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Effect of Ca substitution on the multiferroic properties of non-epitaxially grown polycrystalline Bi1−xCaxFeO3 (BCFO) films on refined Pt(1 1 1) electrode buffered glass substrates is studied. The structural analysis shows that a pure perovskite phase with isotropic orientation is present for BCFO films (x = 0.05–0.15). The grain size and surface roughness are reduced with increasing x. Different from the BCFO ceramics, good ferroelectric properties with the remanent polarization (2Pr) of 91–124 μC/cm2 and electrical coercive field (Ec) of 294–394 kV/cm are obtained in BCFO polycrystalline thin films. Furthermore, the substitution of Ca2+ for Bi3+ effectively enhance the ferromagnetic properties with magnetization (Ms) of 5.9–8.2 emu/cm3 and coercivity (Hc) of 1224–1258 Oe. The ferromagnetic and ferroelectric properties and leakage behavior as functions of Ca content x are discussed.

Non-epitaxially induced perpendicular magnetic anisotropy (PMA) of Co 50 Pt 50 thin films at room temperature (RT) is reported. The CoPt film having a disordered hcp structure shows a magnetocrystalline anisotropy ( K u RT ) of 1–2 × 10 6 erg/cm 3 in a wide range of layer thickness from 2 to 20 nm. K u RT of about 1 × 10 6 erg/cm 3 can be preserved after a 400 °C-thermal cycle in the 5-nm-thick sample. Moderate PMA, large thickness range, simple preparation process, low formation temperature but good thermal stability make presented hcp CoPt become a remarkable option for advanced spintronic devices.

SmCo7-based compounds are prototypical rare-earth based hard magnetic materials that are the backbone of numerous devices and applications. We have found that by doping the SmCo7 phase with Niobium (e.g. SmCo6.7Nb0.3), the enhanced coercivity being measured. Using a combination of microstructural and compositional characterization techniques with ab initio calculations, we find that the Nb-doping stabilizes the nanocrystalline nature of the material by residing at the 2e site of the SmCo7 structure, decreases the average grain size, and substantially increases the magnetocrystalline anisotropy constant (K) (e.g. from 1.25 × 107 erg/cm3 for SmCo7 to 1.40 × 107 erg/cm3 for SmCo6.7Nb0.3). A significant enhancement in coercivity with Nb doping is attributed to the increased K and the reduced grain size.

This paper describes a novel method to non-destructively determine the thickness of thin layer in a non-contact way. A model of wave interference was established based on the multireflection of shear wave in layered system. Furthermore, its expression of reflection coefficient phase was deduced to provide the principle of thickness measurement. A formed laser source by focusing a line on the layer surface was used to generate shear wave, while an electromagnetic acoustic testing (EMAT) sensor was proposed to receive the wave. An example of the method and experimental measurement for comparison is given for a thin steel sheet with the thickness of approximate 0·4 mm. The relative error between the present method and metallography method is less than 4%, which shows laser-EMAT technique is very suitable to non-destructive assess the thickness of the layer.

Many structures or machines interact with some internal nonconservative forces and present asymmetric systems in which the stiffness and damping matrices are asymmetric. Examples include friction-induced vibration and aeroelastic flutter. Asymmetric systems are prone to flutter instability as a result of the real parts of some poles becoming positive when certain system parameters vary.This paper presents a receptance-based inverse method for assigning a number of complex poles of second-order damped asymmetric systems while keeping other unassigned poles unchanged. It uses state-feedback (active damping and active stiffness) to shift the poles to desired locations where all poles have negative real parts. Receptances at only a small, limited number of degrees-of-freedom of the underlying symmetric system are required. Simulated numerical examples indicate that this is an effective method and is capable of assigning negative real parts to unstable poles to stabilise an otherwise unstable second-order dynamic system.

