Structural analysis of nanocrystals and their role in the coercivity mechanism of Nd–Fe–Al–Dy bulk amorphous ferromagnets

Tan, Xiaohua; Collocott, S.J.; Liu, Hong Wei; Xiong, Xiang‐Yuan; Xu, Hui

doi:10.1016/j.jmmm.2013.04.055

Cited by 9 publications

(2 citation statements)

References 27 publications

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“…The result indicates that the domain wall width decreases with the Al substitution. It is worthy of noting that the domain wall width is similar to the size of the dHCP Nd nanocrystals observed in the TEM results, which indicates that the dHCP Nd can act as the pinning center of the domain wall, which is also suggested by Tan et al [13,14] .…”

Section: B Magnetic Properties and Coercivity Mechanismsupporting

confidence: 81%

Magnetic Characteristics for the Mould-Cast Hard Magnetic Nd_70–xFe₃₀Al_x ($x=0$ –10) Alloys

et al. 2015

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Bulk amorphous or nanocrystalline Nd-Fe based alloys show surprising hard magnetic properties. Its pronounced room temperature coercivity results from the high random anisotropy of ferromagnetic nanoclusters. In this work, the magnetic characteristics of the mould-cast Nd70-xFe30Alx (x=0-10) alloys were studied in details. The substitution of Nd by Al could improve the glass forming ability, reduce the coercivity and Curie temperature, and suppress the formation of Nd2Fe17 phase. The microstructure consisting of 5-20 nm sized dHCP Nd phases embedded in the amorphous phase was evident. The room temperature coercivities decreased from 340 to 270 kA/m with increasing Al content. The domain structure was investigated by magnetic force microscopy. The temperature dependence of the coercivity could be well explained by the strong pinning model of domain walls of Gaunt. The dHCP Nd phase works as the pinning center. The Hopkinson peak was also investigated using the mathematical formalism based on the Stoner-Wohlfarth model. The hard magnetic properties of the alloys disappeared after heat treatment at 873K since part of the amorphous phase and the ferromagnetic clusters transferred into Th2Zn17-type phases and some unknown phase. This work provides further insights into the origin of the hard magnetism for the amorphous and nanocluster alloys.Index Terms-Magnetic clusters, Strong pinning model, Hopkinson effect. 0018-9464 (c)

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Section: B Magnetic Properties and Coercivity Mechanismsupporting

confidence: 81%

Magnetic Characteristics for the Mould-Cast Hard Magnetic Nd_70–xFe₃₀Al_x ($x=0$ –10) Alloys

et al. 2015

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“…It is of interest to note that, although the term amorphous is used, the common feature of the microstructure in Nd-based BAAs is the presence of clusters or nanocrystals, which vary in diameter from 1.2 nm to 20 nm, embedded in an amorphous matrix in these materials151617181920. Despite much effort, the mechanism leading to the hard magnetic behavior of Nd-based bulk amorphous alloys is still under hot debate.…”

mentioning

confidence: 99%

Combined effects of magnetic interaction and domain wall pinning on the coercivity in a bulk Nd60Fe30Al10 ferromagnet

