The limit of magnet remanence Br in moving coil actuators for disk drives

The expected future limit on a magnet´s residual flux density B_r due to decreased size in disk drive form factor is presented. Because, historically, the energy products of magnets have been increasing while the flux carrying capacity of steels has remained the same, one may expect a limit on further increase in B_r . For numerical illustration, the force exerted by the moving coil actuators in 2.5 in and 1.8 in disk drives is calculated as a function of B_r. These calculations show that one may expect no limit on B_r for any practical, future scenarios, but that the ratio of an increase in force for an increase in B _r diminishes