<i>Ex situ</i> synthesis of magnetically exchange coupled SrFe12O19/Fe-Co composites

Xu, Xia; Hong, Yang‐Ki; Park, Jihoon; Lee, Woncheol; Lane, Alan M.

doi:10.1063/1.4944703

Cited by 15 publications

(7 citation statements)

References 28 publications

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“…3 a). Regardless of the quantity of Ca-substitution in the Sr-ferrite, all hysteresis loops showed single-phased ferromagnetic behavior without kinks, even though a small amount of the antiferromagnetic Fe 2 O 3 phase was incorporated in the samples with x ≥ 0.30 31 . Fig.…”

Section: Resultsmentioning

confidence: 95%

Anisotropic characteristics and improved magnetic performance of Ca–La–Co-substituted strontium hexaferrite nanomagnets

Lee

Hwang

et al. 2020

Sci Rep

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Recent studies on next-generation permanent magnets have focused on filling in the gap between rare-earth magnets and rare-earth-free magnets, taking into account both the cost-effectiveness and magnetic performance of the magnetic materials. As an improved rare-earth-free magnet candidate, here, Ca-substituted M-type Sr-lean hexaferrite particles within a nano- to micro-scale regime, produced using an ultrasonic spray pyrolysis method, are investigated. Theoretically, the maximum coercivity (Hc) can be achieved in submicron Sr-ferrite crystals (i.e., 0.89 μm). The plate-like resultants showed a significant enhancement in Hc, up to a record high of 7880.4 Oe, with no deterioration in magnetization (M: 71–72 emu/g). This resulted in more favorable magnetic properties than those of the traditional Sr–La–Co ferrites. On the basis of microstructural analysis and fitting results based on the law of approach to saturation method, the Ca-substitution effects on the change in size and anisotropic characteristics of the ferrite particles, including pronounced lateral crystal growth and a strong increase in magnetocrystalline anisotropy, are clearly demonstrated. The cost-effective, submicron, and Ca-substituted Sr-ferrite is an excellent potential magnet and moreover may overcome the limitations of traditional hard magnetic materials.

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Section: Resultsmentioning

confidence: 95%

Anisotropic characteristics and improved magnetic performance of Ca–La–Co-substituted strontium hexaferrite nanomagnets

Lee

Hwang

et al. 2020

Sci Rep

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“…Many efforts have been made to synthesize exchange-spring nanomagnets using different ex situ approaches including conventional physical techniques such as mechanical mixing with individual magnetic powder, − self-assembly, − and electroless deposition of a soft magnet on a hard magnet. − Such magnetic composites commonly possess a predominance of a long-range dipolar interaction of the hard–hard and soft–soft magnetic phases based on the uneven coupling between the hard and soft magnetic phases, resulting in enervating the exchange-coupling interaction and further deteriorating magnetic performance . Moreover, even the use of mechanical power for powder mixing or a strong acidic solution for electroless coatings causes fast oxidation of the metallic magnets and, at worst, phase decomposition into a nonmagnetic phase because metal magnets are vulnerable to harsh process conditions …”

Section: Introductionmentioning

confidence: 99%

Phase- and Composition-Tunable Hard/Soft Magnetic Nanofibers for High-Performance Permanent Magnet

Lee

Hwang

et al. 2020

ACS Appl. Nano Mater.

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An exchange-spring magnet is a next-generation permanent magnetic model that possesses a synergistic effect of single-phased hard and soft magnets, thereby giving rise to enhanced magnetic performance. However, in spring magnet preparation thus far, it has remained a challenge to manipulate the magnetic properties via the exchange-coupling effect due to the lack of a synthetic method that enables the hard/soft interfacial magnetic interaction in a homogeneous manner. Here, we report an in situ approach for the synthesis of a phase-and composition-tunable SmCo-based spring magnet based on a binary phase system. This is the first reported systematic and prospective approach to spring magnet preparation. An electrospinning technique with the use of a composition-tunable precursor enables the fabrication of bimagnetic nanofibers with a precisely controlled hard/soft magnet volume ratio (0 to 100%) and a good number of interfacial sites, leading to an effective magnetic coupling interaction. On the basis of a microstructural study and qualitative magnetic measurements, we demonstrate an enhancement in magnetic performance for binary-phased fibers and clearly manifest the elucidation of the exchange-coupling effect between nanograins across the interface in the one-dimensional nanomagnet. We envision that this work can provide a potential approach to develop exchange-coupled spring magnet and moreover, offering an ideal model to understand the nanomagnetism of a well-constructed one-dimensional spring nanostructure.

