefficient with film thickness also shows a discontinuity at 90nm. For films thinner than 90nm, the dampings vary insignificantly with film thickness. For films thicker than 90nm, the damping coefficient varies linearly with the thickness. The result could be explained by the magnon scattering thro...