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We present a study of the properties related to the magnetization reversal process in two thin-film samples with magnetic stripe domains: Fe0.82Ga0.18 (Fe–Ga) and Ni0.81Fe0.19 (permalloy). In Fe–Ga thin films, we focus on magnetization reversal driven by thermal activation by considering the magnetic viscosity behavior. The results suggest that the reversal process occurs gradually, where the magnetization switches direction via ∼ 10 nm-long jumps of the magnetic domain walls. On the other hand, vectorial hysteresis loops were performed in permalloy thin films with the aim to study the behavior of the transverse magnetization component (perpendicular to the applied field) during the magnetization reversal process. We show that the measurement of the transversal magnetization component shows a much higher sensitivity for the determination of the in-plane magnetic anisotropy than the usual hysteresis loops where the magnetization is parallel to the applied field. Moreover, this allows to highlight the competition between the intrinsic and rotatable anisotropies in thin films that present stripe domains. [ABSTRACT FROM AUTHOR]

The effect of MHD flow of viscous, incompressible fluid with small electrical conductivity past an infinitely long perfectly conducting porous plate started impulsively from rest in the presence of a constant transverse magnetic field fixed relative to the fluid is investigated. We also imposed a small uniform suction or injection at the plate. Skin friction at the plate, non-dimensional forms of the velocity, and the induced magnetic field have been obtained. The graphs of velocity and magnetic field are also drawn for various values of suction, and magnetic parameters are clearly explained. From the investigations, it is found that the fluid velocity decreases due to the increasing value of kinematic viscosity and constant suction velocity. It also finds that the induced magnetic field increases due to constant suction velocity. [ABSTRACT FROM AUTHOR]

Results are presented from studying magnetization and remagnetization in single-crystal samples of GdCo4Cu alloy. The coexistence of two hysteresis mechanisms is observed, depending on the magnetic background. Abrupt remagnetization is observed along with strong magnetic viscosity. The relationship between hysteresis processes and the structural states of samples is discussed. [ABSTRACT FROM AUTHOR]

The time-dependent decrease of the magnetic polarization of magnet materials in the presence of an opposing field is well known as the magnetic viscosity or magnetic aftereffect. In previous studies, magnetic viscosity was usually measured in fields when in the vicinity of coercivity H cJ , and this was conducted in order to understand the coercivity mechanism in magnetic materials. In this study, the magnetic viscosity of commercial FeNdB magnets is determined at opposing fields weaker than H cJ and at different temperatures in the range from 303 to 433 K (i.e., from 30 to 160 °C) by means of a vibrating sample magnetometer (VSM). As a result, the parameter S v , which describes the magnetic viscosity in the material, was found to increase with increases in the opposing field. Furthermore, both the parameter S v and its dependence on the temperature were found to correlate with the coercivity H cJ of the material. Also, a difference with regard to the parameter S v for the materials measured in this study with similar magnetic properties, but which had undergone different types of processing, could not be found. Knowledge of the field- and temperature-dependent behavior of the magnetic viscosity of FeNdB magnets allows for better estimations over the lifetime of a component under operating conditions with respect to the magnetic losses in FeNdB magnets that are used in electric components. [ABSTRACT FROM AUTHOR]

The multi-step magnetization behavior caused by a variety of microstructures is common in magnetic materials. The study of the effect of heterogeneous structure magnetization behavior on magnetic viscosity provides extensive guidance for the long-term stability of magnetic materials. The microstructure of Fe–Co–Ni–Al–Ti–Cu alloy was regulated by heat treatment process, and homogeneous structure (S810) and heterogeneous structure (S830) samples were prepared. In the S830 sample, there are three steps of magnetization reversal due to the presence of α1′ phases (split α1 phases). Part of the α1′ phases are reversed under a lower magnetic field, and the other part has strong interaction with the α1 phases forming a closed stable magnetic domain structure, which enhances the switch field of α1 phases. Both first-order reversal curves (FORC) analysis and electron holography have confirmed this phenomenon. The magnetic viscosity coefficient of S830 is higher, but its magnetic field dependence is better. The quantitative calculation of energy barriers shows that the energy barriers of α1′ phases are lower, which leads to the instability of S830 sample under low magnetic fields. The superposition of three magnetization reversal steps makes the variation of magnetic viscosity coefficient gentler.

