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.
Highlights
Nanocrystalline Sm-Co alloys possess large coercivity due to the pinning of domain walls by the nanograin boundaries.[1,2] Intensive milling and subsequent annealing have been used to produce nanocrystalline Sm-Co magnets.[3,4,5] the magnets are usually obtained in the form of randomly oriented powders with relatively low remanence due to magnetic isotropy
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
Anisotropic SmCo5 nanoflake powders prepared by high energy ball milling (HEBM) process approached coercivity values as high as 21 kOe
Summary
Nanocrystalline Sm-Co alloys possess large coercivity due to the pinning of domain walls by the nanograin boundaries.[1,2] Intensive milling and subsequent annealing have been used to produce nanocrystalline Sm-Co magnets.[3,4,5] the magnets are usually obtained in the form of randomly oriented powders with relatively low remanence due to magnetic isotropy. Crystallographically textured SmCo5 and SmCo7 nanoflakes were prepared by surfactant-assisted high energy ball milling (HEBM).[8,9,10] The SmCo5 nanoflakes have attractive magnetic properties; coercivity of up to kOe and maximum energy product of up to MGOe.[9] the nanoflake powders possess a potential to fabricate anisotropic nanocrystalline SmCo5 bulk magnets with higher magnetization and higher coercivity. Anisotropic nanocrystalline SmCo7 bulk magnets created from nanoflake powders via spark plasma sintering technique were investigated by several researchers.[10,11] it is less reported on correlation between nanoflake morphology and final properties of the SmCo5 bulk magnets. We prepared SmCo5 nanoflakes by surfactant-assisted high energy ball milling and fabricated SmCo5 bulks from these powders by induction hot-pressing. The effect of the flake thickness on coercivity of the powder itself and bulks was investigated
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