Influence Of Magnetic Interactions Research Articles

Influence of magnetic interaction on four-peak GMI profile in FINEMET/Fe35Ni65 composite ribbons

The study of magnetic interactions is crucial in understanding magnetic materials, where both exchange coupling and dipole interactions significantly affect the magnetic properties of composite materials. Separating and utilizing these two types of interactions have consistently been a research focus. In this study, FINEMET/Fe35Ni65 composite ribbons with varying coating thicknesses were fabricated using magnetron sputtering. Notably, obvious four-peak giant magnetoimpedance profiles can be observed as the Fe35Ni65 film thickness varied from 10 to 50 nm. Additionally, the manifestation of the four-peak profile was attributed to the variation in the magnetic properties in the FINEMET ribbon induced by exchange coupling and dipole interaction. This analysis is crucial for advancing our understanding of the underlying physical mechanisms of magnetic interactions in composite ribbons.

Influence of magnetic interactions in iron oxide nanoparticle polymer composites on magnetism and induction heating

Induction heating of composite materials is of great interest in fields such as controlled polymer curing or degradation, self-healing or contactless joining. Ferrimagnetic iron oxide nanoparticle (IONPs) are suitable candidates for a powder additive to provide this inductive heating functionality, while being low-cost, abundant and a well-studied material class. Varying IONP size, morphology or doping facilitates fine-tuning of their heating properties. However, the interactions of such IONP additives in material composites are often neglected and can significantly alter the induction heating mechanism. In this work, we systematically vary the IONP interactions in polydimethylsiloxane composite materials by integrating 1.) dispersed IONPs 2.) supraparticles of IONPs (micrometer-assemblies), and 3.) oven-dried hard agglomerated IONPs. Additionally, these three levels of interaction are investigated for three different IONPs types (dodecahedrally and octahedrally shaped, as well as cobalt-doped). In general, dispersed IONPs reveal a broader hysteresis and therefore a faster heating curve. We highlight that not only IONP characteristics (size, morphology, doping), but also excitation field strength and foremost IONP interactions in the composite materials are parameters that are interdependent regarding induction heating and need to be considered as such for optimization in an application-oriented scenario.

Do Electrostatics Control the Diffusive Dynamics of Solitary Water? NMR and MD Studies of Water Translation and Rotation in Dipolar and Ionic Solvents.

NMR-based measurements of the diffusion coefficients and rotation times of solitary water and benzene at 300 K are reported in a diverse collection of 13 conventional organic solvents and 10 imidazolium ionic liquids. Proton chemical shifts of water are found to be correlated to water OH-stretching frequencies, confirming the importance of electrostatic interactions in these shifts. However, the influence of magnetic interactions in aromatic solvents renders chemical shifts a less reliable indicator of electrostatics. Diffusion coefficients (DB) and rotational correlation times (τB) of benzene in the solvents examined are accurately described as functions of viscosity (η) by DB ∝ η-0.81 and τB ∝ η0.64. Literature values of DB and τB in alkane and normal alcohols, which were not included among the solvents studied here, are systematically faster than predicted by these correlations, indicating that factors beyond solvent viscosity play a role in determining the friction on benzene. In contrast to benzene, water diffusion and rotation are poorly described in terms of viscosity alone, even in the dipolar and ionic solvents measured here. The present data and the substantial literature data already available on dilute water diffusion show a systematic dependence of DW on solvent polarity among isoviscous solvents. The aspect of solvent polarity most relevant to water dynamics is the ability of a solvent to accept hydrogen bonds from water, as conveniently quantified by the frequency of water's OH stretching band, ΔνOH. The friction on translation, ζtr = kBT/DW, and rotation, ζrot = kBTτW, are both well correlated by functions of the form ζ(η, ΔνOH) = a1ηa2 exp (a3ΔνOH), where the ai are adjustable parameters. Molecular dynamics simulations reveal a strong coupling between electrostatic and nonelectrostatic water-solvent interactions, which makes it impossible to dissect the friction on water into additive dielectric and hydrodynamic components. Simulations also provide a tentative explanation for the unusual form of the correlating function ζ(η, ΔνOH), at least in the case of ζrot.

Influence of magnetic interaction on configurational-entropy-suppressed β -relaxations in FeNi-based metallic glasses

In this article, we studied the effect of magnetic interaction on β-relaxations of FexNi72−xSi4.8B19.2Nb4 (x = 0, 10, 30, 50, 72) metallic glasses (MGs). It is found that, with the substitution of Fe by Ni, the β-relaxation changes from a shoulder to an excess wing, suggesting an entropic effect on the suppression of β-relaxation. A peak caused by ferromagnetic transformation appears in the loss modulus curve of Fe30Ni42Si4.8B19.2Nb4 MG with suppressed β-relaxation, which is sensitive to stress and strain. In addition, the β-relaxation can be further varied by annealing under a transverse or longitudinal magnetic field. The results suggest that the entropy-suppressed β-relaxation in MGs can be affected by magnetic interaction that could help to improve their mechanical properties.

