Thickness Of Soft Layer Research Articles

Hysteresis Loops, Critical Fields and Energy Products for Exchange-spring Hard/soft/hard Trilayers

Macroscopic hysteresis loops and microscopic magnetic moment distributions have been determined by a three-dimensional (3D) model for exchange-coupled Sm-Co/α-Fe/Sm-Co trilayers with in-plane collinear easy axes. These results are carefully compared with the popular one-dimensional (1D) micromagnetic models and recent experimental data. It is found that the results obtained from the two methods match very well, especially for the remanence and coercivity, justifying the calculations. Both nucleation and coercive fields decrease monotonically as the soft layer thickness L s increases while the largest maximum energy product (roughly 50 MGOe) occurs when the thicknesses of hard and soft layers are 5 ㎚ and 15 ㎚, respectively. Moreover, the calculated angular distributions in the thickness direction for the magnetic moments are similar. Nevertheless, the calculated nucleation and pinning fields as well as the energy products by 3D OOMMF are systematically smaller than those given by the 1D model, due mainly to the stray fields at the corners of the films. These demagnetization fields help the magnetic moments at the corners to deviate from the previous saturation state and facilitate the nucleation. Such an effect enhances as Ls increases. When the thicknesses of hard and soft layers are 10 ㎚ and 20 ㎚, respectively, the pinning field difference is as large as 30%, while the nucleation fields have opposite signs.

Substantial reduction in coercivity of perpendicular CoPt/FePt graded films with near-atomic flatness on glass substrates

Perpendicular graded films comprising soft Co66Pt34 layer and hard L10-FePt layer deposited on glass substrates were investigated. Microstructure observations reveal the unidirectional growth of the CoPt layer on (001) FePt film. By controlling the deposition temperature of soft layer and interlayer diffusion, the substantially reduced coercivity (Hc) and the near-atomic flatness of surface morphology are simultaneously obtained. In comparison to the single-layered FePt, Hc of the optimal graded film is significantly reduced by a factor of 4, while the surface roughness of the graded film lower than 0.3nm is obtained. Depth-resolved techniques prove that the gradation of L10 ordering could lead to the reduction of Hc and switching field distribution due to the enhancement of interlayer exchange coupling. Well exchange-coupled graded films are characterized at a soft layer thickness within 20nm.

Co/Pd]-CoFeB exchange spring magnets with tunable gap of spin wave excitations

Exchange spring magnets, consisting of a [Co(0.5 nm)/Pd(1 nm)]5 multilayer with perpendicular magnetic anisotropy and a Co20Fe60B20 film with easy plane anisotropy, of variable thickness tCFB, are investigated using Brillouin light scattering. On reducing tCFB in the range 0.8–2.3 nm, the spin-wave frequency gap displays a remarkable increase from nearly 4–48 GHz, reflecting the corresponding rapid growth of the tilting angle of the magnetization with respect to the film normal. These findings are interpreted using a one-dimensional model in which each atomic layer is assumed to be uniformly magnetized, subjected to an effective out-of-plane or easy-plane anisotropy depending on the layer position in the stack, and exchange coupled to its two nearest neighbour atomic layers. With respect to previously investigated [Co/Pd]-NiFe hybrid magnets, a largest frequency tunability, restricted to a narrower range of the soft layer thickness, is observed.

Determination of the resonance frequency – thickness relation based on the ambient seismic noise records from Upper Silesia Coal Basin

Abstract In this paper the Horizontal-to-Vertical Spectral Ratio (HVSR) method and seismic data were applied to evaluate the resonance frequency - thickness relation. The HVSR method was used to estimate the parameters of site effects: amplification and resonance frequency from seismic noise records. The seismic noise was generated by artificial source occurring in Upper Silesia Coal Basin (UBSC), Poland, such as: traffic, industry, coal plants etc. The survey points were located near the Faculty of Earth Sciences in Sosnowiec, Bytom and Chorzow. Based on Albarello’s statistical test the observed H/V maxima was confirmed or rejected. Resonance frequencies were compared with available thicknesses of soft layer obtained by seismic survey (Mendecki 2012). Finally, the estimated resonance frequency - thickness relation for UBSC area showed quite similar power function coefficients as those obtained by other authors

