A low coercivity material is known as being soft magnetically, while a high coercivity is considered to be hard. A low coercivity material can have it state changed by quite low magnetic fields. Early floppy disks could even be erased if you set a telephone on top of the disk and the phone rang. The magnetic field generated by the telephone bell caused this. The other property is retentivity - how much magnetism remains after the magnetizing force is removed.
Most people are familiar with the tapes in their audio cassettes.
While data tape and audio tapes are both forms of magnetic material their design is quite different. I'm going to try to explain the difference because that should make the entire process easier to understand. Remember that the shape of the particle is needle-like or bar shaped. In our magnetic 'paint' these particle are aligned in random directions. That means that some of the particle are going to pass under the head parallel to the head gap and since both the north and south poles pass under the head as the same time no current will be generated by the parallel particles.