Magneto-haptics is a design approach of haptic sensations powered by the forces present among permanent magnets during active touch. Magnetic force has not been efficiently explored in haptic design because it is not intuitive and there is a lack of methods to associate or visualize magnetic force with haptic sensations, especially for complex magnetic patterns. To represent the haptic sensations of magnetic force intuitively, magneto-haptics formularizes haptic potential from the distribution of magnetic force along the path of motion. It provides a rapid way to compute the relationship between the magnetic phenomena and the haptic mechanism. Thus, we can convert a magnetic force distribution into a haptic sensation model, making the design of magnet-embedded haptic sensations more efficient. We demonstrate three applications of magneto-haptics through interactive interfaces and devices. We further verify our theory by evaluating some magneto-haptic designs through experiments.