Exchange bias in [Pt/Co]/NiO multilayers were studied as a function of film thickness and [Pt/Co] layer repetition. A strong temperature dependence of the coercivity, H c ,and exchange bias field, H ex, was observed for the thick and thinnest [Pt/Co]/NiO multilayers. While the thinnest [Pt(3 nm)/Co(1.25 nm)] 4 /NiO multilayers exhibits no in-plane exchange bias field, a perpendicular H ex⊥ ∼ -150 Oe at 80 K was measured. By contrast, the thickest [Pt(12 nm)/Co(10 nm)] 1 /NiO multilayers exhibited an in-plane H ex// ∼ -600 Oe (with H ex// ∼ -1300 Oe at 5 K) with no measurable perpendicular exchange bias field. The estimated interfacial exchange coupling energy implies the effective Co layer thickness contributing to the exchange bias is effective only in Co layer in contact with NiO bottom layer. AC susceptibility and the temperature dependence of H ex show that the a 1.25 nm thick Co component enables perpendicular exchange bias with a reduced blocking temperature T B ∼200 K, compared to that (T B ∼250 K) for the thick [Pt/Co]/NiO multilayers. This is attributed to disordered CoPt phases that formed due to intermixing between Co and Pt during deposition.

We have investigated the structures and magnetic properties of as-deposited and annealed [Pt(20 A)/Fe(15 A)]10/Pt(30 nm) multilayers under different End-Hall voltages (VEH = 0 ∼ 150 V). The films deposited with no End-Hall voltage consisted of Fe (a = 2.91 A), Pt (3.96 A), and disordered FePt (a = 3.82 A) phases. Increasing VEH helps compact the individual Fe and Pt layers, while preventing FePt intermixing. However, increasing the annealing temperature to 550 °C resulted in an ordered f.c.t. FePt (a = 3.85 A, c = 3.73 A) phase for films deposited with VEH = 0V, and a mixture of Fe and Pt phases with grain coarsening was found for films prepared with VEH = 150 V. A drastic increase in coercivity (Hc ∼ 4600 Oe) in the annealed sample (VEH = 0 V) is attributed to the formation of FePt phases. A decrease in Hc with increasing VEH indicates that FePt formation may be suppressed via more energetic ion beam bombardment that resulted in the activation barrier of diffusion increasing dramatically. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A series of [Pt(2 nm)/Co(2 nm)]10/Pt(30 nm) multilayers were deposited by using an ion-beam technique. X-ray diffraction and transmission electron microscopy results have shown that as-deposited samples consist of h.c.p. Co and f.c.c. Pt phases. Disordered CoPt3 phases were developed with increasing End-Hall voltage (VEH) that induces greater ion-beam bombardment energy during deposition. This indicates that intermixing of Co and Pt increases with ion-beam bombardment. The coercivities (ranging from 100 Oe to 300 Oe) of Co/Pt multilayers decreased with increasing VEH. After annealing, the formation of CoPt3 was observed in these ion-beam bombarded samples, resulting in lower coercivities (Hc ∼ 50 Oe). The depressed transition temperature of CoPt3 for films deposited with the largest VEH was attributed to distorted CoPt3 structures that appeared with annealing. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In this study, the structural and magnetic properties of exchange coupled nanocomposite FePt-FePt 3 films were investigated. X-ray diffraction and transmission electron microscopy results showed that after rapid thermal annealing (600 °C for 6 minutes), a phase transformation from [Pt+Fe] into composite FePt-FePt 3 phases was obtained. Annealing created an ordered FePt phase that resulted in a large room temperature coercivity (H c ∼ 3200 Oe) compared to the as-deposited film (H c ∼ 20 Oe). While no exchange bias field (H ex ∼ 0 Oe) was measured at room temperature, the annealed sample showed significant H ex ∼ -500 Oe at lower temperatures (150 K ≤ T ≤ 250 K), indicative of exchange coupling between FePt and FePt3. The high blocking temperature (∼ 250 K) indicates FePt 3 exhibits an enhanced Neel temperature. Further increasing the annealing temperature to 700 °C resulted in a reduction of Hex which is attributed to the transformation of FePt3 into the FePt phase at this higher annealing temperature.

