Magnetic Viscosity Measurements Research Articles

Angular dependence of the magnetization relaxation in Co/Pt multilayers

We study the influence of defects in Co/Pt multilayers on the room-temperature magnetization reversal and relaxation mechanisms via angle-dependent magnetic viscosity and coercive field measurements. The data reveal a transition from pinning-dominated domain wall propagation to a sequence of pinning-dominated and uniform switching, with increasing tilt away from the normal direction. The leading role of the dendritic domain wall propagation in the nanogranular exchange-coupled films is corroborated by the scaling of relaxation times, the angular dependence of the coercive field, and Kerr microscopy.

Bio-Based Epoxy Adhesives with Lignin-Based Aromatic Monophenols Replacing Bisphenol A.

A bio-epoxy surface adhesive for adherence of the metal component species to glass substrate with desirable adhesion strength, converted controlled removal upon request, and bio-based resource inclusion was developed. For the development of resin, three different lignin-based aromatic monophenols, guaiacol, cresol, and vanillin, were used in the chemical epoxidation reaction with epichlorohydrin. The forming transformation process was studied by viscoelasticity, in situ FTIR monitoring, and Raman. Unlike other hydroxyl phenyls, guaiacol showed successful epoxide production, and stability at room temperature. Optimization of epoxide synthesis was conducted by varying NaOH concentration or reaction time. The obtained product was characterized by nuclear magnetic resonance and viscosity measurements. For the production of adhesive, environmentally problematic bisphenol A (BPA) epoxy was partially substituted with the environmentally acceptable, optimized guaiacol-based epoxy at 20, 50, and 80 wt.%. Mechanics, rheological properties, and the possibility of adhered phase de-application were assessed on the bio-substitutes and compared to commercially available polyepoxides or polyurethanes. Considering our aim, the sample composed of 80 wt.% bio-based epoxy/20 wt.% BPA thermoset was demonstrated to be the most suitable among those analyzed, as it was characterized by low BPA, desired boundary area and recoverability using a 10 wt.% acetic acid solution under ultrasound.

Coercivity analysis of cubic and tetragonal (Cu,Co) ferrite particles within the global model

We analyzed the coercivity of both cubic and tetragonally distorted Co x Cu1−x Fe2O4 particles (x = 0.2 and 0.1, respectively) using the global model. According to magnetic viscosity measurements, the size of the activation volumes v a increases from around 2000 nm3 (v a 1/3 ≈ 13 nm) at 10 K for both samples, to close to 175 000 nm3 for the cubic sample and 5400 nm3 for the tetragonally distorted sample at 300 K. The microstructure-related phenomenological parameters obtained from the global model analysis are α= 0.29 and N eff = −0.01 and α= 0.39 and N eff = −0.24 for the cubic and tetragonal samples, respectively. High-resolution transmission electron microscopy images of the tetragonal sample showed that nanograins are connected through a thin amorphous layer (∼1 nm), which could account for the intergranular exchange interactions indicated by the negative value of N eff as well as values of M r/M s > 0.5 for such isotropic samples. Low temperature discrepancies are tentatively attributed to magnetic reversal being governed by a local heating process following thermal activation.

Coercivity Analysis and Magnetization Reversal Mechanism in Permanent Magnets

During the last decade, coercivity enhancement of permanent magnets has been one of the major issues due to the strong demands of high-performance magnets for the traction motors of electric/hybrid vehicles. For this purpose, the study on the coercivity mechanism of permanent magnets is essentially important. However, this has been uncleared regardless of the past long-discussed studies. Recently, we have tacked this issue using the multi-scale coercivity analysis. As macroscopic coercivity analyses, two different approaches were employed. One was the first-order reversal curve (FORC) analysis, which revealed the dominant magnetization reversal process, i.e., single- or multi-domain magnetization reversal. The other was the energy barrier analysis based on the magnetic viscosity measurements. On the other hand, as a microscopic coercivity analysis, an elemental-magnetization reversal measurement was attempted. In this paper, these multi-scale coercivity analyses have been reviewed.

Nuclear magnetic resonance spin-lattice relaxation of lithium ions in aqueous solution by NMR and molecular dynamics.