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“…According to previous studies, the magnetic characteristics for exchange-coupling must fulfill the following conditions: (i) a smooth single-phase hysteresis curve without kinks or shoulders, (ii) M r should be much higher than that for the individual hard phase, (iii) M r / M s > 0.5 for a randomly oriented easy axis following the Stoner–Wohlfarth theory, and (iv) ( BH ) max enhancement compared with the single hard phase. − Up to 15 min of plating time, all obtained samples meet the conditions for exchange coupling: their hysteresis curves showed a single-phase-like magnetization behavior. Simultaneous enhancements in M r and in ( BH ) max were achieved as well.…”

Section: Resultsmentioning

confidence: 85%

Exchange-Coupling Interaction in Zero- and One-Dimensional Sm₂Co₁₇/FeCo Core–Shell Nanomagnets

Lee¹,

Kim

et al. 2019

ACS Appl. Mater. Interfaces

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Rare-earth-based core–shell spring nanomagnets have been intensively studied in the permanent magnet industry. However, the inherent agglomeration characteristics of zero-dimensional (0-D) magnetic nanoparticles are an issue in practical fabrication of magnetic nanocomposites due to deterioration in exchange-coupling interactions, resulting in inferior magnetic performance. Here, with an aim to overcome the structural limitations, we report a new type of SmCo/FeCo core–shell nanomagnet with a well-dispersed one-dimensional (1-D) structure prepared by a combination of electrospinning and electroless plating processes. An FeCo layer with a tailored thickness on nanoscale SmCo was produced to achieve a sufficient exchange-coupling effect. The influence of electroless plating time on the microstructure of fibers was discussed, and comparisons were made as a function of the magnet shape. A 1-D SmCo/FeCo spring nanomagnet having a core diameter ranging from 150 to 200 nm and a shell thickness of 15–20 nm showed a potent exchange-coupling effect compared with its 0-D counterpart. This effectively reduced self-aggregation and further showed a remarkable enhancement in (BH)max (above 45.7%). We think that this novel structure marks a new era in the exchange-spring magnet industry and may overcome the limitations of traditional core–shell nanomagnets.

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Ex situ synthesis of magnetically exchange coupled SrFe12O19/Fe-Co composites

Cited by 15 publications

References 28 publications

Anisotropic characteristics and improved magnetic performance of Ca–La–Co-substituted strontium hexaferrite nanomagnets

Anisotropic characteristics and improved magnetic performance of Ca–La–Co-substituted strontium hexaferrite nanomagnets

Phase- and Composition-Tunable Hard/Soft Magnetic Nanofibers for High-Performance Permanent Magnet

Exchange-Coupling Interaction in Zero- and One-Dimensional Sm₂Co₁₇/FeCo Core–Shell Nanomagnets

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Ex situ synthesis of magnetically exchange coupled SrFe12O19/Fe-Co composites

Cited by 15 publications

References 28 publications

Anisotropic characteristics and improved magnetic performance of Ca–La–Co-substituted strontium hexaferrite nanomagnets

Anisotropic characteristics and improved magnetic performance of Ca–La–Co-substituted strontium hexaferrite nanomagnets

Phase- and Composition-Tunable Hard/Soft Magnetic Nanofibers for High-Performance Permanent Magnet

Exchange-Coupling Interaction in Zero- and One-Dimensional Sm2Co17/FeCo Core–Shell Nanomagnets

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Exchange-Coupling Interaction in Zero- and One-Dimensional Sm₂Co₁₇/FeCo Core–Shell Nanomagnets