Theoretical and numerical analysis of regular one-side oscillations in a single pendulum system driven by a magnetic field

This paper presents a theoretical and numerical analysis of one-side oscillation in a single magnetic pendulum. The system is composed of a physical pendulum with a neodymium magnet fixed to the end of the rod. The pendulum is driven by a pulsating, repulsive magnetic field generated by an electric coil placed underneath. The pendulum pivot is damped by an elastic element. The excitation current signal has a pulsating rectangular waveform with a controlled frequency and duty cycle. In general, magnetic interaction weakens with increasing distance between the magnet and the coil, making excitation in this system not only time-dependent but also position-dependent. The specific type of solution, referred to as “one-side oscillation” is analysed in terms of a frequency and a duty cycle of the current signal. By one-side oscillations, we mean oscillations of the pendulum characterized by the same sign of angular displacement, without passing through the lowest and the highest vertical equilibrium positions. The analysis is based mainly on the assumption that outside some “active zone” the influence of magnetic interaction on the pendulum dynamics is negligible, and the system can be discretized into two states: with and without magnetic force. The results were confirmed by experimental data showing the different periodicity of one-side oscillations. Limitations of the proposed analysis were found in the case of some variants of the analysed solution type. An overview of the system dynamics is presented in the form of bifurcation diagrams obtained numerically and verified by experimental estimates, which show the existence of chaotic behaviour and multiperiodicity for various values of the frequency of the current signal.

Influence of Magnetic Interactions and Single-Ion Anisotropy on Magnetic Relaxation within a Family of Tetranuclear Dysprosium Complexes.

Six tetranuclear DyIII complexes [Dy4(L)2(CH3OH)3(NO3)3]·3NO3·2H2O (1a), [Dy4(L)2(CH3OH)2(SCN)4(OCH3)2]·2CH3OH·2H2O (1b), {[Dy4(L)2(CH3OH)(SCN)6(CH3CN)]·3CH3OH·4CH3CN}2 (2a), [Dy4(L)2(CH3OH)2(SCN)6]·6CH3OH·2H2O (2b), [Dy4(L)2(CH3OH)2(SCN)4(OCH3)2]·5CH3OH·2H2O (3a), and [Dy4(L)2(CH3OH)(SCN)5(H2O)2]·SCN·4CH3OH·2H2O (3b) were structurally and magnetically characterized. The Dy1/Dy2 centers in these complexes are eight-coordinate and submitted to pseudo- D4d symmetry environments. It is noteworthy that the modulation of coordination terminal around Dy1/Dy2 centers induces distinct magnetic relaxation processes, switching from single relaxation (1b) to two-step relaxation (2b). All complexes show significant zero-field single-molecule magnet (SMM) properties with the exception of 3b, which only features the slow magnetic relaxation behavior under a zero dc field. Ab initio calculations substantiate that the excellent SMM property of complex 1b should mainly profit from strong ferromagnetic interactions between the individual DyIII ions, while different single-ion magnetism results in better SMM property of complex 3a than that of 3b.

Analysis and experiment of magneto-mechanically coupled harvesters

Abstract Current trend in energy harvesting research is to increase the operating bandwidth of energy harvesters. Multiple harvesters, nonlinear harvesters and hybrid harvesters are suggested to address the issue. In this paper, a system consisting of two electromagnetic harvesters with magnetic and mechanical couplings subjected to harmonic support excitations is proposed. Two pendulums with close resonating frequencies are used to generate power over a broad range of frequencies. The pendulums behave nonlinearly under the influence of magnetic interaction. This nonlinear motion harvests power at broader bandwidth. A mathematical model of the proposed harvester is established. Experiments are performed to validate the theoretical results. It has been observed that the nonlinear responses due to both magnet and mechanical couplings improve individual harvester performance. This is advantageous over harvesters that have magnetically coupling only. Additionally, the dynamics of harvesting system is numerically studied where large amplitude chaotic motion, quasi-periodic oscillations and periodic motions are observed and reported.

