Magnetization fluctuations and characteristic lengths for sputtered CoP/Cr thin-film media

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Abstract
Magnetization fluctuations of uniformly magnetized media have been measured in sputtered CoP thin films as a function of Cr underlayer thickness. Increasing underlayer thickness from 20 to 400 nm in nine steps yields decreasing magnetization fluctuation noise from 210 nm to about 25 nm, similar to the known decrease of transition noise. For virtually every disk, the noise power dependance on magnetization is well fit by the square of the magnetization versus current loop derivative, (dM/dI)2. Thus, the noise mechanism appears to be a modulation process over the entire series. Analysis of measured magnetization noise spectra yields approximate correlation lengths which decrease with increasing Cr underlayer thickness.