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

Abstract

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,...

Magnetotransport and magnetic properties of amorphous $$\mathrm{NdNi}_5$$ thin films

“…4 c. At K both and show a change in the slope but they remain significantly different from zero up to 70 K. The positive inflexion in suggests an additional moment which can potentially come from nanoscale magnetic clusters having a low . This is consistent with the rise in below K, as the onset of magnetic particles is likely to enhance pinning of domain walls, as reported also for amorphous films 35 . Even not clearly visible, due to a small remanent moment trapped in the superconducting magnet, the value of H c turns out to be negative for K. The low-temperature value of , measured at K, is almost one third smaller then those reported in the literature for polycrystalline samples 7 , 8 , 11 and it does not significantly depend on d .…”

High coercivity SmCo5 synthesized with assistance of colloidal SiO2

“…5 , and the important magnetic properties are extracted and listed in Table 1 . The initial magnetization curves reveal three stages during the magnetizing process: (I) fast magnetization changes caused reversible domain wall displacements under low applied magnetic field; (II) when continually increasing the magnetic field, the magnetization changes slow down, this is interpreted as pinning sites causing irreversible domain wall displacements; (III) the magnetization increases gradually with increased applied magnetic field, here rotation of the magnetic moment in SSD particles takes place, this requires high magnetic fields to overcome the energy barrier from preferred orientation and shape anisotropy 23 – 26 . SmCo 5 particles cannot be saturated completely at the maximum applied magnetic field (9 T) at the PPMS system at Aarhus University.…”

Data-driven magneto-elastic predictions with scalable classical spin-lattice dynamics

“…Despite the critical role of magnetism in the aforementioned materials classes, modeling efforts to study the interplay between structural and magnetic properties have been notably lacking. Furthermore, there are unanswered scientific questions regarding the significance of magnetism in matter that is shock-compressed 10,11 or exposed to strong electromagnetic fields such as in coherent lights sources 12,13 , pulsed power and high magnetic fields facilities 14,15 . Properties of interest include phase transitions, thermal stability of magnetic defects, magneto-mechanical couplings, but many of these subjects are challenging or prohibited by state of the art computational tools.…”