irradiation onto the base plate 8 even during the sputtering operation by the first ion gun 1 by exciting the sputtering particles the state of the layer to be deposited onto the base plate 8 can be controlled so as to optimize the magnetic characteristic of the magnetic multilayer structure the desirable ion beam sputtering conditions to form a multilayer structure having a high saturation magnetic flux density and a high relative permeability were as follows ______________________________________target front surface fe purity 99 9 target back surface c purity 99 99 accelerating voltage of 1200 vthe first ion gunion current density of 1 2 ma cm sup 2the first ion gunaccelerating voltage of 200 vthe second ion gunion current density of 0 15 ma cm sup 2the second ion gunar pressure 2 5 u00d7 10 sup 2 patemperature of base plate 75 u00b0 c rotational speed of 100 r p m base plate______________________________________ the forming speeds of the fe layer and c layer were respectively independently measured under the above conditions the thickness of layer when forming a multilayer structure was controlled by the time in this case the layer forming speed of fe was 0 22 nm sec and that of c was 0 07 nm sec when forming a multilayer structure first the operation of the first ion gun was started and the presputtering processes of the fe and c targets were performed with a shutter not shown closed next the operation of the second ion gun was started thereafter the shutter was opened and formation of a multilayer structure was started in this example by rotating from the fe target to the c target and from the c target to.