Head amplifier circuit with function for degaussing residual magnetism of recording head

A head amplifier circuit for use in a hard disk drive having a recording head which magnetically records data on a magnetic disk medium, comprising:

• a driver circuit configured to supply, in a data-recording mode, the recording head with a recording current corresponding to write data and serving as a first recording current, and to supply, in a degaussing mode, the recording head with a degaussing current serving as a second recording current, the second recording current being a recording current of a square wave which has a rising period and a falling period set longer than a rising period and a falling period of the first recording current;
• and a control circuit configured to control switching from the data-recording mode to the degaussing mode to control the driver circuit,
• wherein:
• write data of one sector recorded to the magnetic disk medium by the recording head includes user data and a postamble that forms a rear end of the write data;
• and the control circuit switches the driver circuit from the data-recording mode to the degaussing mode while part of the postamble is recorded on the magnetic disk medium, thereby controlling the recording of the remaining part of the postamble on the magnetic disk medium by the magnetic recording head, based on the degaussing current generated by the driver circuit.