Deviations from Wohlfarth's remanence relationship in NdFeB magnets

Müller, K.‐H.; Eckert, D.; Handstein, A.; Nothnagel, P.

doi:10.1016/0304-8853(92)90538-y

Cited by 9 publications

(11 citation statements)

References 6 publications

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“…The Wohlfarth relationship [4,8,17] between remanent magnetization M r (H ) and demagnetization remanence M d (H ) has been widely used for study of interaction between magnetic particles and grains. The deviation of demagnetization remanence M d (H ) from the demagnetization remanence calculated from the Wohlfarth model is expressed as below:…”

Section: Demagnetization Processesmentioning

confidence: 99%

A magnetic study of melt-spun ribbons

Ding

Lee

1998

J. Phys.: Condens. Matter

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The structural and magnetic properties of Nd 10 Fe 85 B 5 ribbons produced by meltspinning and subsequent annealing have been studied in this work. A mixture of Nd 2 Fe 14 B and 13 vol.% of Fe was found in the ribbon melt-spun at 30 m s −1 and in samples subsequently annealed. 57 Fe-Mössbauer spectroscopy was used for phase analysis and for study of remanence enhancement. Remanence enhancement was found in ribbons after optimized treatment, after which ribbons consisted of 20-30 nm grains of Nd 2 Fe 14 B and Fe phases. The remanence enhancement effect was attributed to both the soft and hard phases. Demagnetization processes have been studied. All samples exhibited single-phase behaviour, i.e. irreversible demagnetization processes of the hard and soft phases were synchronous even for samples consisting of sub-micron grains. No significant evidence of exchange-spring magnet behaviour was found for samples after optimum treatment. The exchange-spring magnet behaviour was observed in samples annealed at higher temperatures, at which the mean grain sizes were significantly larger than the domain wall thickness of Fe. The magnetic properties of Nd 10 Fe 85 B 5 ribbons in this work were associated with separation of soft Fe grains by Nd 2 Fe 14 B grains because of a low fraction of Fe.

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Section: Demagnetization Processesmentioning

confidence: 99%

A magnetic study of melt-spun ribbons

Ding

Lee

1998

J. Phys.: Condens. Matter

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“…[7][8][9] These materials have some unique characteristics, such as the occurrence of both, positive and negative deviations of the demagnetization remanent magnetization from the Wohlfarth model. [10][11][12] A supporting analysis can provide further insight into the mechanism of exchange coupling between magnetic spins across grain boundaries. 2,13 Recently, nanocrystalline SmCo-based magnets have received considerable attention since both SmCo 5 and Sm 2 Co 17 have higher Curie temperatures than other rareearth-transition metal compounds used for permanents magnets and have many potential high-temperature applications.…”

Section: Introductionmentioning

confidence: 99%

Microstructure and magnetization reversal in nanocomposite SmCo5/Sm2Co17 magnets

Yan

Bollero

Gutfleisch

et al. 2002

Journal of Applied Physics

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A comparative investigation has been made of the microstructure and magnetization reversal behavior of nanocomposite SmCo 5 /Sm 2 Co 17 powders prepared by intensive milling and subsequent annealing. It was found that the saturation magnetization increases monotonically with the increase of the volume fraction of Sm 2 Co 17 at the expense of the coercivity. However, the remanence and the energy product first increase and then decrease with further increase of the fraction of Sm 2 Co 17 . The highest remanence of 0.72 T and energy product of 78 kJ/m 3 are obtained in the powders with 80% and 60% Sm 2 Co 17 , respectively. All the hysteresis loops exhibit a magnetically single-phase behavior. X-ray diffraction results reveal that the coexistence of two phases is found in the mixture of SmCo 5 /Sm 2 Co 17 powders. The demagnetization processes of the SmCo 5 /Sm 2 Co 17 powders are similar to those of nanocomposites consisting of hard and soft phases, in which the exchange-spring magnet behavior was observed. Positive as well as negative deviations in Wohlfarth's remanence analysis ͑␦M -plot͒ have been observed, indicating complex magnetic interactions in these materials.

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“…Isotropic hard magnetic materials with remanence enhancement (remanence greater than 50% of the saturation magnetization) are interesting candidates for economical permanent magnets [1][2][3][4]. Remanence enhancement has been observed in many systems, mainly in nanocrystalline mixtures of hard and soft phases such as Nd 2 Fe 14 B/Fe [3,5,6], Nd 2 Fe 14 B/Fe 3 B [1,7], Sm 2 Fe 17 N 2.7 /Fe [4] and Sm-(Co,Fe) [8,9]. Kneller and Hawig [10] have proposed that the remanence enhancement can be explained in terms of exchange coupling between spins in grain boundary areas of soft and hard phases (called the exchange-spring mechanism [4,6,7,10]).…”

Section: Introductionmentioning

confidence: 99%

“…Remanence enhancement has been observed in many systems, mainly in nanocrystalline mixtures of hard and soft phases such as Nd 2 Fe 14 B/Fe [3,5,6], Nd 2 Fe 14 B/Fe 3 B [1,7], Sm 2 Fe 17 N 2.7 /Fe [4] and Sm-(Co,Fe) [8,9]. Kneller and Hawig [10] have proposed that the remanence enhancement can be explained in terms of exchange coupling between spins in grain boundary areas of soft and hard phases (called the exchange-spring mechanism [4,6,7,10]). Several modelling works [11][12][13][14] have recently shown that exchange coupling of magnetic spins in grain boundaries can result in remanence enhancement, if the grain size is small enough (of the order of the domain wall thickness).…”

Section: Introductionmentioning

confidence: 99%

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A comparative study of melt-spun ribbons of Nd₁₂Fe₈₂B₆and Nd₁₅Fe₇₇B₈

Ding¹,

Li²,

Yong³

1998

J. Phys. D: Appl. Phys.

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This work has shown that isotropic single-phase materials can exhibit remanence enhancement due to exchange coupling between spins in grain boundary areas. Magnetic materials with remanence enhancement are required to have nanocrystalline structures with grain sizes comparable to the domain-wall thickness. The presence of non-magnetic phases may result in de-coupling of magnetic grains, therefore leading to an increase in coercivity but a decrease in remanence. The demagnetization processes of single-phase materials with enhanced remanence are different from those of nanocomposites consisting of hard and soft phases, in that no exchange-spring magnet behaviour was observed for single-phase ribbons of with a nanocrystalline structure. A negative deviation of the demagnetization remanence from the Wohlfarth model [15] was observed due to exchange coupling.

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Deviations from Wohlfarth's remanence relationship in NdFeB magnets

Cited by 9 publications

References 6 publications

A magnetic study of melt-spun ribbons

A magnetic study of melt-spun ribbons

Microstructure and magnetization reversal in nanocomposite SmCo5/Sm2Co17 magnets

A comparative study of melt-spun ribbons of Nd₁₂Fe₈₂B₆and Nd₁₅Fe₇₇B₈

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Deviations from Wohlfarth's remanence relationship in NdFeB magnets

Cited by 9 publications

References 6 publications

A magnetic study of melt-spun ribbons

A magnetic study of melt-spun ribbons

Microstructure and magnetization reversal in nanocomposite SmCo5/Sm2Co17 magnets

A comparative study of melt-spun ribbons of Nd12Fe82B6and Nd15Fe77B8

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A comparative study of melt-spun ribbons of Nd₁₂Fe₈₂B₆and Nd₁₅Fe₇₇B₈