We have investigated the structural and magnetic properties of ion-beam deposited polycrystalline NiFe (25 nm)/Fe-oxide (35 nm) bilayers. A film prepared with an assist beam O2 to Ar gas ratio of 0% during deposition had a bottom layer that consisted of pure b.c.c. Fe (a = 2.87 Å) whereas films prepared with 19%O2/Ar and 35%O2/Ar had either Fe3O4(a = 8.47 Å) or α-Fe2O3 (a = 5.04 Å, c = 13.86 Å) bottom layers, respectively. Cross-sectional transmission electron microscopy revealed a smooth interface between the top nano-columnar NiFe and bottom nano-columnar Fe-oxide layer for all films. At room temperature, the observed coercivity (Hc ∼ 25 Oe) for a film prepared with 19%O2/Ar indicates the existence of a magnetically hard ferrimagnetic Fe3O4 phase that is enhancing the plain NiFe (Hc ∼ 2 Oe) by way of exchange coupling. A significant amount of exchange bias is observed below 50 K, and at 10 K the size of exchange bias hysteresis loops shift increases with increasing oxygen in the films. Furthermore, the strongest exchange coupling (Hex ∼ 135 Oe at 10 K) is with α-Fe2O3 (35%O2/Ar) as the bottom film layer. This indicates that the pure antiferromagnetic phases work better than ferrimagnetic phases when in contact with ferromagnetic NiFe. Hex(T) is well described by an effective AF domain wall energy that creates an exchange field with a (1 − T/Tcrit) temperature dependence. Hc(T) exhibits three distinct regimes of constant temperature that may indicate the existence of different AF spin populations that couple to the FM layer at different temperatures.

Microstructure and tribological properties of low-pressure plasma-sprayed (LPPS) ZrO2–CaF2–Ag2O (ZFA) composite coating were studied by means of optical microscope, scanning electron microscope (SEM) with energy dispersive X-ray analysis (EDXA), electron probe microanalyzer (EPMA) and high-temperature reciprocating wear tester. Coating selected for this investigation was 8 wt.% Y2O3 partially stabilized zirconia coating doped with CaF2 and Ag2O as the solid lubricants. The as-sprayed ZFA coating exhibits a typical lamellar structure of ZrO2 and CaF2 constituents, and some amounts of isolated Ag2O particles. ZFA coating possesses a distinct improvement in wear resistance and frictional characteristics as compared to yttria partially stabilized zirconia (YPSZ) coating at elevated temperatures. At 300–700°C, the ZFA coating exhibits lower friction and wear than at room temperature, 200 or 800°C. Ag2O and CaF2 acting as solid lubricants effectively at 300–400 and 600–700°C, respectively, reduce the friction of the composite. But with the increase of temperature up to 800°C, the severe adhesive sliding causes more material transfer and tearing-out of coating, and finally leads to a high friction and wear. The change or wear transition from a microcrack- or microfracture-controlled wear at room temperature and 200°C to plastic deformation- and adhesion-controlled wear at elevated temperatures is quite distinct and is accompanied by a great change in both friction coefficient and wear loss (such as those at 300 or 800°C).

The microstructure and high-temperature tribological properties of low-pressure plasma-sprayed Cr2O3 ceramic coatings undoped or doped with different additives, such as CaF2, Ag2O and ZrO2 were studied. Under the identical plasma-spray condition, the composite coatings doped with additives exhibited a larger thickness and distinctly lower hardness than pure Cr2O3 coating. Within the as-sprayed composites, ZrO2 and Cr2O3 constituents were observed as fine lamellar structures and Ag2O as isolated particles with different gray levels in the back-scattered electron (BSE) mode, while CaF2 appeared as a darker region with a great volume fraction. Some resolidified structure of ZrO2 crystals featured by fine equiaxed or dendritic grains were clearly observed in the ZrO2 lamellae on the cross-section or the polished surface. Friction coefficients of the composite coatings doped with additives were quite high at room temperature and gradually decreased with increasing of temperature. The situation was reversed for the pure Cr2O3 coating. Among the three kinds of Cr2O3-based coatings, Cr2O3–CaF2–Ag2O (CFA) composite coating exhibited the lowest friction and wear characteristics at above 500°C and reached a minimum value of friction coefficient at 800°C. The Ag2O additive was beneficial to improve the adherence and wettability of the CaF2 transfer film to the counterface, while the ZrO2 additive was detrimental to the formation of a complete CaF2 transfer film because of crushing and microfracture debris of ZrO2 crystals on the worn surface at elevated temperature.

