The detection and imaging of magnetic-field-induced strains via scanning probe microscopy enable us to observe magnetic domain structures. A perpendicular-recording head in a hard disk drive has been observed using this method to investigate the causes of head-induced data erasure. Domain structures of the main pole tip in a head that induces the erase-after-write phenomenon are observed, and we confirm the presence of remanent domains. The structures are not single domain but comprise multiple domains changing with the writing currents. The remanent magnetic fields causing the erase-after-write should be generated by the large magnetization near the domain walls. Copyright © 2014 John Wiley & Sons, Ltd.