Small-sized Domains Research Articles

Realization of excellent piezoelectricity and high Curie temperature in BF–BT ceramics via structural regulation and domain engineering

BiFeO3–BaTiO3 (BF–BT) is one of the lead-free piezoceramic materials with high Curie temperature (TC) and high polarization. Herein, the (Bi0.5Li0.5Ti)6+ group elements are introduced into the 0.75BiFeO3−0.25BaTiO3 (0.75BF–0.25BT) system to optimize comprehensive performances via optimizing the intrinsic piezoelectric contribution and the extrinsic piezoelectric contribution. For intrinsic piezoelectric contribution, the tetragonal phase ratio of the ceramics is increased. For extrinsic piezoelectric contribution, the grain structures and the domain structures of the ceramics are improved with a relaxor state in which small-sized domains and large-sized domains coexist. The best overall performances are obtained at x = 0.010 with piezoelectric constant d33 ∼ 130 pC/N at room temperature, d33 ∼ 231 pC/N at 313 °C, resistance ρ ∼ 1.49 × 106 Ω cm at 300 °C, and Curie temperature TC ∼ 632 °C that improved significantly. Moreover, when x = 0.010, the piezoelectric thermal stability is also significantly improved, with Δd33 being less than 15% before 200 °C and maintaining 60% of d33 at 400 °C. The present experiments provide a new strategy to investigate the origin of the enhanced piezoelectric response of BF–BT ceramics as well as their applications in the field of high-temperature lead-free piezoelectricity.

Observation of Micro-Scale Domain Structure Evolution under Electric Bias in Relaxor-Based PIN-PMN-PT Single Crystals

Relaxor ferroelectrics play a vital role as functional components in electromechanical devices. The observation of micro-scale domain structure evolution under electric bias in relaxor ferroelectrics has posed challenges due to their complex domain morphology characterized by small-sized domains. The present study aims to investigate the dielectric diffusion–relaxation characteristics, domain structure, and domain switching evolution under electric bias in high-performance single crystals of Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-33PbTiO3. The findings reveal the presence of strip-like domain patterns that interlock irregular small-sized nanodomains in PIN-PMN-33PT single crystals. Furthermore, the sample undergoes three distinct stages under electric bias, including the nucleation of new domains, the gradual forward expansion of domains, and the lateral expansion of domains. These observations provide valuable insights for understanding and exploring domain engineering techniques in relaxor ferroelectrics.

Anomalous photovoltaic effect in Na0.5Bi0.5TiO3-based ferroelectric ceramics based on domain engineering

The anomalous photovoltaic (APV) effect is promising for high-performance ferroelectric materials and devices in photoelectric applications. However, it is a challenge how to tune the APV effect by utilizing the characteristic structure of ferroelectrics. Here, a domain engineering strategy is proposed to enhance the APV effect in lead-free 0.88(Na0.5Bi0.5TiO3)-0.12(Ba1–1.5xSmxTiO3) (NBT-BST) ferroelectric ceramics. By tuning the domain size based on Sm3+ doping, a maximum open-circuit voltage (VOC) of 18.1 V is obtained when Sm3+ content is 0.75%, which is much larger than its bandgap (Eg). The mechanism of this large VOC originates from the multiple positive effects induced by the small-size domain, where decreasing domain size enhances ferroelectric polarization and net interface barrier potential, leading to a large driving electric field. Moreover, the APV effect exhibits a giant temperature sensitivity due to the dramatic evolution of small-size domain in the temperature field. This work sheds light on the exploration of ferroelectrics with APV effect and inspires their future high-performance optoelectronic device applications.

Surfactant-Assisted Synthesis of Mesoporous Metal Phosphonates to Control Surface Properties Including an Opportunity to Organize a Bulky Biphenyl Linker.

