Nanoscale Magnetic Texture Induced by Exchange Bias: Insights from NV Magnetometry

Exchange bias, originating at the interface between ferromagnetic and antiferromagnetic layers, plays a pivotal role in spintronic devices such as magnetic tunnel junctions (MTJs) because it stabilizes the magnetization direction of one electrode, often the reference magnetic layer, enabling controlled switching behavior. In this study, we combine macroscopic magnetometry with nanoscale magnetic imaging using nitrogen-vacancy (NV) centers in diamond to investigate the local magnetic texture induced by exchange bias. NV magnetometry offers high-resolution, noninvasive mapping of stray magnetic fields under ambient conditions. To interpret the experimental data, we perform micromagnetic simulations incorporating a granular anisotropy landscape. This approach successfully reproduces both the hard-axis magnetization loop and the spatial distribution of stray fields observed experimentally. From these results, we extract the dispersion of magnetization angles (ripple angle) and extrapolate the coupling field values between MTJ electrodes, attributed to the observed spin texture.