ABSTRACTWe conducted the in-situ observations of the magnetic domain structure change in
Nd-Fe-B magnets at high temperature by transmission electron microscopy (TEM) /
Lorentz microscopy with applying an external magnetic field. Prior to
observation, a thin foil was magnetized by an external magnetic field of 2.0 T
to almost saturation, then the magnetic domain structures were observed by the
Fresnel mode with in-situ heating. At 225°C, reverse magnetic domains
were found to generate in the thin foil sample without applying an external
magnetic field. When we applied a magnetic field on the same direction to the
pre-magnetization direction at 225°C, one magnetic domain wall was
pinned by a grain boundary and the other magnetic domain wall moved. As the
results, the reverse magnetic domain shrank then annihilated. When we cut the
applied magnetic field, the reverse magnetic domain generated at almost the same
location. On the other hand, when we applied a magnetic field to the foils in
the opposite direction, the reverse domain started to grow, i.e., magnetic
domain walls started to move. The observation results of the shrink or growth of
the reverse domain showed that the pinning effect of grain boundary against
domain wall motion would be different depending on the applied magnetic field
direction. Moreover, domain walls was observed to be pinned by grain boundaries
at elevated temperature, so that the coercivity of Nd-Fe-B magnet would occur by
pinning mechanism.
Variation of the Magnetic Domain and GMI Property of a HFC-Type Magnetic Field Sensor with Inclined Domain Walls Resulting from the Application of an External Magnetic Field in the Measurement Direction