Magnetic properties of L10-FePt/Fe exchange-coupled composite nanodots

The magnetic properties of L10-FePt/Fe exchange-coupled composite (ECC) nanodots were investigated by Hall effect measurement due to its high sensitivity. The FePt/Fe nanodots showed coercivity changing irregularly with respect to the Fe thickness, which deviated from the simulated results, where the coercivity of the ECC dots reduced with increasing Fe soft layer thickness. It was found that the edge damage induced by ion milling affected the coercivity of the nanodots significantly and the magnetization reversal mechanism. Domain wall nucleation and propagation was revealed in the FePt single domain dots. In the FePt/Fe ECC nanodots, the magnetization gradually reversed from the out-of-plane direction towards the in-plane direction before switching to the reverse out-of-plane direction. The critical size of single magnetic domains in the FePt/Fe ECC nanodots increased with increasing Fe soft layer thickness.

Settlement prediction and behaviour of pile foundations in deep clayey soil deposits

A new measurement technique is used to determine the settlement of bridge pile foundation and the thickness of deep compressed soft layer. The finite element Plaxis 3D foundation program is used in the analysis with a proposed empirical equation to modify the input parameters represented by the soil compression modulus. The results of the numerical analysis using the proposed empirical equation provide insight to the settlement analysis of pile groups in soft clayey soils; consequently, the finite element Plaxis 3D program can be a useful tool for numerical analysis. The numerical analysis is modified by adjusting the calculation of compression modulus from those obtained under pressure between 100–200 kPa by which the results of the settlement are modified and thus matching the realistic measurements. The absolute error is 3 mm which is accepted compared with the last researches. This scenario can be applied for the similar problems in the theoretical applications of deep foundations.

Inclusion of surface anisotropy in the micromagnetic analysis of exchange-coupled hard/soft bilayers

The effects of surface anisotropy and interface anisotropy in soft and hard layers have been considered in the frame of a previously developed micromagnetic continuum model for the study of demagnetization processes in exchange-coupled bi- and multi-layers of soft/hard-type with planar and perpendicular anisotropy, in order to extend and generalize it. In particular, fields applied along the easy direction and strong interface ferromagnetic coupling have been considered. The theoretical results have been applied to a bilayer with perpendicular anisotropy in the hard layer and positive perpendicular surface anisotropy in the soft layer, in order to compare them with those obtained by considering the equivalent volume anisotropy in the soft layer. Moreover, the separate effects of positive perpendicular surface and interface anisotropies in the bilayer have been compared. We have deduced the nucleation field equation and obtained plots of the nucleation field as a function of the soft layer thickness and of the surface and interface anisotropies. Demagnetization curves have been also calculated. The nucleation process can be reversible (exchange-spring (ES) regime) or irreversible (rigid magnet (RM) regime) depending on magnetic and geometrical parameters. The critical equation, which allows determining the boundary between RM and ES regions, has been deduced. Corresponding phase diagrams in the plane of soft and hard layer thickness have been obtained as a function of surface and interface anisotropies.

Zero discharge fluid dynamic gauging for studying the thickness of soft solid layers

Fluid dynamic gauging (FDG) is an experimental technique for measuring the thickness and strength of solid layers on solid or porous substrates by relating the flow rate of liquid through a nozzle positioned near to, but not touching, the layer. This paper shows that such measurements can be made with the liquid both being ejected from and sucked into the nozzle, so that there is no net flow of liquid into or out of the system. This zero discharge (ZFDG) mode has considerable potential for sterile and aseptic operation. Discharge coefficient profiles are reported for a range of flow rates and show very good agreement with computational fluid dynamics simulations, indicating that the shear stress imposed on the surface can be estimated with confidence. The use of ZFDG to study the thickness and removal of soft layers was demonstrated with layers of a commercial petroleum jelly (Vaseline®) layer. The Vaseline® layers exhibited cohesive breakdown on 316 stainless steel, indium tin oxide coated polyethylene terephthalate (PET), and glass under suction mode testing. The cohesive strength agreed with the yield stress measured in separate rheological tests. When exposed to ejecting liquid on glass, however, the layers switched from cohesive breakdown to an adhesive rupture mechanism which is attributed to an instability in the layer and the observed tendency to slip on smooth substrates.