We study the aqueous solvation dynamics of lithium ions using nuclear magnetic resonance spectroscopy, molecular dynamics, and viscosity measurements. Several relaxation mechanisms are examined to explain the strong increases of spin-lattice relaxation toward high concentrations. The use of both 6Li and 7Li isotopes is helpful to identify the quadrupolar contribution to the relaxation rate. In particular, it is found that the quadrupolar interaction constitutes the strongest contribution above a concentration of ∼10 molal. The next-strongest contribution arises from interactions that scale with the square of the gyromagnetic ratio (mostly the dipolar interaction), and the experimental relaxation rates appear to be fully accounted for when these mechanisms are combined over the concentration range up to the saturation concentration. The study of solvation dynamics, particularly at high concentrations, could be of relevance for electrolyte dynamics in aqueous Li-ion rechargeable batteries.

Enhancing the Corrosion Protection of AA2024-T3 Alloy by Surface Treatments Based on Piperazine-Modified Hybrid Sol–Gel Films

The aim of this study was to develop new chrome-free surface pretreatments for AA2024-T3 aluminum alloy. These pretreatments were based on hybrid organic–inorganic sol–gel thin films prepared from mixtures of γ-methacryloxypropyltrimethoxysilane (MAPTMS) and tetramethylorthosilicate (TMOS). Different MAPTMS/TMOS molar ratios were used for optimizing the physical–chemical characteristics of the sol–gel films. The formulation of a set of these sols was modified by incorporating piperazine (1,4-diazacyclohexane) as a corrosion inhibitor. The resulting sol–gel films were characterized by using Fourier transform infrared spectroscopy (FTIR), liquid-state 29Si nuclear magnetic resonance spectroscopy (29Si-NMR) and viscosity measurements. The corrosion performance of the sol–gel films was analyzed by using electrochemical impedance spectroscopy (EIS) and local electrochemical impedance mapping (LEIM). The characterization techniques indicated that piperazine behaved as a catalyst for the condensation reaction during the formation of the MAPTMS/TMOS organopolysiloxane network and produces an increase of the crosslinking degree of the sol–gel films. EIS and LEIM results showed that piperazine is an effective corrosion inhibitor, which can be used to enhance the active corrosion protection performance of sol–gel films.

1H-NMR and viscosity studies of hydrogen bonding of Chinese rice wine

ABSTRACTThe viscosity of Chinese rice wine gradually increases with the maturing process, resulting in a better taste due to longer contact with the tongue. Herein, the structure of water–ethanol was detected by hydrogen nuclear magnetic resonance (1H-NMR) and viscosity measurement to define the strength of hydrogen bonding. Through single-factor experiments, it can be seen that most of the flavors have a promoting effect on alcohol–water hydrogen bonding, with the exception of aldehydes. And the factors influencing hydrogen bonding in decreasing order were determined by Plackett–Burman (PB) test. The relationship between hydrogen bonding strength and flavor in Chinese rice wine with 18% (v/v) alcohol concentration was investigated through multiple regression analysis, with an adjusted R2 of 0.925. The results of study provide important insight for the quality control and molecular mechanism of viscosity increasing during Chinese rice wine aging.

Improved Corrosion Resistance of AA2024 Alloys through Hybrid Organic-Inorganic Sol-Gel Films Modified with Piperazine

Hybrid sol-gel coatings were prepared by using mixtures of γ-methacryloxypropyltrimethoxysilane (MAPTMS) and tetramethylorthosilicate (TMOS) as organopolysiloxane precursors and piperazine as a corrosion inhibitor [1]. The sol-gel films were characterized by using Fourier transform infrared spectroscopy (FTIR), liquid state Si liquid-state nuclear magnetic resonance spectroscopy (29Si NMR) and viscosity measurements. The corrosion performance of the resulting coatings was analysed by using Global and Local Electrochemical Impedance Spectroscopies (EIS, LEIS). The study shows that these new coatings have promising anticorrosive properties when they are used for the corrosion protection of AA2024-T3 alloys in contact with NaCl aqueous solution. The incorporation of piperazine additionally results in more effective barrier proprieties and improved corrosion protection of AA2024-T3 alloys acting firstly as a catalyst for Si-OH condensation during the polymerization of the organopolysiloxane network increasing film thickness and secondly as a metal corrosion inhibitor of the metal substrate in the base of pores of the sol-gel film. Acknowledges: This work was supported by the Ministry of Economy and Competitiveness of Spain (Project MAT2015-65445-C2-1-R) and Comunidad de Madrid (Project S2013/MIT-2862-MULTIMAT-CHALLENGE). References D.J. Carbonell, A. García-Casas, J. Izquierdo, R.M. Souto, J.C., Galván, A. Jiménez-Morales, Scanning electrochemical microscopy characterization of sol-gel coatings applied on AA2024 substrate for corrosion protection, Corrosion Science, 111 (2016) 625–636.

