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This paper presents structural topology optimization of an electro/permanent magnet linear actuator. The optimization goal is to maximize the average magnetic force acting on a plunger that travels over a distance of 20 mm. To achieve this goal, the magnetic field sources (i.e., permanent magnet, positive and negative direction coils), and ferromagnetic material of the yoke are simultaneously co-designed using four design variables for each finite element. The magnetic force is calculated using the Maxwell stress tensor method coupled with finite-element analysis. The optimization sensitivity analysis is performed using the adjoint method, and the optimization problem is solved using a sequential linear programming method. To illustrate the utility of the proposed design approach, linear actuators are designed, and the optimal shapes and locations of the yoke permanent magnet, coils, and ferromagnetic part are provided. In addition, the effects of the PM magnetization direction and the current density strength on design results are described.