Insights into the micro magnetic loss mechanism of microwave absorption by off-axis electron holography

High permeability and high saturation magnetization are two key attributes to strong microwave absorption for magnetic loss composites, which depend on the chemical composition, particle size, surface profile, fabrication method, etc. However, it is still a challenge to understand the influences of these properties on micro magnetic behaviors to manipulate microwave absorption performances. In this study, magnetic absorbers with spherical and flaky shapes were adapted to investigate the influences of morphology on magnetic properties via off-axis electron holography. Stray magnetic flux lines were visualized to validate the difference in the forms of magnetic incorporation among spherical and flaked-shaped metallic particles, which then results in reflection loss (RL) up to -53 dB for the flakes and absorption ( > 99%) bandwidth up to 3 GHz for the spherical types. The micro-field detection using the powerful technique of off-axis electron holography sheds new light on the understanding about intrinsic magnetic micro behaviors for metallic composites.