Magnetization reversal mechanism of soft magnetic underlayer pinned by antiferromagnetic layer

To realize high stray-field stability of a single-domain structure in the whole disk for a thick soft magnetic underlayer (SUL) pinned by an antiferromagnetic layer (AFM layer), inducing high exchange coupling field, Hex, is indispensable. However, Hex considerably decreases beyond theoretical expectation with increase in the SUL thickness. The local spin reversal along the film depth has been investigated in order to clarify the mechanism of the degradation of Hex in a thick SUL with an effective film thickness of 288 T nm. According to the results it was found that: (1) There exists an easily magnetized layer near the SUL surface side and a hardly magnetized layer at the bottom side of the SUL. (2) Magnetization reversal starts from the SUL surface by the domain-wall-displacement mode, and proceeds to the bottom of the SUL through rotation-magnetization mode. (3) In the present AFM/SUL interface design, to prevent the appearance of domain-wall-displacement mode, the effective SUL thickness should be kept lower than 200 T nm.