Microscopic Domain Structure Research Articles

Injectable and Biodegradable Nanohybrid Polymers with Simultaneously Enhanced Stiffness and Toughness for Bone Repair

AbstractA series of novel injectable and photo‐crosslinkable poly(propylene fumarate) (PPF)‐co‐polyhedral oligomeric silsesquioxane (POSS) copolymers are synthesized via two‐step polycondensation to improve both stiffness and toughness and to promote biological performance of bone tissue engineering scaffolds. The viscoelastic behavior of uncrosslinked PPF‐co‐POSS and the thermal, mechanical, and surface characteristics of photo‐crosslinked PPF‐co‐POSS are investigated as well as the degradation behavior and microscopic POSS domain structures at various weight compositions of POSS (ϕPOSS). Tensile and compressive moduli and facture toughness are enhanced for crosslinked PPF‐co‐POSS when POSS nanocages are well distributed and their crystallinity is completely confined in the networks. Decreases in these mechanical properties are observed at higher ϕPOSS because of decreased crosslinking density and larger POSS aggregates. The mechanical properties are correlated with in vitro mouse pre‐osteoblastic MC3T3‐E1 cell functions including cell attachment, spreading, proliferation, differentiation, and gene expression, which all maximize at ϕPOSS of 10%.

Magnetization Reversal in Ferromagnetic Thin Films

The magnetization reversal mechanism of the magnetic films system with the different magnetic anisotropy, exchange coupling, interface coupling, etc. has been simulated by Monte-Carlo method. The results show that the decrease of magnetic anisotropy is in favor of motion of domain walls, but is not conducive to consistent rotation. The interface coupling of both the ferromagnetic film and the antiferromagnetic film are helpful to the motion of domain walls while the antiferromagnetic film coupling is the more effective. Meantime, the evolution of the microscopic magnetic domain structures has been inspected intuitively while the system is in the process of magnetization.

Epitaxial Pb(Zr,Ti)O3 Thin Films on Flexible Substrates

It is well known that the piezoelectric properties of a thin film can be influenced by crystallographic texture. At the extreme case, epitaxial thin films can be deposited on single crystal substrates (with appropriate lattice matching) to effectively achieve a single crystal thin film. Here, the maximum advantage of orientation dependence is found. Typically this has required small, expensive single crystalline substrates. In the past 10 years, however, the technique of ion beam assisted deposition has been developed for applying a biaxially textured template to an arbitrary smooth surface. This has opened up a new realm of materials integration possibilities, with the prime example being high‐temperature superconducting wires. Here, the same template is utilized for deposition of epitaxial Pb(Zr,Ti)O3 thin films onto LaNiO3 and La0.7Sr0.3MnO3‐coated flexible substrates. Chemical solution deposition (CSD) is used to produce PZT thin films with very high (00l) orientation and excellent in‐plane orientation. Macroscopic ferroelectric measurements depict very square hysteresis behavior, with high remnant polarization of ~40 μC/cm2. Piezoresponse force microscopy and local hysteresis measurements were used to image the microscopic domain structure and to demonstrate the piezoelectric behavior in these materials.

Direction detectable static magnetic field imaging by frequency-modulated magnetic force microscopy with an AC magnetic field driven soft magnetic tip

Direction detectable static magnetic field imaging, which directly distinguishes the up and down direction of static perpendicular magnetic field from a sample surface and the polarity of magnetic charges on the surface, was demonstrated for CoCrPt-SiO2 perpendicular magnetic recording media based on a frequency-modulated magnetic force microscopy (FM-MFM), which uses a frequency modulation of the cantilever oscillation induced by an alternating force from the tip-sample magnetic interaction. In this study, to generate the alternating force, we used a NiFe soft magnetic tip driven by the ac magnetic field of a soft ferrite core and imaged the direction and the amplitude of the static magnetic field from the recorded bits. This method enables measurement of the static magnetic field near a sample surface, which is masked by short range forces of the surface. The present method will be effective in analyzing the microscopic magnetic domain structure of hard magnetic samples.

Three dimensional phase field study on the thickness effect of ferroelectric polymer thin film

The electromechanical behavior of poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] ferroelectric thin film was investigated using the three dimensional (3D) phase-field method. Various energetic contributions, including elastic, electrostatic, and domain wall energy were taken into account in the variational functional of the phase field model. Evolution of the microscopic domain structures of P (VDF-TrFE) polymer film was simulated. Effects of the in-plane residual stress, the film thickness and externally applied electric bias field on the electromechanical properties of the film were explored. The obtained numerical results showed that the macroscopic responses of the electric hysteresis loops are sensitive to the residual stress and electric bias field. It was also found that thickness has a great effect on the electric hysteresis loops and remanent polarization.

