Rotary actuator for disk drive

A rotary actuator for a disk drive having a base and at least one disk, comprising:

• an actuator arm assembly rotatably mounted on the base, said actuator arm assembly having one end portion for supporting a head and another end portion for supporting a moving coil;
• a magnetic circuit having a yoke fixed to the base and a main magnet fixed to said yoke, said magnetic circuit and said moving coil constituting a voice coil motor;
• and
• a retract magnet fixed to said actuator arm assembly so as to be opposed to said yoke of said magnetic circuit, wherein said yoke has a shape such that a radially extending gap is defined between said retract magnet and said yoke, and said radially extending gap gradually becomes smaller as said actuator arm assembly gradually approaches a lock position, whereby a magnetic attraction force between said retract magnet and said yoke gradually increases as said radially extending gap gradually becomes smaller;
• wherein when the disk drive is stopped in operation, said retract magnet magnetically reacts with said yoke to move said head to a given zone on the at least one disk and locks said actuator arm assembly at said lock position.