Exchange-Coupled Nanocomposite Permanent Magnets

Liu, J.P.

doi:10.1007/978-0-387-85600-1_11

Cited by 32 publications

(29 citation statements)

References 82 publications

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“…Traditionally the search for new permanent magnets has been focused mainly on the search for materials with large anisotropies, mainly based on rare-earth elements, e.g., SmCo 5 or Fe 14 Nd 2 B [42,[357][358][359][360][361][362][363][364][365]. However, the ever increasing demand for permanent magnets has triggered a shortage of rare-earth raw materials resulting in a significant increase in price.…”

Section: Permanent Magnetsmentioning

confidence: 99%

“…The recent patents filed in this topic can be divided in three different categories: (i) the ones based on rare-earth hard magnets (FeNdB or SmCo) coupled to high moment soft magnets such as Fe or FeCo [ [47][48][49][50][51][52][53][54][55][56][57][58] (ii) nanoparticles of hard magnets based on precious metals (e.g., FePt or FePd) coupled to Fe, Fe 3 Pt, Fe 3 O 4 or FeCo [54,55,[59][60][61][62][63]and (iii) novel structures based on rare-earth and precious-metals free hard magnets (-Fe 2 O 3 , MnAl, MnBi, Ba-ferrite or Co 3 C), coupled to soft materials (e.g., Fe, FeCo, FeNi or Co 2 C) [53][54][55][65][66][67][68][69][70][71]. Although most of the proposed systems are based on conventional structures, i.e., where the hard magnet is in the core, some notable exceptions are Fe/-Fe 2 O 3 and Co/Co 3 C which, since the hard magnet is obtained by the surface treatment of the core, they have an inverse soft/hard structure [66,71].…”

Section: Permanent Magnetsmentioning

confidence: 99%

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Applications of exchange coupled bi-magnetic hard/soft and soft/hard magnetic core/shell nanoparticles

et al. 2015

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A B S T R A C TThe applications of exchange coupled bi-magnetic hard/soft and soft/hard ferromagnetic core/shell nanoparticles are reviewed. After a brief description of the main synthesis approaches and the core/shell structural-morphological characterization, the basic static and dynamic magnetic properties are presented. Five different types of prospective applications, based on diverse patents and research articles, are described: permanent magnets, recording media, microwave absorption, biomedical applications and other applications. Both the advantages of the core/shell morphology and some of the remaining challenges are discussed.

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Section: Permanent Magnetsmentioning

confidence: 99%

Section: Permanent Magnetsmentioning

confidence: 99%

Applications of exchange coupled bi-magnetic hard/soft and soft/hard magnetic core/shell nanoparticles

et al. 2015

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“…This concept of exchange coupling brought a new hope for the improvement of (BH) max of permanent magnets [47][48][49][50][51][52][53]. For an efficient exchange coupling, the characteristic dimension of the soft phase cannot exceed about twice the wall thickness of magnetic domains in the hard phase, which typically limits the size of the soft grains to ~10 nm, and the volume fraction of the soft phase must not be too high in order to lose a large H c value, which limits the (BH) max of the composite [50][51][52].…”

Section: Magnetic Properties Of Nanoparticle Compositesmentioning

confidence: 99%

Prospects for nanoparticle-based permanent magnets

et al. 2012

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“…In broad strokes, they concluded that the requirements for improving the BH max through exchange-coupling are (i) an intimate contact between the two phases and (ii) a soft phase with crystallite sizes below a certain limit, usually on the order of a few tens of nanometers. 7,8 …”

Section: Introductionmentioning

confidence: 99%

Approaching Ferrite-Based Exchange-Coupled Nanocomposites as Permanent Magnets

Granados-Miralles

Saura-Múzquiz

Andersen

et al. 2018

ACS Appl. Nano Mater.

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During the past decade, CoFe2O4 (hard)/Co–Fe alloy (soft) magnetic nanocomposites have been routinely prepared by partial reduction of CoFe2O4 nanoparticles. Monoxide (i.e., FeO or CoO) has often been detected as a byproduct of the reduction, although it remains unclear whether the formation of this phase occurs during the reduction itself or at a later stage. Here, a novel reaction cell was designed to monitor the reduction in situ using synchrotron powder X-ray diffraction (PXRD). Sequential Rietveld refinements of the in situ data yielded time-resolved information on the sample composition and confirmed that the monoxide is generated as an intermediate phase. The macroscopic magnetic properties of samples at different reduction stages were measured by means of vibrating sample magnetometry (VSM), revealing a magnetic softening with increasing soft phase content, which was too pronounced to be exclusively explained by the introduction of soft material in the system. The elemental compositions of the constituent phases were obtained from joint Rietveld refinements of ex situ high-resolution PXRD and neutron powder diffraction (NPD) data. It was found that the alloy has a tendency to emerge in a Co-rich form, inducing a Co deficiency on the remaining spinel phase, which can explain the early softening of the magnetic material.

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Exchange-Coupled Nanocomposite Permanent Magnets

Cited by 32 publications

References 82 publications

Applications of exchange coupled bi-magnetic hard/soft and soft/hard magnetic core/shell nanoparticles

Applications of exchange coupled bi-magnetic hard/soft and soft/hard magnetic core/shell nanoparticles

Prospects for nanoparticle-based permanent magnets

Approaching Ferrite-Based Exchange-Coupled Nanocomposites as Permanent Magnets

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