Coercivity global model and magnetization reversal in fine hexaferrites

In this work, the so‐called global model for magnetization reversal is applied to describe the coercive field temperature dependence in fine barium and strontium M‐hexaferrites (75–300 K range). Using magnetic viscosity measurements, the temperature dependence of the activation volume for magnetization reversal was obtained. In this temperature range, the coercive field (as the anisotropy field) increases with increasing temperature. However, it is found experimentally that the activation volume also increases with temperature and then the physical interpretation of the model is partially not clear.

Temperature-dependent magnetization reversal process and coercivity mechanism in Nd-Fe-B hot-deformed magnets

Low coercivity and its large temperature dependence of a Nd2Fe14B magnet with respect to its magnetic anisotropy field have been addressed as the coercivity problem. To elucidate the physical origin of this problem, we have investigated the temperature dependence of the magnetization reversal behavior in the Nd-Fe-B hot-deformed magnet. Based on the analysis of the energy barrier evaluated from magnetic viscosity measurements, the coercivity problem is discussed in terms of the following three aspects: magnetization reversal process, intrinsic coercivity without thermal demagnetization effect, and energy barrier height. The analyses lead us to conclude that domain wall pinning is dominant in the magnetization reversal in the Nd-Fe-B hot-deformed magnet. The temperature dependences of the intrinsic coercivity and the energy barrier height are explained by the grain boundary model with an intermediate layer. These analyses would be utilized to discuss the detailed structure and magnetic properties of the grain boundary, which gives a new insight to overcome the coercivity problem.

Determining the magnetic attempt time τ0, its temperature dependence, and the grain size distribution from magnetic viscosity measurements

AbstractA new method to determine the atomic attempt time τ0 of magnetic relaxation of fine particles, which is central to rock and soil magnetism and paleomagnetic recording theory, is presented, including the determination of its temperature dependence, and simultaneously the grain size distribution of a sample. It is based on measuring a series of zero‐field magnetic viscous decay curves for saturation isothermal remanent magnetization at various different temperatures that are later joined together on a single grain size scale from which the grain size distribution and attempt time are determined. The attempt time was determined for three samples containing noninteracting, single‐domain titanomagnetites of different grain sizes for temperatures between 27 K and 374 K. No clear temperature‐dependent trend was found; however, values varied significantly from one sample to the other: from 10−11 to 10−8s; in particular, the sample containing multiple magnetic phases had an effective attempt time significantly lower than the more homogeneous samples, thereby questioning the applicability of the simple Néel‐Arhennius equation for magnetic relaxation for composite materials.

Energy barrier analysis of Nd-Fe-B thin films

The magnetization reversal mechanism of a permanent magnet has long been a controversial issue, which is closely related to the so-called coercivity problem. It is well known that the energy barrier for magnetization reversal contains essential information on reversal process. In this study, we propose a method to analyze the energy barrier function for the magnetization reversal. Preferentially (001) oriented Nd-Fe-B films with and without a Nd overlayer are used as model magnets. By combining the magnetic viscosity and time dependent coercivity measurements, the barrier function has been successfully evaluated. As a result, although the Nd-Fe-B films with and without Nd overlayer exhibit different magnetic behaviors, the power indices for their energy barrier are almost the same, suggesting that the magnetization reversal proceeds in a similar mode.

