A magnetically-guided catheter 100 includes a tip positioning magnet in the distal electrode assembly configured to interact with externally applied magnetic fields for magnetically-guided movement. A magnetically-guided mapping catheter 100 includes an electrically-conductive capsule in the form of a casing 146 that includes a distal ablation surface and isolates the positioning magnet from bio-fluids to prevent corrosion. An open irrigation ablation catheter includes an isolated manifold that isolates the positioning magnet from contact with irrigation fluid to prevent corrosion.