Tan

Chan

Han

et al. 2014

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Understanding the coercivity mechanism has a substantial impact on developing novel permanent materials. However, the current coercivity mechanisms used widely in permanent alloys cannot explain well the amorphous phase produced hard magnetic behavior of Nd-based bulk amorphous alloys (BAAs). Here, we propose that the coercivity in as-cast Nd 60 Fe 30 Al 10 alloy is from the combination of magnetic interaction and strong pinning of domain walls. Moreover, the role of domain wall pinning is less affected after crystallization, while the magnetic interaction is dependent on the annealing temperature. Our findings give further insight into the coercivity mechanism of Nd-based bulk ferromagnets and provide a new idea to design prospective permanent alloys with coercivity from the combination of magnetic interaction and pinning of domain walls.P ermanent magnets are fundamental to the technological success in electric machines, and have found applications in a wide range of devices due to their unique ability to deliver magnetic flux into the air gap of a magnetic circuit without continuous expenditure of energy 1 . A breakthrough came in 1984 with a discovery of Nd 2 Fe 14 B phase when Croat et al and Sagawa et al were able to obtain large coercivity (H c ) in Nd-Fe-B alloys by using melt-spinning and powder metallurgy technique, respectively 2-4 . Since then, Nd-Fe-B magnets with a maximum energy product ((BH) max ) over 450 kJ/m 3 have been exploited and 90% of the limit for the (BH) max can be produced commercially in sintered Nd-Fe-B magnets 5 . However, it appears that the search for novel hard magnetic materials with higher (BH) max , has somewhat stagnated and no further breakthrough is in sight. Understanding the coercivity mechanism has a substantial impact on developing novel permanent materials. Three important coercivity mechanisms were used widely in permanent magnets. Nucleation of domain model demonstrates that the nucleation of reverse domains is at surface irregularities and defects with low anisotropy 6,7 . It has been used effectively in sintered Nd 2 Fe 14 B, SmCo, bonded BaFe 12 O 19 and Sm 2 Fe 17 N 3 magnets 8 . The domain wall pinning model shows that the inhomogeneities present in the sample can prevent domain wall motion resulting in high coercivity 9,10 . It has been an important coercivity mechanism in Sm 2 Co 17 -based magnets and melt-spun Nd 2 Fe 14 B alloys 8 . 'Exchange hardening' illustrates that a reasonable high coercivity is obtained resulting from an increase of the nucleation field by the exchange coupling between soft and hard magnetic phase in nanocomposite alloys 11,12 . However, the above three models cannot explain well the amorphous phase produced hard magnetic behavior of Nd-based bulk amorphous alloys (BAAs).Since the Nd 60 Fe 30 Al 10 bulk amorphous alloy was first reported in 1996 13,14 , Nd-Fe-Al based BAAs have been growing interest because of exceptional hard magnetic property at room temperature. It is of interest to note that, although the term amorphous is used,...

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Magnetic properties of amorphous metallic alloys

Stachurski¹,

Wang²,

Tan³

2021

An Introduction to Metallic Glasses and Amorphous Metals

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Structural analysis of nanocrystals and their role in the coercivity mechanism of Nd–Fe–Al–Dy bulk amorphous ferromagnets

Cited by 9 publications

References 27 publications

Magnetic Characteristics for the Mould-Cast Hard Magnetic Nd_70–xFe₃₀Al_x ($x=0$ –10) Alloys

Magnetic Characteristics for the Mould-Cast Hard Magnetic Nd_70–xFe₃₀Al_x ($x=0$ –10) Alloys

Combined effects of magnetic interaction and domain wall pinning on the coercivity in a bulk Nd60Fe30Al10 ferromagnet

Magnetic properties of amorphous metallic alloys

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Structural analysis of nanocrystals and their role in the coercivity mechanism of Nd–Fe–Al–Dy bulk amorphous ferromagnets

Cited by 9 publications

References 27 publications

Magnetic Characteristics for the Mould-Cast Hard Magnetic Nd70–xFe30Alx ($x=0$ –10) Alloys

Magnetic Characteristics for the Mould-Cast Hard Magnetic Nd70–xFe30Alx ($x=0$ –10) Alloys

Combined effects of magnetic interaction and domain wall pinning on the coercivity in a bulk Nd60Fe30Al10 ferromagnet

Magnetic properties of amorphous metallic alloys

Contact Info

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About

Magnetic Characteristics for the Mould-Cast Hard Magnetic Nd_70–xFe₃₀Al_x ($x=0$ –10) Alloys

Magnetic Characteristics for the Mould-Cast Hard Magnetic Nd_70–xFe₃₀Al_x ($x=0$ –10) Alloys