A wide variety of properties by the presence of functional organic groups have so far been investigated by using periodic mesoporous organosilica (PMO)-type materials but not yet discussed with surface properties that are controlled through the success in synthesizing analogous non-silica-based hybrid mesoporous materials and subsequent evaluation and/or comparison of their properties. Here, we demonstrated the advance in synthesizing biphenyl group (-Ph-Ph-, also expressed as -2Ph)-containing mesoporous metal phosphonates with a rational understanding of surface properties. Ordered mesoporous films of aluminum and titanium ones (AOP-2Ph and TiOP-2Ph) were fabricated by spin-coating and their powders were recovered by spray-drying with the confined assembly of spherical mesopores. As in the case of PMO-type materials, the possibility to organize a -Ph-Ph- linker at the molecular scale was found in the powder samples of AOP-2Ph and TiOP-2Ph because thick frameworks would give an opportunity to organize the bulky -Ph-Ph- linker as the small-sized domains even around spherical mesopores. Surface properties of AOP-2Ph and TiOP-2Ph were evaluated by using the data of water (H2O) adsorption isotherms and compared with those containing different organic groups. The unique hydrophilicity starting from the hydration of AlO4 units was drastically reduced by the presence of -Ph-Ph- groups with a disappearance of the capillary condensation by the presence of mesopores. In addition, a partial replacement of TiO6 units with AlO4 and/or its hydrated AlO6 species was proposed for decreasing the strong hydrophobicity of TiOP-2Ph. The contact angle over the spin-coated films was also measured by using a droplet of H2O, indicating that the surface of the films, especially TiOP-2Ph, was extremely hydrophilic. Although surface properties at the molecular scale can be evaluated by using molecular H2O vapor during the measurement of H2O adsorption isotherms, the interaction of the H2O cluster (droplet) with the bulk surface seems to be predominated by inorganic moieties.

Domain structure and finite-size effects in Sr2-La FeMoO6 nanoparticles: A study by magnetic measurements

In this work, a model for the microstructure of Sr2-xLaxFeMoO6 nanoparticles samples (0 ≤ x ≤ 0.4) was established based on scanning electron microscopy and magnetic studies. The analysis reveals antiphase crystalline domains in the particles with the size distribution centered around mean values below ∼12 nm for all the samples. Such small-size domains are responsible for the superparamagnetic properties observed for temperatures below room temperature, which are dependent on their dipole interactions. According to the fraction of Fe atoms at the antiphase boundaries calculated under the spherical domain assumption, these domains have lower degrees of atomic disorder than those estimated from the saturation magnetization values at 5 K, which are consistent with the high spin polarization values previously reported. The Curie temperature values, and the broadening of the magnetic phase transition can be satisfactorily explained based on the domain size distribution.

Numerical study on melting of phase change material in an enclosure subject to Neumann boundary condition in the presence of Rayleigh-Bénard convection

This research study investigated the melting process of a phase change material (PCM), heated from the bottom, under Neumann boundary conditions, in the presence of Rayleigh-Bénard convection. The problem was numerically simulated for a range of domain sizes (1×1−8×8cm2) and heat fluxes (0.5−2W/cm2) using the enthalpy porosity technique, which is mostly applicable in cooling heat exchangers of electronic devices. Scaling analysis and the numerical results were employed to find the relationship between the Nusselt number and the solid-liquid interface location with other dimensionless parameters and develop correlations to predict the Nusselt number and the solid-liquid interface location for this type of melting problem. The results of this research could be used to better understand the heat transfer regimes formed during melting in an enclosure heated from the bottom and predict the Nusselt number and the solid-liquid interface location. It was found that the temperature and Nusselt number fluctuations are initiated in the coarsening subregime when the Rayleigh number was not larger than 106 and thus may not occur for small-sized domains. It can be concluded the coarsening and turbulent subregimes may not occur in small enclosures, while the melting process mostly occurs during turbulent subregiem in large enclosures. The numerical results revealed the fastest advance of heat transfer rate and consequently, solid-liquid interface occur during the formation of Bénard cells when the Rayleigh number was on the order of 104. The Nusselt number and solid-liquid interface location correlations developed in this study were later validated using two new cases of numerical data. The results revealed that these correlations could accurately predict the Nusselt number and solid-liquid interface location.