Effect of annealing time on the magnetic properties and microstructure of (Fe0.675Pt0.325)84B16 ribbon has been studied. For the as-quenched ribbons (Vs=45 m/s) annealed isothermally at 500 °C, iHc increases from 0.05 kOe for the quenched ribbons to the optimal value of 7.5 kOe after 5 h annealing, but Br increases from 1.2 kG for the as-quenched ribbons to 7.5 kG after 5 h annealing at first, then decreases when the annealing time is over 6 h. From thermal magnetic analyzer (TMA) and high resolution transmission electron microscope (HRTEM), magnetically soft Fe2B and Fe3B were found to coexist with magnetically hard γ1-FePt phase in the ribbons after suitable annealing. The existence of sufficient fine Fe3B with Fe2B phases and the well exchange coupling effect between hard and soft phases are the main cause of the improved remanence and magnetic energy product of the ternary (Fe0.675Pt0.325)84B16 ribbons.

We show that the magnetism of core-shell nanoparticles (made of maghemite, $\ensuremath{\gamma}$-Fe${}_{2}$O${}_{3}$, cores and transition-metal and metal-oxide shells) is altered substantially by the interface, which is a doped iron-oxide layer formed naturally during the seed-mediated synthesis process, a route used typically to produce core-shell nanoparticles. Characteristics fundamental to useful applications, such as the anisotropy and superparamagnetic blocking temperature, were altered substantially with Cu, CoO, MnO, and NiO shells. To ascertain the origin of this behavior, the prototype $\ensuremath{\gamma}$-Fe${}_{2}$O${}_{3}$/CoO core-shell nanoparticles are described in detail. We show that the magnetism originates essentially from an interfacial doped iron-oxide layer formed via migration of shell ions, e.g., Co${}^{2+}$, into octahedral site vacancies in the surface layers of the $\ensuremath{\gamma}$-Fe${}_{2}$O${}_{3}$ core. For this system, an overall Fe ${m}_{\mathrm{orb}}/{m}_{\mathrm{spin}}=0.15\ifmmode\pm\else\textpm\fi{}0.03$ is measured (${m}_{\mathrm{orb}}\ensuremath{\sim}0$ for the Fe-oxides) and an enhanced Co ${m}_{\mathrm{orb}}/{m}_{\mathrm{spin}}=0.65\ifmmode\pm\else\textpm\fi{}0.03$ elucidates the origin of the unexpectedly high overall anisotropy of the nanoparticle. This interfacial layer is responsible for the overall (e.g., bulk) magnetism and provides a perspective on how the magnetism of core-shell nanoparticles manifests from the selected core and shell materials.

The water vapor and gas transport in polyimide films were analyzed using Harmon's model with accounts for case I transport and case II transport. Harmon's model was in good agreement with the experimental data. The diffusion coefficient obtained by Harmon's model was smaller than that obtained by using the short-time slope of mass uptake versus time with the exception of CO2 in polyimide. A comparison of the present model and the dual-mode sorption model, in which populations follow Henry's law and Langmuir type, was made.

A coordinated theoretical and experimental study of the temperature distribution inside a customized vertical Bridgman system for growing β-NiAl crystal has been conducted. The theoretical model accounts for the combined effects of phase change dynamics, the coupled heat transfer processes of conduction, convection and radiation, variable material properties, and complex geometry pertaining to the system. Comparisons between numerical predictions and experimental measurements show satisfactory agreement. The accuracy of the melting temperature of NiAl with stoichiometric composition, along with important processing parameters such as interface curvatures and temperature gradients across the interface, have been discussed in detail. Also assessed are possibilities of improving the solidification process, including coating the ampoule outer wall with a material of high radiative emissivity or decreasing the ampoule wall thickness.

