Magnetic theory of very small devices (invited)

A principal theme of this report is that the exchange-stiffness parameter replaces magnetic anisotropy as the principal core-material parameter (besides MS) governing the sensitivity of a read head when the cross-sectional dimensions of the core are less than 1 μm. A cylindrical magnetic tube within the core of a read head would provide micromagnetic advantages. Under certain conditions the unstable exchange energy stored in a magnetic vortex interacts with the stabilizing effect of self-demagnetization to amplify the stored flux by drawing fringing flux from the underlayer and shield. Reading characteristics which are valid, from the micromagnetic standpoint, down to storage-cell areas as small as (40 nm)2 are predicted. For sensitive reading, the core length must be near 100 (D/1 μm)2 μm, where D is the outer diameter of the tube.