Magnetization reversal in systems of interacting magnetically hard particles

Abstract In this contribution, a magnetoactive elastomer (MAE) of mixed content, i.e., a polymer matrix filled with a mixture of magnetically soft and magnetically hard spherical particles, is considered. The object we focus on is an elementary unit of this composite, for which we take a set consisting of a permanent spherical micromagnet surrounded by an elastomer layer filled with magnetically soft microparticles. We present a comparative treatment of this unit from two essentially different viewpoints. The first one is a coarse-grained molecular dynamics simulation model, which presents the composite as a bead-spring assembly and is able to deliver information of all the microstructural changes of the assembly. The second approach is entirely based on the continuum magnetomechanical description of the system, whose direct yield is the macroscopic field-induced response of the MAE to external field, as this model ignores all the microstructural details of the magnetization process. We find that, differing in certain details, both frameworks are coherent in predicting that a unit comprising magnetically soft and hard particles may display a nontrivial reentrant (prolate/oblate/prolate) axial deformation under variation of the applied field strength. The flexibility of the proposed combination of the two complementary frameworks enables us to look deeper into the manifestation of the magnetic response: with respect to the magnetically soft particles, we compare the linear regime of magnetization to that with saturation, which we describe by the Fröhlich–Kennelly approximation; with respect to the polymer matrix, we analyze the dependence of the reentrant deformation on its rigidity.

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Modeling the magnetostriction effect in elastomers with magnetically soft and hard particles

Soft Matter ◽

10.1039/c9sm00827f ◽

2019 ◽

Vol 15 (36) ◽

pp. 7145-7158 ◽

Cited By ~ 8

Author(s):

Pedro A. Sánchez ◽

Oleg V. Stolbov ◽

Sofia S. Kantorovich ◽

Yuriy L. Raikher

Keyword(s):

Polymer Matrix ◽

Hard Particles ◽

Magnetically Hard ◽

Spherical Microparticles

We analyze theoretically the field-induced microstructural deformations in a hybrid elastomer that consists of a polymer matrix filled with a mixture of magnetically soft and magnetically hard spherical microparticles.

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Hybrid magnetic elastomers prepared on the basis of a SIEL-grade resin and their magnetic and rheological properties

Physical Sciences Reviews ◽

10.1515/psr-2020-0008 ◽

2020 ◽

Vol 0 (0) ◽

Cited By ~ 1

Author(s):

Gennady V. Stepanov ◽

Dmitry Yu. Borin ◽

Anton V. Bakhtiiarov ◽

Pavel A. Storozhenko

Keyword(s):

Magnetic Field ◽

Rheological Properties ◽

Magnetic Moments ◽

Mechanical Analysis ◽

Hard Particles ◽

Steady Growth ◽

A Value ◽

Magnetically Hard ◽

The Relationship ◽

Magnetic Elastomers

Abstract Hybrid magnetic elastomers (HMEs) belong to a novel type of magnetocontrollable elastic materials capable of demonstrating extensive variations of their parameters under the influence of magnetic fields. Like all cognate materials, HMEs are based on deformable polymer filled with a mixed or modified powder. The complex of properties possessed by the composite is a reflection of interactions occurring between the polymer matrix and the particles also participating in interactions among themselves. For example, introduction of magnetically hard components into the formula results in the origination of a number of significantly different behavioral features entirely unknown to magnetorheological composites of the classic type. Optical observation of samples based on magnetically hard filler gave the opportunity to establish that initial magnetization imparts magnetic moments to initially unmagnetized grains, as a result of which chain-like structures continue to be a feature of the material even after external field removal. In addition, applying a reverse field causes them to turn into the polymer as they rearrange into new ring-like structures. Exploration of the relationship between the rheological properties and magnetic field conducted on a rheometer using vibrational mechanical analysis showed an increase of the relative elastic modulus by more than two orders of magnitude or by 3.8 MPa, whereas the loss factor exhibited steady growth with the field up to a value of 0.7 being significantly higher than that demonstrated by elastomers with no magnetically hard particles. At the same time, measuring the electroconductivity of elastomers filled with a nickel-electroplated carbonyl iron powder made it possible to observe that such composites demonstrated an increase of variation of the resistivity of the composite influenced by magnetic field in comparison to elastomers containing untreated iron particles. The studies conducted indicate that this material exhibits both magnetorheological and magnetoresistive effect and does indeed have the potential for use in various types of devices.