Design and development of high-power piezoelectric ceramics through integration of crystallographic texturing and acceptor-doping

This study demonstrates the integrated approach based upon texturing and acceptor doping for realizing a high-power piezoelectric ceramic with combined soft and hard properties. The textured Mn-doped 0.24 Pb(In1/2Nb1/2)O3-0.42 Pb(Mg1/3Nb2/3)O3-0.34 PbTiO3 (PIN-PMN-PT) ceramic exhibits enhanced piezoelectric coefficient d33 and electromechanical coupling factor k31 in comparison with random counterpart. This enhanced piezoelectric response originates from the combined intrinsic high piezoelectric properties of <001>-oriented grains, and reduced energy barrier for polarization rotation in textured ceramics. The BaTiO3 (BT) template in textured ceramics increases the tetragonality degree which results in improved coercive field Ec but decreased mechanical quality factor Qm in comparison with random counterpart. The decreased Qm values of textured ceramics are related to the crystallographic dependence of Qm and the enhanced domain mobility due to the existence of small size domains. The textured ceramic with 2 vol.% BT content exhibited an excellent combination of soft and hard piezoelectric properties, measured to be: d33 = 517 pC/N, Qm = 1147, Ec = 10.0 kV/cm, and tan δ = 0.49%, which is highly promising for high power piezoelectric applications.

A Regenerative Polymer Blend Composed of Glycylglycine ethyl ester-substituted Polyphosphazene and Poly (lactic-co-glycolic acid).

In the pursuit of continuous improvement in the area of biomaterial design, blends of mixed-substituent polyphosphazenes and poly (lactic acid-glycolic acid) (PLGA) were prepared, and their morphology of phase distributions for the first time was studied. The degradation mechanism and osteocompatibility of the blends were also evaluated for their use as regenerative materials. Poly [(ethyl phenylalanato)25(glycine ethyl glycinato)75phosphazene](PNEPAGEG) and poly [(glycine ethyl glycinato)75(phenylphenoxy)25phosphazene](PNGEGPhPh) were blended with PLGA at various weight ratios to yield different blends, namely PNEPAGEG-PLGA 25:75, PNEPAGEG-PLGA 50:50, PNGEGPhPh-PLGA 25:75, and PNGEGPhPh-PLGA 50:50. The molecular interactions, domain sizes, and phase distributions of the blends were confirmed by atomic force microscopy (AFM) as the PNEPAGEG-PLGA and PNGEGPhPh-PLGA blends showed different domain sizes and phase distributions. Due to the extensive hydrogen bonding within the two polymer components, PNEPAGEG-PLGA exhibited small-sized domains and well-distributed morphology. While for the PNGEGPhPh-PLGA blends, the presence of phenylphenol (PhPh) caused the formation of PLGA large-sized domains as the PLGA formed a continuous phase and PNGEGPhPh constituted a dispersed phase. In addition to AFM results, scanning electron microscopy-energy dispersive X-ray spectrometry (SEM-EDS), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and Fourier transform infrared spectroscopy (FTIR) results demonstrated the miscibility of the blends. The PNEPAGEG-PLGA and PNGEGPhPh-PLGA blends presented in situ 3D interconnected porous structures upon degradation in phosphate-buffered saline (PBS) media at 37°C. However, the blends showed different mechanistic pathways to the formations of the pores. The difference in the erosion patterns could be attributed to the nature of molecular attractions that exist in the blends. Furthermore, the novel blends were able to support cell growth as compared to PLGA, and accommodate cell infiltrations, which ultimately augmented surface area for better cell-material interactions.