A computational model has been developed for the Bridgman growth process of β-NiAl crystal. The model accounts for heat transfer in the whole furnace system, including the encapsulated fluid between the heater and the ampoule, conjugate heat transfer around and within the ampoule, and phase change dynamics between melt and crystal. To handle the geometrical and physical complexities of the crystal growth processes, a two-level approach has been developed. At the global furnace level, combined convection/conduction/radiation calculations with realistic geometrical and thermal boundary conditions are made inside the whole system. Refined calculations are then made within the ampoule, with the boundary conditions supplied by the global furnace simulations. The present multi-level model can help improve the predictive capabilities for crystal growth techniques by optimizing the use of the computing resources; it allows one to probe the effects of different physical and geometrical variables on the crystal quality.

In crystal growth devices, in order to control the growth defects and compositional homogeneity of the crystal, a thorough understanding of the heat transfer characteristics is required. In this effort, the combined natural convection and conjugate heat transfer in an axisymmetric configuration representative of the container used in float zone devices are numerically simulated. The geometry adopted contains two concentric cylinders, the inner one representing the crystal within which heat conduction takes place, and the outer one being the container wall; between them is the domain of a height-to-width ratio of 40, filled with encapsulated argon gas. The main parameters varied in this study are Rayleigh number (Ra) and heating location. Substantial refinement in grid size, from 61 × 81 to 201 × 301 nodes, has been exercised to assess the numerical accuracy of the solutions. For Ra = 1.25 × 10 4 , steady-state solutions exist regardless of the heating location. For Ra = 1.25 × 10 5 , on the other hand, persistently oscillatory convective patterns appear, exhibiting both co-rotating (buoyancy-induced) cells and contra-rotating (shear-induced) cells. Consequently, the overall heat transfer rates fluctuate in time. The heat transfer fluctuation in the heated region is not as strong as in other regions; however, the magnitudes of the heat flux there are strongly influenced by the heating location, indicating that, in order to maintain a uniform thermal environment, the power level of the heat source needs to be adaptively adjusted according to the heating location. This challenge to the design and operation of the materials processing equipment can be met with the aid of knowledge gained from numerical simulations.

The nanomagnetism of ultrathin Co/Pt multilayer films is set largely by the microstructure and composition of the interface. To examine these finite-size effects on the Co/Pt magnetism, we have made different Co thickness multilayer films using an ion-beam deposition method with controlled ion energies via an End-Hall voltage VEH, and deposited a layer of NiO to examine the nature of the magnetic anisotropy by way of studying the in-plane and perpendicular magnetism. Examining different Co/Pt multilayers made using different VEH ion energies, we have ascertained that 1.2 nm of Co is the minimum thickness required to establish perpendicular magnetic anisotropy PMA and that no intermixing of Co and Pt at their interface is necessary for PMA to occur. First-principles calculations, consistent with the analysis of electron-energy-loss spectrometry with near atomic resolution, indicate that PMA is due to hybridization of Co and Pt at the interface which results in a perpendicular magnetization axis being set in the Co layer due to a significant lowering of the interfacial anisotropy energy. These results point toward an interesting way to tune PMA in ultrathin Co/Pt multilayers.

An unusual enhancement of the antiferromagnetic ordering (N\'eel) temperature is observed in a ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}∕{\mathrm{Co}}_{3}{\mathrm{O}}_{4}$ thin film. This significant increase of the N\'eel temperature indicates an exchange energy of interface spins between the ferromagnet (FM) and antiferromagnet (AF) that is significantly greater than that of spins in the bulk of the film. Exchange bias is established even when the thin film is zero field cooled. Field cooling the film sets a significantly stronger exchange coupling between the FM and AF spins at the interface with a concomitant increase in the exchange-bias field.

A ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}/(\mathrm{Ni},\mathrm{Fe})\mathrm{O}$ thin film exhibits a positive exchange bias when cooled in a zero field and a negative exchange bias when field cooled. With transmission electron microscopy and electron energy loss spectrometry, the composition and magnetic structure has been ascertained and a distribution of magnetization easy axes about the interface extrapolated. The results indicate that the positive exchange bias is from antiferromagnetic interface moments perpendicular to their ferromagnetic counterparts. With field cooling the alignment is put into a parallel configuration resulting in a negative exchange bias.

