In-situ Lorentz microscopy of Fe85Si2B8P4Cu1 nanocrystalline soft magnetic alloys

•Magnetic properties of newly developed Fe–Si–B–P–Cu nanocrystalline alloys are analyzed by TEM.•Motion of magnetic domain walls were visualized by in-situ Lorentz microscopy.•Borides (Fe2B) in heat-treated specimen cause reduction in domain wall motion smoothness.

Microstructure dependence of magnetic properties of soft magnetic Fe–Si–B–P–Cu nanocrystalline alloys were studied by using in-situ Lorentz microscopy in a transmission electron microscope equipped with a magnetizing system. In particular, we investigated in detail motion of magnetic domain walls in heat-treated Fe85Si12B6P4Cu1 amorphous ribbons. Smooth motion of domain walls was observed for the optimally heat-treated (at 430 °C) nano-crystalline alloy. Pinning of domain walls was observed for higher-temperature-heat-treated (470 °C) ribbons. Both ribbons showed a nanocrystalline structure containing α-Fe crystallites of about 15 nm in size. Electron diffraction patterns indicated that the higher-temperature-heat-treated samples contained boride precipitates, which is considered to cause less smooth domain wall motion.