Deep learning predicts microbial interactions from self-organized spatiotemporal patterns

Microbial communities organize into spatial patterns that are largely governed by interspecies interactions. This phenomenon is an important metric for understanding community functional dynamics, yet the use of spatial patterns for predicting microbial interactions is currently lacking. Here we propose supervised deep learning as a new tool for network inference. An agent-based model was used to simulate the spatiotemporal evolution of two interacting organisms under diverse growth and interaction scenarios, the data of which was subsequently used to train deep neural networks. For small-size domains (100 µm × 100 µm) over which interaction coefficients are assumed to be invariant, we obtained fairly accurate predictions, as indicated by an average R2 value of 0.84. In application to relatively larger domains (450 µm × 450 µm) where interaction coefficients are varying in space, deep learning models correctly predicted spatial distributions of interaction coefficients without any additional training. Lastly, we evaluated our model against real biological data obtained using Pseudomonas fluorescens and Escherichia coli co-cultures treated with polymeric chitin or N-acetylglucosamine, the hydrolysis product of chitin. While P. fluorescens can utilize both substrates for growth, E. coli lacked the ability to degrade chitin. Consistent with our expectations, our model predicted context-dependent interactions across two substrates, i.e., degrader-cheater relationship on chitin polymers and competition on monomers. The combined use of the agent-based model and machine learning algorithm successfully demonstrates how to infer microbial interactions from spatially distributed data, presenting itself as a useful tool for the analysis of more complex microbial community interactions.

Bismuth-aluminum two-dimensional 2 × 2 compound and its ordered 9 × 9 domains on Si(111) surface

Using scanning tunneling microscopy (STM) observations, it has been found that bismuth and aluminum form the only 2 × 2 ordered structure over the entire Si(111) surface, covering it either with small-sized domains, large-sized domains or ordered 9 × 9 domains depending on the way of formation. This structure can be formed in wide range of temperature, from room temperature to 500 °C, and on various initial surfaces. Angle-resolved photoelectron spectroscopy (ARPES) has demonstrated that the 2 × 2-(Bi, Al) is semiconducting. The structural model of the 2 × 2 has been determined using ab-initio random structure searching method and confirmed by comparison of simulated and experimental STM images as well as experimental ARPES spectrum and calculated energy-band dispersion.

Fast Quadtree Based Normalized Cross Correlation Method for Fractal Video Compression using FFT

In order to achieve fast computational speed with good visual quality of output video, we propose a frequency domain based new fractal video compression scheme. Normalized cross correlation is used to find the structural self similar domain block for the input range block. To increase the searching speed, cross correlation is implemented in the frequency domain using FFT with one computational operation for all the domain blocks instead of individual block wise calculations. The encoding time is further minimized by applying rotation and reflection DFT properties to the IFFT of zero padded range blocks. The energy of overlap small size domain blocks is pre-computed for the entire reference frame and retaining the energies of the overlapped search window portion of previous adjacent block. Quadtree decompositions are obtained by using domain block motion compensated prediction error as a threshold to control the further partitions of the block. It provides a better level of adaption to the scene contents than fixed block size approach. The result shows that, on average, the proposed method can raise the encoding speed by 48.8 % and 90 % higher than NHEXS and CPM/NCIM algorithms respectively. The compression ratio and PSNR of the proposed method is increased by 15.41 and 0.89 dB higher than that of NHEXS on average. For low bit rate videos, the proposed algorithm achieve the high compression ratio above 120 with more than 31 dB PSNR.

Anti-inflammatory, antibacterial, and cytotoxic activity by natural matrices of nano-iron(hydr)oxide/halloysite