Thermal Stability of FePt-Based Exchange Coupled Composite Films

Three series of L10-FePt based exchange coupled composite (ECC) films L10-FePt/Fe, L10-FePt/[Co/Ni]N and L10-FePt/[Co/Pt]N, with different magnetization configurations, on MgO substrates are studied. Though all series of samples show similar dependences of coercivity on the soft layer thickness, their thermal stabilities are much different. The perpendicular ECC film of L10-FePt/[Co/Ni]N shows a higher thermal stability than that of in-plane one of L10-FePt/Fe for all the soft layer thicknesses.

Structural and magnetic properties of L10-FePt/Fe exchange coupled nano-composite thin films with high energy product

Nanoparticle-FePt/Fe bilayer thin films with different Fe layer thicknesses and [nanoparticle-FePt/Fe]n multilayer thin films with various periods were fabricated by DC magnetron sputtering. Their structures and magnetic properties (energy product and exchange coupling) were investigated by X-ray diffraction technique and vibrating sample magnetometer, respectively. The results show that coercivities of FePt/Fe bilayer films are dropped from 10.7kOe to 0.53kOe with increasing Fe soft magnetic layer thickness, due to the interconnecting of FePt nano-particles by Fe-rich soft magnetic phase and decreasing of the ordering degree of L10-FePt phase. The critical Fe layer thickness changing the annealed film from granular to continuous microstructure is about 4nm. For multilayer [FePt/Fe]n films, both ordering degree of L10-FePt phase and magnetic properties are improved with the number of layer periods. Moreover, a maximum energy products as high as 21.65MGOe is obtained in the [FePt/Fe]5 multilayer film. The enhancement of saturation magnetization and energy products can be ascribed to the high ordering degree of FePt phase as well as the strong exchange coupling among L10-FePt hard magnetic phase and Fe-rich soft magnetic phase.

Effect of the Thickness and Position of Soft Layers in Composite Laminates on the Bending Stiffness

This study investigates the effect of a soft layer integrated in a composite laminate on its mechanical properties through a parametric study. The parameters include the thickness and material properties of such a layer and its placement within the laminate. The numerical evaluations are performed with the finite element method. The necessary mesh density is found by using Pagano’s exact solution for model verification.

3D and 1D calculation of hysteresis loops and energy products for anisotropic nanocomposite films with perpendicular anisotropy

In this paper, the magnetic reversal process, hysteresis loops and energy products for exchange-coupled Nd2Fe14B/α-Fe bilayers are studied systematically by a three-dimensional (3D) model. The 3D calculations are numerically solved using the finite difference method, where the results are carefully compared with those calculated by one-dimensional (1D) model. It is found that the calculated hysteresis loops and energy products based on the two methods are consistent with each other. Both nucleation fields and coercivities decrease monotonically as the soft layer thickness Ls increases. In addition, the calculated spatial distributions of magnetization orientations in the thickness direction at various applied fields based on both methods signify a three-step magnetic reversal process, which are nucleation, growth and displacement of the domain wall. The calculated magnetic orientations within the film plane, however, are totally different according to the two methods. The 3D calculation exhibits a process of vortex formation and annihilation. On the other hand, the 1D calculation gives a quasi-coherent one, where magnetization orientation is coherent in the film plane and varies in the thickness direction. This new reversal mechanism displayed in the film plane has a systematic influence on the nucleation fields, coercivity and energy products.

