Magnetic maze in steel resolved by correlative structural analysis

Abstract

Grains in ferritic steel oriented along the hard magnetization axis exhibit complex magnetic structures, often visualized as maze-like patterns using magnetic force microscopy. Although previously observed, their origin has remained unclear. Our study combines correlative structural analysis—including analytical electron microscopy, magnetic force microscopy, magneto-optical Kerr microscopy, and micromagnetic simulations—to reveal the origin of these patterns. Both experiments and simulations confirm that grains aligned with the hard axis show a maze-like domain structure, while other orientations display simpler configurations. Simulations demonstrate that the maze arises from slight out-of-plane magnetization components along the (111) surface, whereas magnetization remains in-plane on the (110) surface due to energy minimization. Notably, maze-like domains are absent when the surface orientation deviates more than 7 degrees from the hard axis. We also identify a critical thickness range (120–256 nm) necessary for maze formation. Dynamic studies show that maze-like patterns disappear if the magnetic field in the vertical direction increases, while the actual domain walls move between pinning sites. Our comprehensive approach provides quantitative validation for a previously qualitative phenomenon, offering new insight into the magnetic behavior of ferritic steel and the measurable influence of crystallographic orientation and sample thickness on domain structure.