In-situ lorentz and electron-holography imaging of domain-wall propagation and grain-boundary pinning within anisotropic Nd-Fe-B sintered-magnet thin films

Nucleation of reverse domains from saturated states and the following domain-wall (DW) propagation in electron-transparent anisotropic Nd-Fe-B sintered-magnet specimens (with thickness of 300 to 500 nm) was investigated. The specimens were in-situ imaged by Foucault-mode Lorentz microscopy with a 5-kOe in-plane magnetizing specimen holder. Three types of DW structure were found to play an important role in magnetization reversal: (i) long DWs running across GBs of several grains continuously while propagating perpendicularly to the easy axis; (ii) a pair of 180? Bloch DWs forming a hairpin-shape junction near the GB while propagating parallel to the easy axis; and (iii) zig-zag composition DWs pinned at c-plane GBs. The results of observations by electron holography showed that the magnetization misaligns from the easy axis locally near hairpin tips of head-on DWs when they are pinned on c-plane GBs. Stability of the head-on DW was investigated by micromagnetic simulation. The observed evolution of domains is explained in terms of the pinning fields of the GBs and the nucleation field of the DW, which both depend on surface damage of the specimens.

Automated summary

The investigation delved into the nucleation of reverse domains and domain-wall propagation in anisotropic Nd-Fe-B sintered-magnet specimens. Different types of domain-wall structures play crucial roles in magnetization reversal, with head-on DWs showing lower stability when pinned at c-plane GBs.