This manuscript reports on the effects of natural Fe-halloysite matrices on infiltration and migration of neutrophils (polymorphonuclear (PMN) leukocytes), which, after the skin, constitute the primary protection of organisms against pathogens. Speciation of mineral Fe was quantified before and after treatment with citrate-bicarbonate-dithionite (CBD). Infiltration and migration of inflammatory and immune effector cells, and cell viability were quantified using the 12-O-tetradecanoylphorbol-13-acetate (TPA) and myeloperoxidase (MPO) enzymatic activity methods, and the Griess assay. Halloysite was collected ~2km from Opotiki, Bay of Plenty, New Zealand. HRSEM images confirmed typical morphological features proper of spheroidal Hal (S-Hal). Mössbauer spectroscopy of S-Hal confirmed the presence of Fe, octahedrally coordinated in the form of substituted Fe(III), magnetically ordered goethite or ferrihydrite. HRTEM images showed the presence of small-size domains of Fe (~3-nm) predominantly in the form of ferrihydrite. EPR analyses of S-Hal (0–5000ppm) before and after reacting with desferrioxamine-B confirmed the fast release of Fe from the nanodomains of ferrihydrite. Early inhibition of edema by S-Hal doubled that by CBD treated Hal (t-S-Hal), explained because labile Fe (2-L-ferrihydrite) enhanced the 4-h anti-inflammatory response. On the other hand, prolonged inhibition of edema by S-Hal and t-S-Hal compared, consistent with the release of Fe from the Hal structure. The presence of S-Hal or t-S-Hal related to the inhibition of MPO content. After 4h, the inhibition of MPO content by S-Hal or t-S-Hal compared to that by commercial indomethacin (ca. 80%). S-Hal or t-S-Hal showed high inhibition of MPO contents shortly after exposure, but decreased sharply afterwards. On the other hand, tubular Hal (T-Hal) caused an increasing inhibition of MPO with time, explained because clay structure restricted the kinetics and mechanism of MPO inhibition. Evidenced showed that the release of mineral Fe related to infiltration and migration of inflammatory and immune effector cells, expanding the knowledge that metal ions affect inflammatory responses. Finally, dose–response experiments confirmed that the inhibition of edema and cell viability were surface-mediated. Natural clay reservoirs are complex in composition, therefore identifying the molecular mechanism(s) regulating cell migration and infiltration becomes necessary prior to recommending their use for healing purposes.

Water soluble amino grafted silicon nanoparticles and their use in polymer solar cells

Stable aqueous amino-grafted silicon nanoparticles (SiNPs-NH2) were prepared via one-pot solution method. By grafting amino groups on the particle surface, the dispersion of SiNPs in water became very stable and clear aqueous solutions could be obtained. By incorporating SiNPs-NH2 into the hole transport layer of poly(3,4-ethylenedioxythiophene)/polystyrene sulfonic acid (PEDOT:PSS), the performance of polymer solar cells composed of poly[2-methoxy,5-(2′-ethylhexyloxy)-1,4-phenylene vinylene] (MEH-PPV):[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as active layer can be improved. SiNPs-NH2 are dispersed uniformly in the PEDOT:PSS solution and help form morphologies with small-sized domains in the PEDOT:PSS film. SiNPs-NH2 serve as screens between conducting polymer PEDOT and ionomer PSS to improve the phase separation and charge transport of the hole transport layer. As a result, the sheet resistance of PEDOT:PSS thin films is decreased from (93 ± 5) × 105 to (13 ± 3) × 105 Ω/□. The power conversion efficiency (PCE) of polymer solar cells was thus improved by 9.8% for devices fabricated with PEDOT:PSS containing 1 wt% of SiNPs-NH2, compared with the devices fabricated by original PEDOT:PSS.

A polycrystalline model for magnetic exchange bias

This work introduces a realistic model for the magnetic behavior of polycrystalline ferromagnet/antiferromagnet (FM/AF) systems with granular interfaces. It considers that, for strong enough interface exchange coupling, the AF layer breaks the adjacent FM into small-sized domains and that at the interface there exist grains with uncompensated spins interacting with the FM magnetizations; the classification of these grains as unstable (rotatable, responsible for a coercivity enhancement) or stable (adding to the bias) depends on both the anisotropy and the magnetic coupling with the adjacent FM. The distinctive characteristic of the model is that the effective rotatable anisotropy changes when the external magnetic field is varied resulting in a non-zero hard-axis coercivity, a feature commonly observed, though little understood and often ignored. The applicability of this model was checked on a typical magnetron-sputtered IrMn/Co bilayer and excellent agreement between experiment and simulation was achieved.

