A magnetic data recording system wherein the wherein adjacent track interference during writing is avoided by modulating the size of a write bubble on the magnetic media in response to a position error signal. If the position error signal indicates that the magnetic head is off-track, circuitry within the magnetic data recording system adjusts the size of the write bubble temporarily to prevent the write bubble from encroaching on a neighboring data track. This adjustment of the write bubble can be accomplished by adjusting power to the write head. Adjustment of the write bubble can also be achieved by adjusting power to a magnetic oscillator in a microwave assisted magnetic recording system (MAMR) or adjusting power to a heating element in a thermally assisted magnetic recording system.