Determination of magnetic flux density at the nanometer-scale antiphase boundary in Heusler alloy Ni50Mn25Al12.5Ga12.5

Understanding magnetic degradation in interface regions is important for materials science and technologies. An essential problem is the significant depression of ferromagnetism observed in an antiphase boundary (APB), which induces material functionalities/anomalies such as pinning of magnetic domain walls, etc. However, magnetization analysis on APB remains challenging due to the difficulty of collecting magnetic information from such a nanometer-scale interface region. We here use electron holography in order to obtain magnetic information from the narrow APB region in a Heusler alloy Ni50Mn25Al12.5Ga12.5. The magnetic flux density in APB (∼5.6 nm in breadth) was determined at 0.04 T, and was only 12% of the value for the APB-free matrix. This magnetic depression could be explained by atomic disordering in the APB region, ascertained by high-resolution atomic-column imaging. It is expected that our microscopic approach can be used to understand anomalous interface magnetism observed in various magnetic compounds and/or spin devices.