Monte Carlo simulation on ferroelectric response to magnetic field in an elastic Ising spin chain

The fantastic ferroelectric response to the magnetic field observed in Ca3CoMnO6 compound, where the ferroelectricity is driven by the collinear magnetism, is investigated by using Monte Carlo simulation based on a one-dimensional elastic Ising model. The microscopic domain structures of spins and ionic displacements are evaluated at different temperatures under different external magnetic fields. It is revealed that the up-up-down-down (↑↑↓↓) spin domains clamped with the domains of ionic displacement are responsible for the exotic ferroelectric behavior upon different magnetic fields in the low temperature range.

Single-crystal-like, c-axis oriented BaTiO3 thin films with high-performance on flexible metal templates for ferroelectric applications

Epitaxial, c-axis oriented BaTiO3 thin films were deposited using pulsed laser ablation on flexible, polycrystalline Ni alloy tape with biaxially textured oxide buffer multilayers. The high quality of epitaxial BaTiO3 thin films with P4mm group symmetry was confirmed by x-ray diffraction. The microscopic ferroelectric domain structure and the piezoelectric domain switching in these films were confirmed via spatially resolved piezoresponse mapping and local hysteresis loops. Macroscopic measurements demonstrate that the films have well-saturated hysteresis loops with a high remanent polarization of ∼11.5 μC/cm2. Such high-quality, single-crystal-like BaTiO3 films on low-cost, polycrystalline, flexible Ni alloy substrates are attractive for applications in flexible lead-free ferroelectric devices.

Domain Structures and Phase Diagram in 2D Ferroelectrics Under Applied Biaxial Strains - Phase Field Simulations and Thermodynamic Calculations

Absract:The microscopic domain structures in 2D ferroelectrics under applied biaxial strains are investigated using a phase field model based on the time-dependent Ginzburg-Landau equation that takes both long-range electric and -elastic interactions into account. The stable polarization patterns are simulated at different temperatures and applied inequiaxial strains. The results show that the ferroelectrics transfer from multi-domain state to single-domain state when temperature surpasses a critical value. On the other hand, the macroscopic equilibrium polarization states are also studied through a nonlinear thermodynamic theory. The corresponding transition from a1, a2 state (p1 ≠ 0, P2 ≠ 0) to a1 state (p1 ≠0, P2 = 0) or a2 state (p2 ≠ 0, P2 = 0) is also found from the “strain-straintemperature” phase diagram, which is constructed by minimizing Helmholtz free energy.

Microscopic domain structures in unidirectional and isotropic exchange-coupled NiO/NiFe bilayers

The dependence on nickel oxide thickness in unidirectional and isotropic exchange-coupled NiO/NiFe bilayer films was investigated by magnetic force microscopy to better understand exchange biasing at microscopic length scales. As the NiO thickness increased, the domain structure of unidirectional biased films formed smaller and more complex in-plane domains. By contrast, for the isotropically coupled films, large domains generally formed with increasing NiO thickness including a new cross type domain with out-of-plane magnetization orientation. The density of the cross domain is proportional to exchange biasing field, and the fact that the domain mainly originated from the strongest exchange coupled region was confirmed by imaging in an applied external field during a magnetization cycle.

Investigation of exchange bias in FeMnC/FeMn bilayers

The exchange bias (EB) effect and magnetic domain structures of FeMnC/FeMn bilayers prepared by a facing target sputtering system were studied. Unusual doubly shifted hysteresis loops were observed in a series of FeMnC/FeMn bilayers when different magnetic fields were applied to induce the exchange bias. The temperature dependences of the double shifted loops were measured and the ferromagnetic resonance measurement reveals the existence of EB. The correlation between the microscopic domain structures and the magnetization reversal processes was discussed, which suggests that the domain structure distribution of the antiferromagnetic layer is responsible for the loop shift.

Microscopic view of a two-dimensional lattice-Gas ising system within the grand canonical ensemble

A reversible 2D critical transition is observed on the GaAs(001) surface and modeled as a lattice-gas Ising system. Without depositing any material, 2D GaAs islands spontaneously form. The order parameter, four critical exponents, and coupling energies are measured from scanning tunneling microscope images of the microscopic domain structure and correlation functions as a function of temperature and pressure. Unprecedented insight into the domain structure of a 2D Ising system through the critical point and a complete Hamiltonian for modeling the GaAs(001) surface are presented.

High-resolution neutron diffraction evidence for strain-induced microdomains during the phase transition in UNi 2Sn

Neutron diffraction shows that abundant strains occur at the cubic to orthorhombic phase transition in UNi 2Sn. This, together with Bragg diffraction line broadening due to small domain size, confirms the presence of a microscopic domain structure in UNi 2Sn that has been postulated in previous investigations. From the direct observation of mobility of structural domain walls in previous work, and the lower limit of the domain size in the present work, a minimum domain wall velocity of 7 m s −1 is deduced. This velocity is very low compared to the sound velocity.