The time-dependent decrease of the magnetic polarization of magnet materials in the presence of an opposing field is well known as the magnetic viscosity or magnetic aftereffect. In previous studies, magnetic viscosity was usually measured in fields when in the vicinity of coercivity HcJ, and this was conducted in order to understand the coercivity mechanism in magnetic materials. In this study, the magnetic viscosity of commercial FeNdB magnets is determined at opposing fields weaker than HcJ and at different temperatures in the range from 303 to 433 K (i.e., from 30 to 160 °C) by means of a vibrating sample magnetometer (VSM). As a result, the parameter Sv, which describes the magnetic viscosity in the material, was found to increase with increases in the opposing field. Furthermore, both the parameter Sv and its dependence on the temperature were found to correlate with the coercivity HcJ of the material. Also, a difference with regard to the parameter Sv for the materials measured in this study with similar magnetic properties, but which had undergone different types of processing, could not be found. Knowledge of the field- and temperature-dependent behavior of the magnetic viscosity of FeNdB magnets allows for better estimations over the lifetime of a component under operating conditions with respect to the magnetic losses in FeNdB magnets that are used in electric components.

Within the theory of random interaction fields, the possibility of determining the Curie point and the paramagnetic Curie point corresponding to the appearance of short-range order is shown. In ferromagnetic alloys, there is a concentration range in which the long-range order is destroyed, but the short-range order persists. This leads to the appearance of a cluster glass phase, which is characterized by a time dependence of the magnetic susceptibility and the appearance of viscous magnetization. For an AuFe alloy as an example, the behavior of the initial magnetic susceptibility as a function of temperature and concentration is studied and compared with experimental data. [ABSTRACT FROM AUTHOR]

Siberian Traps magnetic viscosity affects and makes it difficult to interpret TEM sounding data obtained during oil and gas exploration in the south of the Siberian platform. In this paper, we present and discuss a method for decreasing magnetic viscosity effect on TEM data. The method is based on estimating magnetic viscosity contribution to the total transient response using TEM data measured with multi-offset arrays.

Magnetic viscosity analysis is a widely studied topic in understanding the stability and magnetization mechanisms of magnets. However, observing the minute changes in magnetic domains during the magnetic viscosity process poses a challenge in research. To address this issue, a self-made in-situ magnetized sample holder was used in this study to observe the dynamic evolution of domain structures in alnico alloy during magnetic viscosity. The findings indicate that the domain reversal during magnetic viscosity is largely irreversible, with only minor reversible changes observed in the inhomogeneous region. The magnetization reversal in alnico alloy occurs through the reversal of α1 phases, which follows a single domain particle reversal mode. The zero-field activation energy (E 0) of alnico alloy is determined as 3.30 × 10−17 J, and the coercivity field without thermal disturbance (H 0) is measured at 1779.19 Oe. This research method proves to be a valuable tool in the study of magnetic materials. [Display omitted] [ABSTRACT FROM AUTHOR]

The kinetics of magnetization reversal in a rare-earth-free Mn–Al–C permanent magnet is reported. The $\text{L}1_{0}$ -phase material was prepared using a combination of the melt spinning and spark plasma sintering techniques and characterized with a vibrating sample magnetometer. Magnetic relaxation and susceptibility experiments were performed. Magnetic viscosity, fluctuation field, and activation volume were measured in a wide temperature range. These data were used to analyze the magnetization reversal and temperature dependence of the coercive field. The thermally activated mechanism of the reversed nucleus formation was confirmed for the intermediate temperatures. The role of wall thickness and crystallite size as additional characteristic lengths in magnetic-domain nucleation is discussed. [ABSTRACT FROM AUTHOR]

Purpose. This paper is devoted to investing of the effect of magnetic viscosity on the results of measurements of the main hysteresis characteristics of hard magnetic alloys in an open magnetic circuit of vibrating sample magnetometer.Materials and methods. The studies were performed on a sample of a rapidly quenched nanocrystalline MQP-B+ brand alloy. Hysteresis properties of the alloy in an open magnetic circuit are studied: hysteresis loop, time dependences of magnetization in demagnetizing fields of different intensity, field dependences of the coefficient of magnetic viscosity and irreversible magnetic susceptibility.Results. The dependences of the measurement results of the hysteresis properties on the measurement conditions are established. It is shown that magnetic viscosity must be taken into account when developing hard magnetic reference materials.