In this paper, transmission electron energy loss spectrometry was used to explore the possible origins for an atypical temperature dependent positive exchange bias in a Ni80Fe20/NixFe1-xO thin-film when it is zero-field cooled that shows the usual negative exchange bias when it is field cooled.

The microstructure, ordering parameter, and magnetic properties of multilayer [FePt(x)/Os]n films on glass substrate by dc-magnetron sputtering (with x being thickness in nm; Os with a fixed thickness 5 nm; n being the number of layers) have been studied as a function of the annealing temperatures between 300 and 900 °C. The grain size of multilayer films can be controlled by annealing temperature and thickness of the FePt layer with Os space layer. The coercivity as a function of the annealing temperature for samples with n = 1 and pure FePt behaves roughly saturated after annealing above 700 °C. However, for samples with n > 4 the value of Hc seems still increasing with increasing annealing temperature between 600 and 900 °C, and the ordering parameter decreases with increasing the number of Os layers. Our experimental results are reasonably well to describe the effect of strain-assisted transformation.

The strength, polarity, and temperature dependence of the exchange bias field in ferromagnet/antiferromagnet thin film systems depend critically on the nature of the interfacial microstructure. Using ion bombardment during film deposition, we have found a way to modulate the interface microstructure, providing unique control over the exchange bias magnetism. We demonstrate interfacial microstructure modulation in Ni80Fe20/(Ni,Fe)O thin films, where different ion bombardment energies alter the exchange coupling between the (Ni,Fe)O and Ni80Fe20 interfaces. One interface configuration provides positive or negative exchange coupling depending on whether the film was cooled with or without an external magnetic field, while another interface configuration results in the more typical negative exchange coupling independent of the field cooling.

This paper describes a chemical scheme for CdTe compositional analysis based on titration, and an error between 0.06-0.2% has been attained. This technique was applied to analyze the stoichiometry of CdTe single crystals grown by THM. This paper also comments on p-type doping in CdTe, in which electron beam pulse annealing of phosphorus implanted CdTe will be particularly discussed. This has been demonstrated as an efficient way of p-type doping, and a carrier concentration of 5 × 10 19 cm -3 has been obtained.

For diffusion in a real alloy, some concepts of formal percolation theory may need to be reconsidered because the "immobile" atoms are not truly immobile. Our Monte Carlo simulations of vacancy diffusion on bcc lattices show the existence of a relationship between the activation barrier heights for the vacancy-atom exchanges and the effective percolation threshold concentration. In the language of formal percolation theory, we have modeled this problem by varying the immobile species' barrier height from infinity to some finite value and calculating the resulting percolation threshold. When both species of atoms have a finite mobility, however, our results can be interpreted in terms of probabilities for vacancies to escape local clusters in a fixed amount of time. We find that the dynamical behavior undergoes a marked change above and below the formal percolation threshold, but the strength of the percolating cluster is much less important than in formal percolation theory.

Numerical simulation has been conducted for steady-state Bridgman growth of the CdTe crystal with two ampoule configurations, namely, flat base and semi-spherical base. The present model accounts for conduction, convection and radiation, as well as phase change dynamics. The enthalpy formulation for phase change has been incorporated into a pressure-based algorithm with multi-zone curvilinear grid systems. The entire system which consists of the furnace enclosure wall, the encapsulated gas and the ampoule, contains irregularly configured domains. To meet the competing needs of producing accurate solutions with reasonable computing resources, a two-level approach is employed. The present study reveals that although the two ampoule configurations are quite different, their influence on the melt-solid interface shape is modest, and the undesirable concave interface appears in both cases. Since the interface shape strongly depends on thermal conductivities between the melt and the crystal, as well as ampoule wall temperature, accurate prescriptions of materials transport properties and operating environment are crucial for successful numerical predictions.