Domain structure and dynamic heterogeneities of a polyethylene acid ionomer by two‐dimensional solid‐state NMR

AbstractTwo‐dimensional wideline separation (WISE) NMR spectroscopy was employed to investigate the microscopic domain structure of an ethylene‐containing acid ionomer, poly(ethylene‐co‐methacrylic acid). Crystallinities were determined from deconvolution of the proton dimension lineshapes, and domain sizes were computed from proton spin diffusion behavior. The time‐scale for spin diffusion between the acid groups and the amorphous regions is less than 1 ms, because the methacrylic acid groups are situated in the amorphous domains. On the other hand, communication between amorphous and crystalline domains requires several milliseconds, consistent with crystalline domain sizes of ca 4 nm. The presence of intermolecular hydrogen‐bonded cross‐linking is clearly detected by the broad proton linewidth associated with the rigid methacrylic acid groups. It is shown that imbibed hexadecane, which strongly plasticizes the amorphous regions of the copolymer, has little effect on crystallinity, crystalline domain sizes or cross‐link sites.

Scanning probe microscope imaging of polyaniline thin films in non‐contact mode

AbstractThe structure of electropolymerized thin films of polyaniline has been studied using the techniques of contact and non‐contact scanning probe microscopy (SPM). Films exposed to Ir+ cations in solution, as well as unexposed films, were examined. Contact‐mode SPM images of these films reveal only a diffuse, amorphous surface structure in both types of film, while non‐contact SPM images indicate an intricate, nanometer‐scale domain structure. Film growth is in a layer‐by‐layer mode, with each layer consisting of small polymer bundles of average dimension 1000 ± 75 Å. The Ir+ incorporation in these films does not involve a restructuring of the film morphology. The relevance of the microscopic domain structure to models describing conduction mechanisms in these films is also discussed.

Magnetic domains along shear bands in amorphous metals observed by spin-polarized scanning electron microscopy

A novel spin-polarized scanning electron microscope with capabilities of observing microscopic domain structures and determining in-plane magnetization directions has been used to investigate the stress-induced magnetic domains in the Fe78B13Si9 (Allied 2605-S2) metallic glass. The magnetic structure in the vicinity of shear bands that are produced near a Mode III crack has been examined. On the tensile side of bending, arrays of individual, discontinuous magnetic “islands” of similar shape and size (about 2–10 μm in length, 3 μm in width, and spaced about 2–4 μm apart) are uniformly distributed on one side of the shear bands. Their easy axis is about parallel to the shear bands. On the other hand, well-defined elliptical domains are found between shear bands on the compression side of bending. Their easy axes are approximately perpendicular to the shear bands. These results suggest the existence of isolated defects of similar stress fields located along the shear bands. The possibility that these defects are dislocations will be investigated next.

Applications of electron holography to multilayer interfaces

Electron holography has received renewed interest recently as a means of resolution enhancement in high resolution phase contrast imaging and as a technique for imaging microscopic magnetic domain structures. Some of the original applications of the technique involved measurement of the absolute mean inner potential in films of known thickness. This approach has now been extended in order to gain information about changes in elemental concentrations at interfaces in multilayer films.The abruptness of interfaces in multilayer films used for X-ray mirrors strongly affects their reflective properties. Previous studies using high resolution phase contrast imaging have shown that this interface diffuseness can be imaged, but typically with low contrast and an unknown contribution from amplitude contrast effects. The differences in mean inner potential between successive layers suggests that the variation of the mean inner potential across the interface should be a good measurement of the change in elemental concentration.

Unexpected magnetization processes in YIG + Co films

Unidirectional properties (shifts of BH loop) were observed in (YCa) 3(FeCoGe) 5O 12 films grown on (100) GGG substrate. These shifts could be flipped by an external field (≈ 50 Oe) applied along the normal to the film or in the sample plane. The properties are similar to those of magnetic materials characterized by unidirectional anisotropy (e.g. exchange-coupled soft and hard magnetic system). The proposed domain structure model of a homogeneous sample with mixed magnetic anisotropy explains these peculiarities reasonably well. The formula for the estimation of a self-biasing field vector is given for a multi-easy axes magnet. The magnetization processes were investigated using the Faraday effect (domain structure image was analyzed visually and digitally), low frequency magnetic susceptibility technique and a vibrating sample magnetometer. The room temperature FMR spectra and the Faraday rotation spectra were analyzed, too. Microscopic theory and domain structure model are discussed for the explanation of the previously reported effects: (i) unexpectedly low and changeable domain wall velocity v ( v, which depends on the width of the applied field pulses, is in the approximate range 1 ßm/s-220 m/s); (ii) domain structure shape memory.