Dynamic expressions for bulk and shear viscosity coefficients are obtained on the basis of statistical theory and a model of a two-component system. The dependence of the coefficients of shear viscosity of magnetic fluids based on water, kerosene, and undecane on the frequency and magnitude of an external magnetic field is calculated from the selection of potential energies for intermolecular and dipole–dipole interactions, the radial distribution functions, and the effect of an external magnetic field. The regions of frequency dispersion for the coefficients of shear viscosity of the studied fluids are determined, and the magneto–viscous effect in magnetic fluids is considered. [ABSTRACT FROM AUTHOR]

Magnetic viscosity and interactions have been studied recently in bulk M‐type hexaferrites. Herein, this kind of study is extended to Sr–M (SrFe12O19) thin films deposited on SiO2/Si substrates using the pulsed laser ablation technique at relatively low substrate temperatures at 2.7 mbar oxygen atmosphere. Samples are characterized by X‐ray diffraction, scanning electron microscopy, and vibrating‐sample magnetometry. The high values of the coercive field (4.8 kOe) obtained for the films are in correspondence with large values reported in thin films, powders, and sintered samples for the Sr–M compound. Demagnetization‐like interactions are found and magnetic viscosity results point to the coercivity mechanism different from coherent rotation despite the small particle size. [ABSTRACT FROM AUTHOR]

• Effect of magnetic field intensity during spinodal decomposition on microstructure of alnico magnets. • The randomly oriented a1 phase reduces the decay rate of magnetization. • The main factor affecting the decay rate of magnetization is irreversible magnetic domain reversal. The slow decay of permanent magnet magnetization with storage time will greatly affect the accuracy of precision instruments. The alnico is a traditional permanent magnetic material with excellent stability, and the research on its stability cannot be ignored. Magnetic field heat treatment is a key process that affects the microstructure of the alnico alloy. The alnico alloys with different α1 phase orientations and aspect ratios were prepared by adjusting the magnetic field intensity during spinodal decomposition. With the increase of magnetic field strength, the aspect ratio of the α1 phase increases significantly, and the orientation becomes better, which leads to the increase of coercive force and remanent magnetization, but the magnetic viscosity coefficient decreases. The demagnetization process of alnico samples was characterized by Lorentz transmission electron microscopy (LTEM) and electron holography. At the magnetic field interval of 200 Oe, the area of irreversible magnetization reversal of the S3 is significantly larger than that of the S0. The first-order reversal curves (FORC) show that most the randomly oriented α1 phases are reversible magnetization reversal, and the interaction field is smaller than that of neatly arranged α1 phases. This structure results in better stability. The alnico alloy without a magnetic field during spinodal decomposition sacrifices some magnetic properties but obtains better stability, which provides a research direction for stabilizing treatment by adjusting microstructure. [ABSTRACT FROM AUTHOR]

Purpose. The work is intended to investigate the electromagnetic processes in impedance bond in order to improve noise immunity of track circuits (TC) for safe railway operation. Methodology. To achieve this purpose the methods of scientific analysis, mathematical modelling, experimental study, a large-scale simulation were used. Findings. The work examined the interference affecting the normal performance of track circuits. To a large extent, part of track circuit damages account for failures in track circuit equipment. Track circuit equipment is connected directly to the track line susceptible to traction current interference, which causes changes in its electrical characteristics and electromagnetic properties. Normal operability, performance of the main operating modes of the track circuit is determined by previous calculation of its performance and compilation of regulatory tables. The classical method for determination of track circuit parameters was analysed. The classical calculation method assumes representation of individual sections of the electrical track circuit using the quadripole network with known coefficients, usually in the A-form. Determining the coefficients of linear element circuit creates no metrological or mathematical difficulties. However, in circuits containing nonlinear ferromagnets (FM), obtaining the coefficients on the entire induction change range in the cores is quite a difficult task because the classical methods of idling (I) and short circuit (SC) are not acceptable. This leads to complicated methods for determining both the module and the arguments of quadripole network coefficients. Instead of the classical method, the work proposed the method for calculating the track circuit dependent on nonlinear properties of ferromagnets. Originality. The article examines a new approach to the calculation of TC taking into account the losses in ferromagnets (FM), without determination of equivalent circuit quadripole network coefficients. When building the FM reversal model in parallel magnetic fields, the most accurate methods are the approximation ones that take into account not only the changes in values and over time, but also their derivatives. The development of computer hardware and software makes real the mathematical methods for calculating TC with significant change in ferromagnetic inductance, including the saturation areas. Herewith, it is important to search for approximating analytical expression that describes the dynamic limit hysteresis loop (HL). Practical value. The changes in the electrical parameters of the same TC were analysed using the classical and the new calculation methods, the difference made less than 10%. The work introduced some measures to increase operational noise immunity of TC.