Synthesis and Optical Properties of Small Au Nanorods Using a Seedless Growth Technique

Gold nanoparticles have shown potential in photothermal cancer therapy and optoelectronic technology. In both applications, a call for small size nanorods is warranted. In the present work, a one-pot seedless synthetic technique has been developed to prepare relatively small monodisperse gold nanorods with average dimensions (length × width) of 18 × 4.5 nm, 25 × 5 nm, 15 × 4.5 nm, and 10 × 2.5 nm. In this method, the pH was found to play a crucial role in the monodispersity of the nanorods when the NaBH(4) concentration of the growth solution was adjusted to control the reduction rate of the gold ions. At the optimized pH and NaBH(4) concentrations, smaller gold nanorods were produced by adjusting the CTAB concentration in the growth solution. In addition, the concentration of silver ions in the growth solution was found to be pivotal in controlling the aspect ratio of the nanorods. The extinction coefficient values for the small gold nanorods synthesized with three different aspect ratios were estimated using the absorption spectra, size distributions, and the atomic spectroscopic analysis data. The previously accepted relationships between the extinction coefficient or the longitudinal band wavelength values and the nanorods' aspect ratios found for the large nanorods do not extend to the small size domain reported in the present work. The failure of extending these relationships over larger sizes is a result of the interaction of light with the large rods giving an extinction band which results mostly from scattering processes while the extinction of the small nanorods results from absorption processes.

ROLE OF MICROSTRUCTURE AND DOMAIN STRUCTURE ON THE SOFT MAGNETIC PROPERTIES OF MAGNETIC FIELD ANNEALED Fe89-xZr11Bx ALLOYS

We report the evolution of microstructure, domain structure, and soft magnetic properties of amorphous and nanocrystalline Fe 89-x Zr 11 B x(x = 0 - 10) alloys. High-resolution electron microscopy observations reveal that the annealed alloys exhibit a two-phase microstructure. Addition of B enhances the ferromagnetic properties of Fe – Zr amorphous phase in the two-phase structured microstructure, resulting in good soft magnetic properties. Large-sized domains with smooth domain walls are observed in the alloys annealed below 873 K, which exhibit excellent magnetic softness. On the other hand, in the alloys annealed above 873 K, small-sized domains with irregular domain walls and domain wall pinning by Fe – Zr compound are seen. The soft magnetic properties in Fe – Zr – B alloys not only depend on mean grain size, but also on the strength of the intergranular magnetic coupling and structural inhomogeneities.

Comparison of the liquid-ordered bilayer phases containing cholesterol or 7-dehydrocholesterol in modeling Smith-Lemli-Opitz syndrome

The phase behavior of egg sphingomyelin (ESM) mixtures with cholesterol or 7-dehydrocholesterol (7-DHC) has been investigated by independent methods: fluorescence microscopy, X-ray diffraction, and electron spin resonance spectroscopy. In giant vesicles, cholesterol-enriched domains appeared as large and clearly delineated domains assigned to a liquid-ordered (Lo) phase. The domains containing 7-DHC were smaller and had more diffuse boundaries. Separation of a gel phase assigned by X-ray examination to pure sphingomyelin domains coexisting with sterol-enriched domains was observed at temperatures less than 38 degrees C in binary mixtures containing 10-mol% sterol. At higher sterol concentrations, the coexistence of liquid-ordered and liquid-disordered phases was evidenced in the temperature range 20 degrees -50 degrees C. Calculated electron density profiles indicated the location of 7-DHC was more loosely defined than cholesterol, which is localized precisely at a particular depth along the bilayer normal. ESR spectra of spin-labeled fatty acid partitioned in the liquid-ordered component showed a similar, high degree of order for both sterols in the center of the bilayer, but it was higher in the coexisting disordered phase for 7-DHC. The differences detected in the models of the lipid membrane matrix are said to initiate the deleterious consequences of the Smith-Lemli-Opitz syndrome.