The Influence of Magnetic Interaction on Magnetic Structure of Domain Walls in Metallic Ferromagnetic Nanofilms

Using transmission electron microscopy, the structure of domain walls is investigated in Fe0.2–Ni0.8 alloy and nickel nanofilms. It is shown that it is controlled not only by the film thickness but also by the angle between the magnetization vector I s and the easy magnetization axis. Applying an external magnetic field along the hard magnetization axis, the field values at which the domain wall structure varies are considered. As the domain wall density becomes higher, the field interval, where magnetization variations occur, is found to increase sharply.

Methods to reduce cogging torque of permanent magnet synchronous generator used in wind power plants

This paper presents five latest methods and explains the last- new one with intention to reduce the cogging torque of permanent magnet synchronous generators (PMSG). The PMSGs are widely used in wind power plants (WPP) as one of the renewable power generation. One of the international goals is to expand the use of renewable energy sources. The main disadvantage of PMSG is the influence of magnetic interaction between the magnets and the teeth on the operation of PMSG, thus many scientists have been researching the possibilities to reduce the cogging torque. The magnetic field modelling software is used to obtain the values of PMSG cogging torque. The calculations in this software are based on finite element analysis. A methodology is created to obtain the 3D results from the 2D modelled magnetic field. The achieved results allowed to submit a patent. The new proposed method is researched allowing to receive the first results of PMSG optimal design, thus expanding the lower boundary of operating wind speed for WPP. DOI: http://dx.doi.org/10.5755/j01.eie.23.1.12714

Particle Interactions in Liquid Magnetic Colloids by Zero Field Cooled Measurements: Effects on Heating Efficiency

The influence of magnetic interactions in assemblies formed by either aggregated or disaggregated uniform γ-Fe2O3 particles are investigated as a function of particle size, concentration, and applied field. Hyperthermia and magnetization measurements are performed in the liquid phase of colloids consisting of 8 and 13 nm uniform γ-Fe2O3 particles dispersed in water and hexane. Although hexane allows obtaining the disagglomerated particle system, aggregation is observed in the case of water colloids. The zero field cooled (ZFC) curves show a discontinuity in the magnetization values associated with the melting points of water and hexane. Additionally, for 13 nm γ-Fe2O3 dispersed in hexane, a second magnetization jump is observed that depends on particle concentration and shifts toward lower temperature by increasing applied field. This second jump is related to the strength of the magnetic interactions as it is only present in disagglomerated particle systems with the largest size, i.e., is not observed fo...

Influences of Magnetic Interactions Between the Spin-Torque Oscillator, SPT Writer, and Recording Medium on Recording Performance in MAMR

Microwave-magnetic recording (MAMR) has the potential to overcome the trilemma in magnetic recording technology. The capability of MAMR has mainly been investigated using numerical calculations. Thus, it is important to improve the reliability of such simulations with the aim of using them to realize feasible MAMR. Conventional simulations, in particular, seem to neglect the magnetic interactions between the spin-torque oscillator (STO), Single-Pole Type (SPT) writer, and recording medium. We have developed a MAMR simulator that takes into account the complete magnetic interactions. In this paper, we compare three models: a conventional model; a one-way interaction model that considers only the interactions from the STO to the SPT writer; and our complete interaction model. The recording performances found are remarkably different, depending on the model used, suggesting that it is necessary to use a simulator that takes into account the full range of interactions.

The influence of magnetic interactions and shape anisotropy on the alignment and assembly of BaFe12O19 and Er2O3 nanoplates

Magnetically anisotropic material with useful properties can be obtained when the barium ferrite (BaFe12O19) plates are aligned in a single plane. We studied the influence of the magnetic forces and the shape anisotropy on the alignment of barium ferrite nanoparticles. Nanoplates with diameters of 10–350 nm and diameter-to-thickness ratios of 3–30 were synthesized hydrothermally and stabilized in 1-butanol with dodecylbenzene sulphonic acid. The nanoplates were then deposited from the suspension on gold-coated substrates and dried with or without an applied magnetic field. In both cases the nanoplates aligned preferentially in the plane of the substrate, as evidenced by the scanning electron microscopy observations. To compare the influence of the magnetic field and the magnetic dipole–dipole interactions with that of the nanoparticle shape anisotropy, the alignment of paramagnetic erbium oxide (Er2O3) nanoplates was also studied. A lower degree of alignment was obtained with the erbium oxide than with the barium ferrite nanoplates. Barium ferrite films with a minimum orientation of 90% were prepared from the deposits after sintering at 1150 °C for 5 h. A comparable alignment of the erbium oxide films was induced hydrodynamically during the electrophoretic deposition.