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Determination of eddy current losses and hysteresis losses in magnetic circuits of electrical machines

Izmeritel`naya Tekhnika ◽

10.32446/0368-1025it.2020-11-54-58 ◽

2020 ◽

pp. 54-58

Author(s):

S. M. Plotnikov

Keyword(s):

Eddy Current ◽

Magnetization Reversal ◽

Eddy Currents ◽

Technical Problem ◽

Electrical Machines ◽

Eddy Current Losses ◽

Hysteresis Losses ◽

Magnetic Circuits ◽

Core Losses ◽

Reversal Frequency

The division of the total core losses in the electrical steel of the magnetic circuit into two components – losses dueto hysteresis and eddy currents – is a serious technical problem, the solution of which will effectively design and construct electrical machines with magnetic circuits having low magnetic losses. In this regard, an important parameter is the exponent α, with which the frequency of magnetization reversal is included in the total losses in steel. Theoretically, this indicator can take values from 1 to 2. Most authors take α equal to 1.3, which corresponds to the special case when the eddy current losses are three times higher than the hysteresis losses. In fact, for modern electrical steels, the opposite is true. To refine the index α, an attempt was made to separate the total core losses on the basis that the hysteresis component is proportional to the first degree of the magnetization reversal frequency, and the eddy current component is proportional to the second degree. In the article, the calculation formulas of these components are obtained, containing the values of the total losses measured in idling experiments at two different frequencies, and the ratio of these frequencies. It is shown that the rational frequency ratio is within 1.2. Presented the graphs and expressions to determine the exponent α depending on the measured no-load losses and the frequency of magnetization reversal.

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Magnetic Aftereffect and Magnetization Reversal of Sr-Ferrite Fine Particles.

Journal of the Magnetics Society of Japan ◽

10.3379/jmsjmag.18.193 ◽

1994 ◽

Vol 18 (2) ◽

pp. 193-196 ◽

Cited By ~ 3

Author(s):

H. Nishio ◽

H. Taguchi ◽

F. Hirata ◽

T. Takeishi

Keyword(s):

Magnetization Reversal ◽

Fine Particles ◽

Magnetic Aftereffect

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COMPUTER SIMULATIONS OF MAGNETIZATION REVERSAL DYNAMICS

Journal of the Magnetics Society of Japan ◽

10.3379/jmsjmag.17.s1_255 ◽

1993 ◽

Vol 17 (S_1_MORIS_92) ◽

pp. S1_255-257 ◽

Cited By ~ 1

Author(s):

Roscoe C. Giles ◽

Masud Mansuripur

Keyword(s):

Computer Simulations ◽

Magnetization Reversal

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Magnetization dynamics of irradiation-fabricated perpendicularly magnetized dots inside a softer magnetic matrix

MRS Proceedings ◽

10.1557/proc-777-t6.4 ◽

2003 ◽

Vol 777 ◽

Cited By ~ 2

Author(s):

T. Devolder ◽

M. Belmeguenai ◽

C. Chappert ◽

H. Bernas ◽

Y. Suzuki

Keyword(s):

Domain Wall ◽

Magnetic Anisotropy ◽

Magnetization Reversal ◽

Ion Irradiation ◽

Magnetic Nanostructures ◽

Magnetic Storage ◽

Exchange Field ◽

Static Magnetization ◽

Specific Domain ◽

Helium Ion

AbstractGlobal Helium ion irradiation can tune the magnetic properties of thin films, notably their magneto-crystalline anisotropy. Helium ion irradiation through nanofabricated masks can been used to produce sub-micron planar magnetic nanostructures of various types. Among these, perpendicularly magnetized dots in a matrix of weaker magnetic anisotropy are of special interest because their quasi-static magnetization reversal is nucleation-free and proceeds by a very specific domain wall injection from the magnetically “soft” matrix, which acts as a domain wall reservoir for the “hard” dot. This guarantees a remarkably weak coercivity dispersion. This new type of irradiation-fabricated magnetic device can also be designed to achieve high magnetic switching speeds, typically below 100 ps at a moderate applied field cost. The speed is obtained through the use of a very high effective magnetic field, and high resulting precession frequencies. During magnetization reversal, the effective field incorporates a significant exchange field, storing energy in the form of a domain wall surrounding a high magnetic anisotropy nanostructure's region of interest. The exchange field accelerates the reversal and lowers the cost in reversal field. Promising applications to magnetic storage are anticipated.

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Exchange-Biasing in a Dinuclear Dysprosium(III) Single-Molecule Magnet with a Large Energy Barrier for Magnetization Reversal

10.26434/chemrxiv.10260494 ◽

2019 ◽

Author(s):

Tian Han ◽

Marcus J. Giansiracusa ◽

Zi-Han Li ◽

You-Song Ding ◽

Nicholas F. Chilton ◽

...

Keyword(s):

Single Molecule ◽

Magnetization Reversal ◽

Energy Barrier ◽

Magnetic Hysteresis ◽

Large Energy ◽

Magnetic Studies ◽

Bridging Ligands ◽

Single Molecule Magnet ◽

Exchange Biasing

A dichlorido-bridged dinuclear dysprosium(III) single-molecule magnet [Dy2L2(µ-Cl)2(THF)2] has been made using a diamine-bis(phenolate) ligand, H2L. Magnetic studies show an energy barrier for magnetization reversal (Ueff) around 1000 K. Exchange-biasing effect is clearly seen in magnetic hysteresis with steps up to 4 K. Ab initio calculations exclude the possibility of pure dipolar origin of this effect leading to the conclusion that super-exchange via the chloride bridging ligands is important.

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