Magnetic domain switching and hysteresis loops in a single crystal α-iron with and without nonmagnetic particles were simulated based on the Landau-Lifshitz-Gilbert equation of magnetization dynamics. Both the nonmagnetic particle and the 360° domain wall are nucleation sites of an antidirection domain during domain switching; however, the 360° Bloch domain wall is the easiest nucleation site. The nucleation occurs by splitting the 360° Bloch domain wall into two 180° Bloch domain walls. The existence of nonmagnetic particles could prevent the formation of 360° Bloch domain walls and cause magnetic hardening. Simulations demonstrate the impact of nonmagnetic particle sizes on magnetic domain switching and coercive field.