Thermodynamic Stability of Fe-Cr Binary System: The Crucial Role of Magnetic Contribution as Elucidated by Calorimetric Measurements

The influence of magnetic interactions on high temperature thermodynamic stability of Fe-Cr binary system has been analysed in the light of accurate isothermal calorimetry measurements (400-1473 K) on Fe-20wt.%Cr alloy. The onset of two successive principal transformations namely, (i) α(Fe-rich bcc)+α(Cr rich bcc)α(HT bcc) at 702±10 K; and (ii) αferroαpara at 925 ±10 K, with their associated enthalpy effects (ΔoHmag = 2 kJ mol -1; Cpmag = 20 J mol-1 K-1) have been clearly delineated by the measured enthalpy variation with temperature. A precise quantification of magnetic contribution to high temperature thermodynamic stability has been attempted using physically based modelling approach.

Increase of magnetic hyperthermia efficiency due to dipolar interactions in low-anisotropy magnetic nanoparticles: Theoretical and experimental results

When magnetic nanoparticles (MNPs) are single-domain and magnetically independent, their magnetic properties and the conditions to optimize their efficiency in magnetic hyperthermia applications are now well-understood. However, the influence of magnetic interactions on magnetic hyperthermia properties is still unclear. Here, we report hyperthermia and high-frequency hysteresis loop measurements on a model system consisting of MNPs with the same size but a varying anisotropy, which is an interesting way to tune the relative strength of magnetic interactions. A clear correlation between the MNP anisotropy and the squareness of their hysteresis loop in colloidal solution is observed : the larger the anisotropy, the smaller the squareness. Since low anisotropy MNPs display a squareness higher than the one of magnetically independent nanoparticles, magnetic interactions enhance their heating power in this case. Hysteresis loop calculations of independent and coupled MNPs are compared to experimental results. It is shown that the observed features are a natural consequence of the formation of chains and columns of MNPs during hyperthermia experiments: in these structures, when the MNP magnetocristalline anisotropy is small enough to be dominated by magnetic interactions, the hysteresis loop shape tends to be rectangular, which enhance their efficiency. On the contrary, when MNPs do not form chains and columns, magnetic interactions reduces the hysteresis loop squareness and the efficiency of MNPs compared to independent ones. The present work should improve the understanding and interpretation of magnetic hyperthermia experiments.

Influence of magnetic interactions between phases on the magnetocaloric effect of composites

Magnetocaloric materials with coexisting magnetic phases appear either due to the phase coexistence in first order phase transitions, or due to the development of composites, which are known to enhance the refrigerant capacity and produce table-like magnetocaloric effect. However, interactions between phases are rarely considered. We have modeled the influence of interactions on the magnetocaloric effect of a biphasic composite by implementing a mean field model. Interactions shift the peak magnetic entropy change to higher temperatures than those of the pure phases and enhance the table-like character of the curves. Although there is no qualitative change of the magnetocaloric response of the composites due to interactions, the optimal fraction of phases which produces the largest enhancement of the refrigerant capacity is shifted to compositions richer in the low Curie temperature phase. This shift can be used to estimate the magnitude of the interactions in composites measured experimentally.

Microstructure, magnetic and transport properties of magnetoresistive Cu80Fe x Ni20−x (x = 5, 10 and 15 at.%) ribbons

Microstructure, magnetic and transport properties of magnetoresistive Cu80FexNi20−x (x = 5, 10 and 15 at.%) melt-spun ribbons were studied for the as-spun and annealed for 2 h at 400 to 600 °C samples. The microstructure was characterised by means of X-ray diffraction, transmission electron microscopy, energy filtered transmission electron microscopy and Mossbauer spectrometry (MS). Magnetic and transport measurements such as magnetization, zero field cooled/field cooled and giant magnetoresistance (GMR) measurements at 5 and 300 K were performed. The aim of this work is to study the influence of the microstructure of as-spun and annealed ribbons on magnetic and transport properties at 5 and 300 K. We have precisely determined the nature of precipitation of nanoparticles, the relative proportion and the magnetic properties of each phase in such a system using MS at both temperatures. We report the conclusive observation of the magnetic behaviour of each phase which was correlated to the structural data to explain the GMR properties that are observed. The influence of magnetic interactions between nanoparticles on magnetic and magnetoresistive properties of these ribbons was determined. We have clearly shown the existence and the nature of the magnetic interactions that reduce the GMR.

