Material shielding conditions in the B_wd–P_wd parameter space. DA, DB, and DAZ white dwarfs are denoted as open circles, open circles, and solid circles, respectively. The purple line represents the magnetosphere condition, above which the magnetic effect is active. The vertical lines are the rotational periods where the corotation radius equals the sublimation radius for refractory materials (solid lines) and volatile materials (dashed lines). To the left of the vertical lines, the shielding effect works as the corotation radius is smaller than the sublimation radius. Overall, the material-shielding regime is represented by the upper left region of the plot separated by lines.