Spindle motor having magnetic circuit for stator and rotor magnet, and storage disk drive having the same

A spindle motor for use in a 2.5 inch disk drive apparatus, the spindle motor comprising:

• a base portion;
• a stator arranged above the base portion;
• a rotor hub including a cover portion positioned above the stator, and a side wall portion arranged to extend downward from an outer edge of the cover portion;
• a rotor magnet positioned radially outward of the stator, and fixed to an inner circumferential surface of the side wall portion of the rotor hub;
• and
• a bearing mechanism arranged to support the rotor hub and the rotor magnet such that the rotor hub and the rotor magnet are rotatable with respect to the base portion and the stator;
• wherein
• a height of the rotor magnet as measured in an axial direction is in a range of about 2 mm to about 3 mm, both inclusive, and a height of a stator core of the stator as measured in the axial direction is in a range of about 50% to about 75%, both inclusive, of the height of the rotor magnet;
• and
• a torque constant of a torque produced between the stator and the rotor magnet is in a range of about 3 mNm/A to about 5 mNm/A, both inclusive.