: This study develops a high-reliability, power-off electromagnetic brake for heavy-duty AGV/AMR systems, driven by increasing logistics automation and carbon neutrality goals. We designed the brake, optimizing geometric parameters via FEM-based electromagnetic analysis (Ansys Maxwell 2D) to minimize magnetic saturation. For structural vibration stability, we conducted component-level modal tests and FEM-based complex eigenvalue analysis (ABAQUS/Standard 2024) to analyze unstable modes under varying friction coefficients. Our analysis identified mode coupling between the armature's out-of-plane modes as the main cause of vibration instability. Notably, the optimized design (a = 12 mm, b = 13 mm) successfully eliminated unstable modes at the reference friction coefficient (μ = 0.3). This research proposes a design direction and reliability methodology for high-performance brakes suited for heavy-load logistics robots.