Influence of magnetic interactions on the anisotropy of magnetic susceptibility: the case of single domain particles packed in globule aggregates

The influence of magnetic interactions on the anisotropy of magnetic susceptibility (AMS) have been largely studied by several theoretical models or experiments. Numerical models have shown that when magnetostatic interactions occur, the distributions of particles over the volume rather than their individual orientations control the AMS. We have shown recently from a comprehensive rock magnetic study and from a theoretical 2-dimensional (2-D) model that single domain particles closely packed in globule aggregates could produce strong local random interaction magnetic fields which could influence the magnetic susceptibility and decrease the degree of anisotropy. In this paper, we first present in detail this 2-D theoretical model and then we extend it to the 3-D case. The possible distribution function of the magnetostatic interaction fields comprises two extreme states: it is either isotropic or ordered. The former case corresponds to the thermal-demagnetized state while the second case corresponds to the alternating field (AF) demagnetized state. We show that when easy axes of magnetization are not uniformly distributed, the degree of anisotropy decreases as the interaction field increases in both AF- and thermal-demagnetized states in 2-D and 3-D geometry. Thus we conclude that random magnetic fields generated by a random arrangement of magnetic particles over the sample volume decrease the degree of anisotropy of AMS and may alter the magnetic fabric.

A detailed paleomagnetic record between 2.1 and 2.75 Ma at IODP Site U1314 in the North Atlantic: Geomagnetic excursions and the Gauss‐Matuyama transition

This study investigated the detailed geomagnetic field variation between 2.1 and 2.75 Ma from a sediment core (IODP Site U1314) with high sedimentation rate (≥10 cm/kyr) and good age control. Characteristic remanent magnetization directions were well resolved by stepwise alternating field demagnetization. As a proxy of relative paleointensity, natural remanent magnetization (NRM) normalized by anhysteretic remanent magnetization (ARM) was used after testing that the influence of magnetic interaction in ARM is negligible. As a result, the following features of the geomagnetic field in the studied period have been revealed. During the transition of the Gauss‐Matuyama (G‐M) reversal and the Réunion Subchron, the paleointensity decreased to the value lower than 20% of the average intensity in the whole studied interval. In addition to these lows, eight paleointensity lows were found associated with large directional changes that satisfy the definition of a geomagnetic excursion. Four of these have ages close to ages reported for geomagnetic excursions in prior studies, whereas the other four excursions have not previously been observed. In our results, we confirm that the G‐M transition occurred in marine isotope stage 103 even if we consider the shift in depth due to the lock‐in process of magnetic particles. The temporal variation in paleointensity showed asymmetric behavior associated with the G‐M transition, with a gradual decrease prior to the transition and a rapid recovery after the transition.

磁性扁平粒子からなる高濃度サスペンションの相転移と内部構造発現現象に関する擬2次元モンテカルロ・シミュレーション(流体工学,流体機械)

We have investigated phase transitions and internal aggregate structures of a highly dense suspension composed of magnetic plate-like particles with a magnetic moment normal to the particle axis, by means of the Monte Carlo method. In the present study, we have considered a quasi-2D system in order to clarify the influences of the volumetric fraction of particles and magnetic field strength on particle aggregations and phase transitions. Internal structures of particle aggregates have been discussed quantitatively in terms of pair correlation and orientational pair correlation functions. The main results obtained here are summarised as follows. When the influence of magnetic interactions between particles is of the same order of the magnetic field strength, the particles form column-like clusters, and the internal structure of a dispersion shows solid-like structures. As the magnetic field strength becomes strong, the internal structure of a dispersion is transformed from solid-like structures into isotropic ones. However, as the volumetric fraction increases, the particles form brick wall-like structures under circumstances of a strong applied magnetic field, and the internal structure of a dispersion exhibits solid-like ones.

Influence of magnetic interactions on magnetic and magnetoresistive properties of Cu80Fe10Ni10 ribbons

Magnetic and magnetotransport properties measurements of Cu80Fe10Ni10 (at. %) melt spun and annealed ribbons were combined to study the magnetic interactions present in this system. Those ribbons are composed of magnetic FeNi rich precipitates embedded in a nonmagnetic Cu rich matrix. When the precipitates are small enough, they have a superparamagnetic behavior. Upon annealing the precipitates get larger and progressively turn ferromagnetic. The relatively high magnetoresistive properties are attributed to the presence of those superparamagnetic precipitates. Using Mössbauer spectrometry, Zero Field Cooled/Field Cooled and magnetization curves, the presence of interactions among the precipitates was evidenced, which degrades the magnetoresistance properties. Using Allia model, the magnetic coherence length Rm between the precipitates was calculated and compared with the mean free path of the electrons λ, with the precipitates size and the mean distance between them. Three different regimes were observed. At high fields, where Rm<λ, meaning that the precipitates are not interacting, at smaller fields, where Rm>λ and the precipitates are in the so called “interacting superparamagnetic regime,” and at low fields, and at 5 K, Rm>10λ, the magnetic interactions among the precipitates are strong and give rise to a hysteresis on the magnetization curves.