The time, temperature, and magnetic field dependences of the magnetic moment of thin GaMnSb films containing MnSb clusters are measured using a SQUID (superconducting quantum interference device) magnetometer. It is found that magnetic field-induced magnetization reversal and thermally activated spontaneous magnetization reversal in thin GaMnSb films are interrelated as follows: the maximum of the magnetic-field dependence of the magnetic viscosity coincides with the coercive force for the samples. [ABSTRACT FROM AUTHOR]

The magnetic viscosity, S , of Mn-Ga and Mn-Al alloys with the L1 0 type crystal structure has been measured at temperatures in the range 2–300 K. The values of the fluctuation field, S v , and the coercive field, H c , of the two types of materials are comparable to each other. The observed dependence of S v on the applied field, H , is not in accordance with the theory of magnetic viscosity of particulate recording media. The relationship between H c and S v , the latter measured at H = − H c , fits the Barbier relationship, S v ∼ H c α , rather well. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A new method is suggested for calculation of transient electric field response to conducting magnetically viscous earth excited by a grounded line source. Calculation algorithms are implemented in the computer program FwLL_MV. Using a uniform, conducting magnetically viscous half-space as an earth model, we have shown that magnetic relaxation affects the TEM response of equatorial and in-line arrays. As in the case of loop arrays, apparent resistivity steadily decreases with time. The higher the half-space resistivity and the shorter the offset, the earlier the voltage and the apparent resistivity begin to decrease as 1/ t . Magnetic relaxation and decay of eddy currents are independent processes within the range of resistivities typical of rocks. [ABSTRACT FROM AUTHOR]

Noble/transition bimetallic nanowires of nominal composition Fe 90 Rh 10 are AC electrodeposited into 20 nm diameter hexagonally self-assembled alumina nanopores. Nanowires about 18 nm in diameter and 1 μm long are polycrystalline and multiphase. Wires contain α-Fe grains and very small grains of the ClCs-type α′-Fe(Rh) phase. The room temperature magnetization mechanism and the thermal stability of nanowire magnetic configurations are further investigated by measuring the dependence of the coercive field on the applied field sweeping rate R. From these data a mean fluctuations field value of μ 0 H FR = (9.0 ± 0.5) mT is obtained (at coercivity) and an effective activation magnetic moment μ ac = 5400 μ B is estimated, with μ B the Bohr magneton. At the coercive field (about 45 mT) the resulting activation lengths become l AC ≈ 6.4 and 6.7 nm for α-Fe and α′-Fe(Rh), respectively. Assuming an effective magnetic anisotropy, considering magnetostatic shape contributions in addition to the magnetocrystalline one, the domain wall thickness δ w in α-Fe grains and in the α′-Fe(Rh) become δ wFe = 13.4 nm and δ wFeRh = 10.9 nm respectively. These values are comparable to the activation lengths estimated at the coercive field in each phase. These facts strongly indicate that irreversible polarization reversal in these nanowires takes place by local curling, involving localized nucleation modes. [ABSTRACT FROM AUTHOR]

Coercivity and interactions in coprecipitated and ceramic SrFe12O19 (Sr-M) hexaferrite samples were studied using remanence curves and magnetic viscosity in addition to microstructural considerations by means of SEM analysis. Following a magnetic viscosity formalism, the activation volume was obtained and interactions were evaluated using the Δ M technique. Even for a coprecipitated sample with a high coercive field ( Hc = 6100 Oe), the experimental activation volume indicates a non-coherent mechanism for magnetization reversal and demagnetizing-like interactions were found in this isotropic sample with large aspect ratio particles; also demagnetizing-like interactions were found for a thermally treated coprecipitated sample and a ceramic sample. [ABSTRACT FROM AUTHOR]