Thermosets from highly functional methacrylated epoxidized sucrose soyate

Highly functional biobased methacrylate oligomers were synthesized via the reaction between methacrylic acid and epoxidized sucrose soyate (ESS); then, biobased thermosets were produced from free-radical curing of these methacrylates using styrene as a reactive diluent. The methacrylated ESS resins (MESSs) were characterized using gel permeation chromatography, Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance spectroscopy and viscosity measurements. MESS were mixed with styrene at different ratios and cured by free-radical polymerization using peroxides as the initiators to form thermosets. The extent of cure was confirmed by FTIR and gel content determinations. The properties of the thermosets were studied using tensile testing, dynamic mechanical thermal analysis and thermogravimetric analysis. Compared to their counterparts based on a reference, methacrylated epoxidized soybean oil, thermosets based on MESS showed much higher glass transition temperature (Tg) and better mechanical properties, which can be attributed to the unique combination of high methacrylate functionality and the rigid sucrose core in the MESS oligomers.

Dynamics of methanol in ionic liquids: validity of the Stokes-Einstein and Stokes-Einstein-Debye relations.

The validity of Stokes-Einstein (SE) and Stokes-Einstein-Debye (SED) relations for methanol in the physical environment of the ionic liquid (IL) 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide is studied by means of nuclear magnetic resonance (NMR) relaxation time experiments, viscosity measurements and molecular dynamics (MD) simulations. The reorientational correlation times of the hydroxyl groups of pure methanol and of methanol in the IL/methanol mixtures were determined. For that purpose an approach for estimating NMR deuteron quadrupole coupling constants, presented by Wendt and Farrar (Mol. Phys. 1998, 95, 1077-1081), was confirmed. The self-diffusion coefficients of methanol were taken from the MD simulations. The viscosities of all systems were then measured and the SE and SED relations validated. For pure methanol both relations are valid, whereas they become increasingly invalid with increasing IL concentration, as indicated by effective volumes and radii that are too low. The deviation from the SE and SED relations could be related to dynamical heterogeneities described by the non-Gaussian parameter α(t) obtained from MD simulations. For pure methanol, α(t) is close to zero in accord with the validity of both relations. With increasing IL concentration the dynamical heterogeneities of methanol increase strongly. The times t* at the maximum of α(t) increase linearly with the relative number of methanol monomers in the mixtures. Thus, the dynamical heterogeneities are largest for single methanol molecules fully embedded in the IL environment. In their own environment methanol molecules are highly mobile, whereas in the IL-rich region the mobility is strongly reduced leading to the non-validity of SE and SED relations.

Removal of Hg0 from flue gas using Fe-based ionic liquid

Abstract Fe-based alkylimidazolium halide ionic liquids ([bmim]·FeXCl 3 , X = Cl and Br) were prepared by a two-step reaction. And then the ionic liquids were characterized by infrared spectroscopy, Raman spectroscopy, nuclear magnetic resonance, thermogravimetric analysis and viscosity measurements. The Hg 0 removal performance of the ionic liquid was also investigated in a gas/liquid scrubber using simulated flue gas. It was found that the ionic liquid possessed low viscosity and high thermal stability, and could be used as an absorbent for Hg 0 removal from the flue gas. The ionic liquid showed high Hg 0 removal efficiency (up to 98%) in the temperature range of 60–100 °C. The Hg 0 removal mechanism involved with Hg 0 oxidation by the anion of ionic liquid and the regeneration of the anion.

Demonstration of the thermal stability advantage of advanced exchange coupled composite media

We systematically vary the strength of the vertical interlayer exchange coupling (VIEC) between the magnetic layers (MLs) of an advanced exchange coupled composite media and experimentally investigate, through magnetic viscosity and dynamic coercivity measurements, the impact on the thermal stability. The strength of the VIEC is controlled through exchange coupling layers of varied thicknesses, whereas MLs are unchanged. We estimate the thermal energy barrier ΔEo as a function of the VIEC within the standard Arrhenius-Neel relaxation and Sharrock formalisms and characterize the effect of the VIEC on the degree of incoherency in the grain reversal mechanism. The analysis shows that while ΔEo drops for weaker VIEC, the ratio of ΔEo to MsHo energy per activation volume is maintained near 2 and weakly optimizes for intermediate VIEC.

