Effect of grain-boundary diffusion process on the geometry of the grain microstructure of Nd$-$Fe$-$B nanocrystalline magnets

Abstract

Hot-deformed anisotropic Nd$-$Fe$-$B nanocrystalline magnets have been subjected to the grain-boundary diffusion process (GBDP) using a ${\mathrm{Pr}}_{70}{\mathrm{Cu}}_{30}$ eutectic alloy. The resulting grain microstructure, consisting of shape-anisotropic Nd$-$Fe$-$B nanocrystals surrounded by a Pr$-$Cu-rich intergranular grain-boundary phase, has been investigated using unpolarized small-angle neutron scattering (SANS) and very small-angle neutron scattering (VSANS). The neutron data have been analyzed using the generalized Guinier-Porod model and by computing model-independently the distance distribution function. We find that the GBDP results in a change of the geometry of the scattering particles:~In the small-$q$ regime the scattering from the as-prepared sample exhibits a slope of about $2$, which is characteristic for the scattering from two-dimensional platelet-shaped objects, while the GBDP sample manifests a slope of about $1$, which is the scattering signature of one-dimensional elongated objects. The evolution of the Porod exponent indicates the smoothing of the grain surfaces due to the GBDP, which is accompanied by an increase of the coercivity.

6 pages, 4 figures, 1 table

References in corpus (3)

• Dipolar-coupled moment correlations in clusters of magnetic nanoparticles
• Evidence for the formation of nanoprecipitates with magnetically disordered regions in bulk ${\mathrm{Ni}}_{50}{\mathrm{Mn}}_{45}{\mathrm{In}}_5$ Heusler alloys
• Spin structures of textured and isotropic Nd-Fe-B-based nanocomposites: Evidence for correlated crystallographic and spin texture

Cited by in corpus (3)

• Small-angle neutron scattering by spatially inhomogeneous ferromagnets with a nonzero average uniaxial anisotropy
• Unraveling the magnetic softness in Fe-Ni-B based nanocrystalline material by magnetic small-angle neutron scattering
• Magnetic correlations in polycrystalline $\mathrm{T}{\mathrm{b}}_{0.15}\mathrm{C}{\mathrm{o}}_{0.85}$