Coercivity and interactions in coprecipitated and ceramic SrFe12O19 (Sr-M) hexaferrite samples were studied using remanence curves and magnetic viscosity in addition to microstructural considerations by means of SEM analysis. Following a magnetic viscosity formalism, the activation volume was obtained and interactions were evaluated using the Δ M technique. Even for a coprecipitated sample with a high coercive field ( Hc = 6100 Oe), the experimental activation volume indicates a non-coherent mechanism for magnetization reversal and demagnetizing-like interactions were found in this isotropic sample with large aspect ratio particles; also demagnetizing-like interactions were found for a thermally treated coprecipitated sample and a ceramic sample. [ABSTRACT FROM AUTHOR]

The magnetic properties and magnetic entropy changes of DyCo 2 B x ( x =0, 0.05, 0.1, and 0.2) alloys were investigated. The Curie temperature ( T C ) increases with increasing B concentration. The frequency dependence of ac magnetic susceptibility of DyCo 2 caused by the narrow domain wall pinning effect is depressed by B doping, but the coercivity and the magnetic viscosity are prominently increased in the B doped alloys. The magnetic transition nature of DyCo 2 B x changes from the first-order to the second-order with increasing x , which leads to the decrease of the maximum magnetic entropy change. However, the relative cooling power (RCP) of DyCo 2 and the B doped alloys remains nearly constant. [ABSTRACT FROM AUTHOR]

In this paper we present a comparative analysis of the magnetic interactions and reversal mechanisms of two different systems: NdFeB-type alloys with grain sizes in the single domain range and Fe-SiO2 nanocomposites with Fe concentrations above and below the percolation threshold. We evidence that the use of the coercivity as the main parameter to analyse them might be misleading due to the convolution of both reversible and irreversible magnetization variations. We show that the switching field and thermally assisted demagnetization allow a better understanding of these mechanisms since they involve just irreversible magnetization changes. Specifically, the experimental analysis of the coercivity adquisition process for the NdFeB-type system suggests that the magnetization reversal is nucleated at the spin misalignments present due to intergranular exchange interactions. On the other hand, the study of the magnetic viscosity and of the isothermal remanent magnetization (IRM) and direct field demagnetization (DCD) remanence curves indicates that the dipolar interactions are responsible for the propagation of the switching started at individual particles.En este artículo presentamos un análisis comparativo de la influencia de la microestructura a través de las interacciones magnéticas en los mecanismos de inversión de la magnetización en dos sistemas diferentes: aleaciones tipo NdFeB con tamaños de grano en el rango de monodominio y nanocompuestos de Fe-SiO2 con concentraciones de Fe tanto por encima como por debajo del umbral de percolación. Ponemos de manifiesto que el uso del campo coercitivo como parámetro de análisis puede llevar a equívocos debido a la coexistencia de variaciones reversibles e irreversibles de la magnetización. También mostramos que el campo de conmutación y la desimanación térmicamente asistida permiten una mejor comprensión de dichos mecanismos ya que reflejan exclusivamente cambios irreversibles de imanación. Concretamente, el análisis experimental del proceso de adquisición de coercitividad de los sistemas tipo NdFeB sugiere que la inversión de la magnetización se nuclea en los desalineamientos de los espines debidos a las interacciones de canje intergranular en las fronteras de grano. Por otra parte, el estudio de la viscosidad magnética y de las curvas de remanencia isoterma (IRM) y de remanencia de desimación DC (DCD) de los nanocompuestos de Fe-SiO2 indica que las interacciones dipolares son responsables en este sistema de la propagación de la conmutación, que se genera en partículas individualmente consideradas.

The exponential model of ferromagnetic susceptibility for steel has been extended to include ferromagnetic viscosity by comparing measured eddy current free susceptibility with the static exponential model. Viscous susceptibility and viscous field advance are derived from the definition of ferromagnetic viscosity. Measurements were performed on both a pipe in an isothermal yoke and a disk in a vibrating sample magnetometer. Yoke design is described and disk corrections for magnetized volume fraction and field demagnetization were computed using a quasistatic magnetization volume integral equation. Accuracy of this model suggests that the four parameters of the static model plus two parameters of the Gaussian model plus one eddy current delay parameter form a complete description of ferromagnetic hysteresis. • Designed and fabricated high field yoke to apply stress to isothermal pipe sample. •Verified computed volume and demagnetization corrections to VSM M(H) data. •Conceived of viscous Gaussian gain factor to precisely fit hysteresis and susceptibility data. •Achieved complete four process seven parameter ferromagnetic hysteresis model. [ABSTRACT FROM AUTHOR]

