Effect of flake thickness on coercivity of nanocrystalline SmCo5 bulk prepared from anisotropic nanoflake powder

Abstract

In this study, nanocrystalline SmCo5 bulk magnets were prepared by hot-pressing of nanoflake powders fabricated via surfactant-assisted high energy ball milling. Effect of the flake thickness on magnetic coercivity of the SmCo5 bulk was investigated. Anisotropic SmCo5 nanoflakes with thickness between 100 and 1000 nm were prepared by varying the milling parameter of ball-to-powder weight ratio. XRD analysis revealed that as-milled flake powders possessed nanocrystalline grains with no observable oxide peaks. The coercivity of the flake powders varied between 19.9 and 21.3 kOe for 1000 nm to 100 nm thick flakes, which indicated that the flake thickness in this range had no obvious effect on the coercivity of the powders. However, the coercivity of the bulks showed a strong dependence on the flake thickness. The bulk coercivity value of 10.97 kOe corresponding to the flake thickness of 100 nm, was 80% higher compared to the bulk prepared with the flakes of 1000 nm. XRD results on compacted samples did not show any grain growth, however, Sm2O3 and free Co were detected in SmCo5 bulks and their content increased with reduced flake thickness. Interestingly enough the bulk coercivity was not deteriorated with the presence of Sm oxide and Co.

Unconventional magnetization textures and domain-wall pinning in Sm–Co magnets

“…We have also found that changing the thickness of the SmCo 5 cells does not modify the magnetic performance strongly, in agreement with experiments [31] and theory [32], showing that the pinning field is saturated for a SmCo 5 thickness of more than 4 nm. This contradicts the predictions by Fidler et al [10,12], stating that the SmCo 5 thickness should be at least three times the exchange length (3δ exc ≈ 20 nm) for effective domain-wall pinning.…”

Effect of Microstructure on the Coercivity of SmCo₅ Intermetallic Compound

“…C.H. Chen et al, 29) Y. Shen et al 30) explained that fine lamellar grains improve the coercivity of the final product. Similarly, N.M. Taliyan et al 31) and D.L.L.…”