A fluid dynamic gauging device for measuring fouling deposit thickness in opaque liquids at elevated temperature and pressure

We report proof-of-concept results for a fluid dynamic gauging (FDG) device for measuring the thickness and strength of soft solid fouling layers immersed in an opaque liquid in situ and in real time at elevated pressures and temperatures. The device reported here is configured to make measurements on the inner rod of an annular flow test section but the concept is generic. Data are presented from tests using mineral oil at temperatures and pressures up to 140°C and 10bara, respectively. Problems with the prototype hardware prevented testing up to the design limits of 270°C and 30bara. The practical working range of the gauge, i.e. 0.05<h/dt<0.25, proved to be unaffected by the pressure and temperature. h is the nozzle-surface clearance and dt the nozzle throat diameter. At smaller h/dt values the pressure drop across the nozzle is very high and this can serve as an alarm for close approach. When the Reynolds number at the throat, Ret, is less than 20 the range of discharge coefficient values (0-Cd∞) is small, with a maximum value dependent on Ret. A useful range of Cd∞ values is obtained when Ret>40. Computational fluid dynamics (CFD) simulations of the gauging flow in these quasi-static experiments (no bulk liquid flow) gave good agreement with experimental data for the cases tested. The CFD results showed that the low Ret regime is related to creeping flow in the nozzle. CFD calculations of the shear stress being imposed on the surface being gauged gave good agreement with an analytical model for flow between parallel discs, indicating that the latter can be used to estimate the maximum shear stress imposed by the gauging flow.

Energy barrier measurement and optimization in exchange coupled FePt/TiO2 nano-composite thin films

The 45-degree method is firstly applied to measure the energy barrier of FePt/TiO2 nanocomposite thin films with hard layer only and with hard–soft coupled bilayers. It was experimentally demonstrated that energy barrier measured using 45-degree method is more reliable than that measured using the conventional method with which the field is applied along the film normal. It is found that the energy barrier of bilayer films decreases with soft layer thickness, while the interlayer exchange coupling has little effects on the energy barrier. Both soft layer thickness and interlayer coupling strength have a strong effect on the figure of merit. Decrease in interlayer coupling firstly increases the figure of merit, while, too much reduction of coupling results in the appearance of 2-step switching and therefore decreasing in figure of merit.

Modeling Exchange—Spring Layered Systems With Perpendicular Anisotropy Using Ferromagnetic Resonance Measurements

We have experimentally studied the FePt/Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Pt bilayer system using ferromagnetic resonance at room temperature. Measurements were taken as a function of the direction of the applied external magnetic field with respect to the sample plane. Results show that the effect of exchange coupling is manifest by the induction of a strong perpendicular anisotropy into the soft layer (Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Pt) from the hard layer (FePt). We have used the angular variation of the resonance field to allow us to assess the anisotropy constants for three different thicknesses of the soft layer (2, 3.5 and 5 nm). We observe a decrease of the overall perpendicular anisotropy as the soft layer thickness increases. We note that the hard layer does not contribute to the spectra under the experimental conditions used (9.3 GHz, magnetic fields up to 1 T). We have modeled the bilayer system using the free energy of the system, which includes the effective anisotropies of the layers. In order to fully appreciate the effects of exchange coupling, we have used previously published data of the spin orientation in the soft layer to assess the most appropriate values of the anisotropy constants for the FePt/Fe system. The results indicate that the best way to model these hard-soft coupled ferromagnetic layers is by using a variable effective anisotropy constant in the soft layer, from which almost exact solutions can be obtained. Averaging the anisotropy over the entire layer gives a good measure of the effective anisotropy and the thickness dependence of the effective anisotropy agrees very well with that found experimentally using ferromagnetic resonance.

Study on Post-Construction Settlement of Ningbo Airport Runways

Built on soft soil foundation, the runways settlement of Ningbo Airport has been observed since operation. Through observations respectively after one and nine years in service, we find that the post-construction settlement is directly related to the soft layer thickness and the sand drain depth; meanwhile the accumulated impact caused by landings of aircrafts is yet another factor which cannot be neglected. Post-construction settlement mostly occurs in the initial operation stage of the airport. The maximum cumulative post-construction settlement is 12.95cm one year after operation and increases to 23.70cm nine years after, which is far beyond the design value 8cm. The differential settlement is less than 4cm one year after operation, and stays below 4cm nine years after except for a few points, which basically meets the design requirements.

