Stable ultrahigh-density magnetooptical recordings using introduced lineardefects

The stability of data bits in magnetic recording media(1,2) at ultrahigh de nsities is compromised by the thermal 'flips'-magnetic spin reversals-of na no-sized spin domains(3), which erase the stored information. Media that ar e magnetized perpendicular to the plane of the film, such as ultrathin coba lt films or multilayered structures(4,5), are more stable against thermal s elf-erasure(2,6) than conventional memory devices. In this context, magneto optical memories seem particularly promising for ultrahigh-density recordin g on portable disks, and bit densities of similar to 100 Gbit inch(-2) (ref . 7) have been demonstrated using recent advances in the bit writing and re ading techniques(7-11). But the roughness and mobility of the magnetic doma in walls(12,13) prevents closer packing of the magnetic bits, and therefore presents a challenge to reaching even higher bit densities. Here we report that the strain imposed by a linear defect in a magnetic thin film can smo oth rough domain walls over regions hundreds of micrometres in size, and ha lt their motion. A scaling analysis of this process, based on the generic p hysics of disorder-controlled elastic lines(14-17), points to a simple way by which magnetic media might be prepared that can store data at densities in excess of 1 Tbit inch(-2).