Abstract: Magnetic viscosity of rocks associated with magnetic relaxation of ultrafine ferrimagnetic mineral grains (superparamagnetism) is employed in magnetic grain size measurements. Magnetic viscosity is most often estimated from dual frequency measurements of magnetic susceptibility. The measured susceptibility values bear uncertainty that comprises two components: an instrument error and a drift. The instrument error refers to the accuracy of the measurement system and shows how precise the data are in ideal operation conditions. This error affects especially the low susceptibilities of weak samples, which thus should be measured on a high sensitivity range. Drift is due to external factors, such as changes in the temperature of sensors and/or samples, as well as in the orientation of the samples relative to the sensor, vibration, electromagnetic noise, etc. Drift, more critical for measurements on strong samples, is manageable by the operator. To reduce drift, every effort should be made to maintain suitable ‘quiet’ operation conditions. [Copyright &y& Elsevier]

The switching mechanism in two different types of hard-soft stacked, exchange-coupled composite perpendicular recording media was investigated through studies on magnetic viscosity, hysteresis reptation and reversibility. For the first set of samples, the anisotropy of the soft layer was much smaller and its intergranular exchange much stronger than that of the hard layer. For this set, the viscosity and reptation coefficients correlated with the switchability, as did peak recoil susceptibility. The athermal reversibility, which was obtained from the reptation measurements and is a measure of the reversible moment after subtracting thermal agitation, also correlated with the switchability. This media set exhibited a switching mechanism consistent with the exchange-spring effect in all aspects. For the second set of samples, where the anisotropy of the soft layer was only slightly smaller and its intergranular exchange slightly stronger than that of the hard layer, the media still exhibited improved switchability. However, no clear evidence for the exchange-spring effect could be found either in the viscosity or reptation curves, in the peak recoil susceptibility, or in the athermal reversibility. Thus the observations were consistent with the exchange-spring effect for the first set and not so for the second set. [ABSTRACT FROM AUTHOR]

Abstract: The bulk amorphous Nd45Pr15Fe30−x Co x Al10 (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 (χ irr) 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 H f increased from 9.9mT to 11.5mT, and the activation volume V a increased from 2.9×10–18 cm3 to 3.6×10–18 cm3, which leads to an increase of the activation diameter D a from 17.7nm to 19.0nm. The value of D a 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. [Copyright &y& Elsevier]

Abstract: The quasilogarithmic magnetic viscosity of the perpendicularly anisotropic Nd–Fe–B films is determined by measuring the time dependent magnetization in coercive fields at 300K–4.2K. The distribution of energy barrier heights in the films is believed to be the origin of this stretched exponential magnetic relaxation. Another feature exhibited in the anisotropic Nd–Fe–B films is the nonmonotonic temperature dependence of the magnetic viscosity coefficients, which are extracted by the decay slopes of the linear quasilogarithmic magnetic aftereffect curves. [Copyright &y& Elsevier]

Abstract: This work is an investigation of the experimental method used for measuring the magnetic viscosity in a hard ferromagnetic material, i.e. the recording of the magnetization under constant applied field and temperature, after the material has been magnetically saturated. It investigates how the experimental results are affected by the initial conditions of the method (saturation field, field change rate and field oscillation prior to its stabilization), and by minor variations of field and temperature during the recording. Based on the arising conclusions and the use of a more complex fitting function of measurements, the accuracy and repeatability of experimental results is improved. [Copyright &y& Elsevier]

Intercrystallite magnetic interaction in nanostructured films for magnetic recording and magnetic microelectronics and also its correlation with magnetic properties and performance characteristics of materials is analyzed on the basis of investigation of δ M curves, data of Mössbauer spectroscopy, the anomalous Hall effect, etc. [ABSTRACT FROM AUTHOR]

Abstract: This article presents an anomalous magnetic viscosity in exchange-spring magnet. A similar effect has been observed in non-interacting or weakly interacting systems but not in a strong interacting magnetic systems. We reported a new procedure to measure magnetic relaxation under various magnetic fields. Changing the applied magnetic field by different field protocols during the reversal process, we found that a memory effect of the magnetization appeared if the field change is large enough. The mechanism of the phenomenon can be explained in the model of conventional magnetic reversal in strong ferromagnetic systems with an energy barrier distribution. The study of such magnetic relaxations can provide some information related to the energy barrier distribution function. [Copyright &y& Elsevier]

