Abstract: An extensible boom is extended in an extension direction from a state of being rolled in a cylindrical form, the extension direction being one of short directions of the cylindrical form. Protruding portions and recessed portions are alternately formed at each of one end and another end in a long direction of the cylindrical form. The protruding portions at the one end are located opposite the recessed portions at the other end. The recessed portions at the one end are located opposite the protruding portions at the other end. When the extensible boom is extended along the extension direction, the protruding portions at the one end engage with the recessed portions at the other end, and the recessed portions at the one end engage with the protruding portions at the other end, such that a cylindrical shape is formed along the extension direction.

Abstract: A sputter target for forming a layer of a perpendicular recording medium by magnetron sputtering, wherein material composition of the sputter target is varied along a radius of the sputter target from a centre of the sputter target to an outer diameter of the sputter target.