Direct measurement of magnetodynamics in a perpendicular recording system

To characterize the magnetodynamic properties of a perpendicular recording system, consisting of a pole head, a recording layer, an exchangebreak layer, and a soft underlayer (SUL), we have built a test vehicle by depositing either the SUL, or the full medium stack on the air-bearing surface of the recording head. Using ultra-high-speed scanning Kerr microscopy, the intrinsic switching characteristics of the SUL and the impact of the recording layer on the former has been measured. One important feature found is the formation of vortices during reversal which are much larger than the pole area as well as evidence for spin wave excitation in the SUL. Both fast write current steps, and complex write current waveforms have been applied and significant differences of the magnetic responses are observed. Though the Kerr signal probes the temporal evolution of the SUL surface magnetization, it is possible to determine the onset of the recording layer switching by taking its magnetostatic coupling to the SUL into account. The magnetization state of the recording layer also impacts the switching speed of the SUL. The noise characteristics of the Kerr signal gives information about nonreproducible magnetization processes in the SUL.