We report the temperature dependent coercivity behavior and the improvement of room temperature soft magnetic properties in interacting amorphous Fe-Mn-Zr-B powder nanoparticles prepared by mechanical alloying of elemental powders. With increasing Mn concentration from 5 to 20 at.% in Fe-Zr-B alloys, the coercivity (HC) reduces drastically from 170 to 25 Oe. Temperature dependent HC behavior shows exponential variation of HC with temperature. Interparticle interactions dominate the low temperature behavior and surface effect on the nanoparticles is more pronounced at low temperatures. Magnetic relaxation behavior shows slow relaxation in the interacting amorphous nanoparticles and the relaxation process is observed to be thermally activated in the present studies. [ABSTRACT FROM AUTHOR]

Abstract: We have modeled central-loop and coincident-loop transient responses of a magnetically viscous layer sandwiched between two nonmagnetic ones. The coincident-loop transients show exponential voltage decrease (at a fixed delay time), at any thickness h 2 of the magnetic layer, with an increasing depth to the latter (h 1) or the loop height if the layer is exposed on the ground surface. The patterns of central-loop transients are different from those of the coincident-loop ones and from one another for thin and thick magnetic layers. Namely, the voltage first rises to its maximum and then falls as the depth to the magnetic layer (h 1) increases, if it is thin: the thinner the layer, the more prominent the peak. If the layer is thick, the voltage decreases monotonically with its depth (or with loop height above the ground). Voltage grows, first rapidly and then progressively more slowly, at ever greater thicknesses of the magnetic layer in both loop configurations. At large h 2, the effect from the magnetic layer becomes similar to that from a magnetically viscous halfspace. These features of the transient responses have to be taken into account in planning and conducting TEM surveys, as well as in a geological interpretation of the TEM data affected by natural and/or man-caused magnetically viscous ground. In the general case, the turn-off of the transmitter current induces eddy current in the ground beneath the loop, which decays at a rate proportional to the ground resistivity. The eddy current decay and magnetic relaxation processes being independent at conductivities (resistivities) common to the real subsurface, the effect of the former can be allowed for using the superposition principle. This principle implies that the total response of a magnetically viscous conductor is a sum of the magnetic relaxation and eddy current components. [Copyright &y& Elsevier]

Abstract: We discuss the results of a field experiment in the Malaya Botuobiya area (West Yakutia) at a site where earlier surveys revealed slowly decaying transient responses. That time-dependent voltage decay indicated magnetic viscosity effects associated with magnetic relaxation of superparamagnetic grains in rocks. In this study, we have applied a high-resolution array TEM survey to contour the anomaly and parametric soundings with systems of different configurations to explore the vertical pattern of magnetic viscosity. The parametric data have been inverted, by means of manual and automated fitting, with a reference model of a layered magnetically viscous earth, using, respectively, analytical formulas and simulation based on a forward solution by separation of variables. According to both automated and manual inversion, the section at the center of the anomalous site fits a three-layer earth model with an intermediate magnetically viscous layer between two nonmagnetic layers. This model is consistent with a priori evidence of local geology and may provide more details of the latter. The inversion results have been further used to estimate the volumetric percentage of superparamagnetic grains in the magnetically viscous layer, assuming magnetite to be the main ferrimagnetic phase. [ABSTRACT FROM AUTHOR]

Abstract: We have developed a simple numerical model for simulating domains as well as remanence and viscosity curves in the slow dynamics regime, for thin films characterized by perpendicular magnetization and irregular domain configurations due to strong disorder. The physical system is represented as constituted of identical switching units, described by proper switching field distributions and energy barrier laws for pinning and nucleation processes. The model also includes an effective field which accounts for magnetic forces proportional to magnetization, on average. Simulations of DCD curves show that when the reversal of magnetization is governed by pinning, the coercive field depends on the physical size of the film area on which the external field is applied. In the case of viscosity phenomena described by a linear energy barrier law associated with a single predominant reversal process (pinning or nucleation), universal viscosity curves can be generated by properly transforming the DCD curve of the system. We also demonstrate that a reduction of the maximum viscosity coefficient can coexist with a reduction of the energy barrier heights. [Copyright &y& Elsevier]