Multifractal Description of Nitrogen Adsorption Isotherms

The specific surface area (SSA) of a soil is commonly estimated by the Brunauer–Emmett–Teller (BET) equation, which implies linearity between applied pressure and volume of adsorbate for a restricted scale range. Dinitrogen adsorption isotherms provide useful data for BET analysis, but they also contain additional information that may render useful a multifractal analysis. The objectives of this work were: (i) to find out if differences in soil use intensity cause changes in SSA assessed by the BET method, and (ii) to evaluate the usefulness of multifractal analysis for characterizing N2 adsorption isotherms also used for SSA determination. The study soils were a Vertisol and a Mollisol from Entre Ríos, Argentina. Treatments included: (i) native land never previously cultivated; (ii) permanent pasture; (iii) crop–pasture rotation; and (iv) continuous cropping. Vertisols had significantly greater SSA than Mollisols. Continuous cropping resulted in significant losses of organic matter (OM) content and aggregate stability decay in both soil types. Losses of OM by land use intensification significantly increased SSA in the Mollisol, but this trend was reversed in the Vertisol. All N2 adsorption isotherms exhibited multifractal behavior. Singularity spectra showed strongly asymmetric concave parabolic shapes with a left‐hand side much wider than the right‐hand one. Entropy dimension, D1, values were in the range 0.357 to 0.558 for the Vertisol and 0.401 to 0.658 for the Mollisol, which indicates that most of the measure concentrates in a small size domain. Several multifractal parameters were significantly different between soil types and soil use intensities.

Exchange Effect in TM-TbCo/RE-TbCo Double Layer Films

The High saturation magnetization (Ms) media are desired to yield large flux density for high resolution giant magnetoresistive head readout in Heat Assisted Magnetic Recording (HAMR). To ensure adequate stability of small size domains, the media for HAMR should possess large coercivity (Hc). In this work, we study of interface wall energy and the behavior of the magnetization of each layer in exchange coupled doubled-layered (ECDL) films. The Tb17Co83 (90 nm)/Tb30Co70 ECDL films with different Tb30Co70 thickness (20, 35, 50, 70, 90 nm) are made to increase the Ms value. As the thickness of Tb30Co70 film increase from 20 to 90 nm, the coercivity of the films increases from 2.5 to 8 kOe. The enhanced coercivity of ECDL films is due to the formation of domain wall at the interface of the ECDL film. As the Tb30Co70 increases from 20 to 90 nm, the Ms value of the films decreases from 380 to 330 emu/cm3. Due to Co has larger magnetic moment than that of Tb at room temperature, the resulting Ms value of the films decreases with increasing the thickness of Tb30Co70 layer.

Performance of Monolithic Silica Capillary Columns with Increased Phase Ratios and Small-Sized Domains

Monolithic silica capillary columns for HPLC were prepared from tetramethoxysilane to have smaller sized domains and increased phase ratios as compared to previous materials, and their performance was evaluated. The monolithic silica columns possessed an external porosity of 0.65-0.76 and a total porosity of 0.92-0.95 and showed considerably higher performance and greater retention factors in a reversed-phase mode after chemical modification than columns previously reported. An octadecylsilylated monolithic silica column with the smallest domain size (through-pores of approximately 1.3 microm and silica skeletons of approximately 0.9 microm) showed a plate height of less than 5 microm at optimum linear velocities (u) of 2-3 mm/s in 80% acetonitrile for a solute having retention factors of approximately 1, and approximately 7 microm at u = 8 mm/s. With a permeability similar to that of a column packed with 5-microm particles, the monolithic silica columns were able to attain column efficiencies comparable to that of particulate columns packed with 2-2.5-microm particles, and showed performance in the "forbidden region" for the previous columns. The performance of the monolithic column can be compared favorably with that of a particle-packed column when 15,000-30,000 or more theoretical plates are desired at a pressure drop of 20-40 MPa or lower. The increased homogeneity of the co-continuous structures, in addition to the small-sized domains, contributed to the higher performance as compared to previous monolithic silica columns.