Structural and magnetic properties of L10/A1, FePt nanocomposites

In this work structural and magnetic properties of (L10-FePt/A1-FePt) exchange coupled nanocomposites are presented. Semi spherical “dome-like” nanocomposites with L10 FePt isolated nanoparticles and A1 FePt (fcc) cap layers were obtained by depositing A1-FePt on type L10 FePt nanoparticles in order to understand the influence of the soft magnetic layer thickness on the magnetic properties of the system. Epitaxial growth is confirmed by X-ray diffraction and TEM, while the coercivity decreases dramatically for the L10/A1-FePt system when the thickness of the A1-FePt cap layers is increased. This result can be used to realize ultrahigh magnetic recording media with tunable coercivity, suitable for conventional write heads.

3D and 1D micromagnetic calculation for hard/soft bilayers with in-plane easy axes

Macroscopic hysteresis loops and microscopic magnetic moment distributions have been determined by three-dimensional (3D) as well as one-dimensional (1D) micromagnetic models for exchange-coupled Nd2Fe14B/α–Fe bilayers and carefully compared with each other. It is found that the results obtained from the two methods are consistent with each other, where the nucleation and coercive fields decrease monotonically as the soft layer thickness Ls increases whilst the largest maximum energy products (roughly 600kJ/m3) occur at Ls=5nm. Moreover, the calculated angular distributions in the thickness direction for the magnetic moments are similar. Nevertheless, the calculated critical fields and energy products by 3D OOMMF are systematically smaller than those given by the 1D model, mainly due to the local demagnetization fields, which are taken into account in the 3D calculation and ignored in the 1D calculation. It is demonstrated by the 3D calculation that the large demagnetization fields in the corners of the soft layers reduce the nucleation fields and thus facilitate the magnetic reversal. Such an effect enhances as Ls increases. When Ls=20nm, the differences between the coercivity is as large as 30%, while the nucleation fields obtained by the two methods have opposite signs.

Polarization of a Diffuse Soft Particle Subjected to an Alternating Current Field

The polarization of a diffuse soft particle submerged in an aqueous electrolyte and subjected to a uniform alternating electric field is theoretically analyzed with the standard electrokinetic model (the Poisson-Nernst-Planck equations). The particle consists of a rigid uncharged core and a charged diffuse polyelectrolytic shell (soft layer) permeable to ions and solvent. Our focus is on the impact of the characteristics of the soft layer including the Donnan potential, the soft layer thickness, and the friction coefficient of the soft layer on the dipole coefficient, characterizing the strength of the polarization. Under the limits of thin double layers and thin polyelectrolytic shells, approximate analytical expressions to evaluate the dipole moment coefficients are derived for high-frequency and low-frequency ranges, respectively. The analytical results are compared and agree favorably with those numerically computed by the standard model. Interestingly, we discover that when the double layer is comparable to the soft layer the dipole moment behaves qualitatively differently at different Donnan potentials. When the Donnan potential is small, the dipole moment decreases as the double layer increases. In contrast, at large Donnan potentials, the dipole moment increases with the increase in the double layer. The distinct responses to Donnan potentials are attributed to the impact of the associated double layer on the charge distribution of mobile ions inside the soft layer. The theoretical model provides a fundamental basis for interpreting the polarization of heterogeneous systems, including environmental or biological colloids or microgel particles.

Magnetization reversal mechanism in perpendicular exchange-coupled Fe/L10–FePt bilayers

The magnetization reversal mechanism in perpendicular soft/hard Fe/FePt exchange-coupled bilayers has been investigated as a function of the soft layer thickness (tFe = 2, 3.5, 5 nm) combining magnetization loops at variable angle, magnetic domain analysis by magnetic force microscopy and numerical micromagnetic simulations. The analytical model proposed in the literature can properly account for some features of the reversal mechanism, such as positive nucleation fields and the reduction of the perpendicular coercive field and remanence by increasing the soft layer thickness, but cannot satisfactorily describe the magnetization process of real systems. We showed that for a thickness of the soft layer exceeding the FePt exchange length (∼2 nm), numerical micromagnetic calculations are needed to reproduce experimental observations. Indeed, just above the coercive field, the magnetization reversal does not proceed in single step switching, as predicted by the analytical model, but according to a more complex process: evolution of nucleated magnetic domains whose magnetization is approximately along the surface normal in the hard layer and slightly out of the film plane in the soft layer, followed by rotation of Fe moments along the field direction.