A write operation method that is performed on a magnetic disk device, the magnetic disk device including a disk and a head, the head including at least one assist element and configured to write data to the disk, and the write operation method comprising:
- determining first and second assist energies to be applied by the at least one assist element to the disk during overwriting, based on an overwrite direction;
- and
- causing the first and second assist energies to be applied by the at least one assist element to the disk during the overwriting to affect a coercive force of the disk,
- wherein the first assist energy is different from the second assist energy.