Reverse dc erase medium noise analysis on exchange-coupling effect in coupled granular/continuous perpendicular recording media

Abstract

The role of intergranular exchange coupling was experimentally investigated in a coupled granular/continuous (CGC) perpendicular medium structure. By changing the number of Co/Pt bilayers in the continuous layer, the degree of exchange coupling can be systematically controlled. The switching field distribution (SFD) was roughly estimated from Kerr loops. The SFD became narrower for media with a thicker continuous layer. Using a head with a single-pole writer and an 80 nm gap giant magnetoresistance reader, reverse dc erase noise was measured as a function of the reverse dc erase current. The media showed a clear positive noise peak with an increase in reverse erase current. Narrowing of the SFD was reflected by narrowing of the noise peak width. However, the peak value of the medium’s noise also increased with an increase in the thickness of the continuous layer. Although exchange coupling increases the average magnetic cluster size in the demagnetization condition, CGC media with moderate exchange coupling showed no degradation of the signal to noise ratio compared to the base granular medium.