Correlation between magnetic interactions and domain structure in A1 FePt ferromagnetic thin films

We have investigated the relationship between the domain structure and the magnetic interactions in a series of FePt ferromagnetic thin films of varying thickness. As-made films grow in the magnetically soft and chemically disordered A1 phase that may have two distinct domain structures. Above a critical thickness dcr ∼ 30 nm the presence of an out of plane anisotropy induces the formation of stripes, while for d < dcr planar domains occur. Magnetic interactions have been characterized using the well known DC demagnetization - isothermal remanent magnetization remanence protocols, δM plots, and magnetic viscosity measurements. We have observed a strong correlation between the domain configuration and the sign of the magnetic interactions. Planar domains are associated with positive exchange-like interactions, while stripe domains have a strong negative dipolar-like contribution. In this last case we have found a close correlation between the interaction parameter and the surface dipolar energy of the stripe domain structure. Using time dependent magnetic viscosity measurements, we have also estimated an average activation volume for magnetic reversal, ⟨Vac⟩∼1.37×104 nm3, which is approximately independent of the film thickness or the stripe period.

Study on the magnetic viscosity of Nd45Pr15Fe30−xCoxAl10 (x=0, 10) bulk amorphous Alloys

The bulk amorphous Nd45Pr15Fe30−xCoxAl10 (x=0, 10) alloys, which were prepared by arc melting and investigated by XRD and VSM, present hard magnetic behavior at room temperature. The intrinsic coercivity of the bulk amorphous increased with increasing Co addition. A single sharp and narrow peak close to the coercivity appeared in the irreversible susceptibility (χirr) curve for each alloy. The addition of Co has little influence on the magnetic viscosity of the alloys. With the substitution of Co for Fe, the fluctuation field Hf increased from 9.9mT to 11.5mT, and the activation volume Va increased from 2.9×10–18cm3 to 3.6×10–18cm3, which leads to an increase of the activation diameter Da from 17.7nm to 19.0nm. The value of Da deduced from the magnetic viscosity measurements is similar to the size of clusters of Nd-based bulk amorphous alloys, which may be responsible for the hard magnetic property exhibited at room temperature.

Supramolecular Phosphorescent Polymer Iridium Complexes for High-Efficiency Organic Light-Emitting Diodes

The synthesis of supramolecualr phosphorescent polymers (SPPs) as a novel class of solution-processable electroluminescent (EL) emitters was presented. The SPPs were formed by utilizing the efficient nonbonding self-assembly of luminescent iridium monomer 1 and “terfluorenyl”-based monomers 2 and 3, tethered with either a crown ether or dibenzylammonium unit. The supramolecular assembly process was monitored and illustrated by 1H nuclear magnetic resonance (NMR) and viscosity measurement. Moreover, the SPPs exhibit an intrinsic glass transition with a glass-transition temperature (Tg) of 72.5–81.5 °C, which is absent in the monomers. The characterization of organic light-emitting diodes that consisted of these SPPs as an emitter gave an efficiency of 14.6 cd A–1 at a luminance of 450 cd m–2. Considering the good solution processability and catalyst-free polymerization process for the designed SPPs, combining the good device performances, the present study provide a promising alternative route to develop s...

Application of Magnetic Field Method for Measuring Lubricant Viscosity

This study presents an application of Hall Effect sensor to assess the viscosity of industrial lubricant by using reference metal particles with the dimension ranging from 1 µm to 100 µm and the mass ranging from 0.1 g to 1 g as the essential modules of the developed system. Hall Effect sensor is a small electronic component which is easy for installing, analyzing, and processing due to electrical output generated. Moreover, the cost of this developed method is lower than other means of viscosity tests. At present, there are several studies on viscosity and quality tests of industrial lubricants such as Ultrasonic measurement of viscosity of liquids [1], Photoacoustic measurement of liquid viscosity [2], Measurement of magnetic viscosity in NdFeB [3], A viscosity and density meter with a magnetically suspended rotor [4], Capacitive sensor [5], IR-Absorption [6], and Optical fiber sensing [7]. In this study, the measurement methodology was considered only the lubricant viscosity at the temperature of 26 °C and then compared the results to the viscosity classification which is the reference of lubricant characteristic. Moreover, the lubricant types namely SAE 15W-40, SAE 20W-50 and ISO VG 100 were selected as the case studies.