We have utilized antiferromagnetically coupled bilayer structures to magnetically tune hysteresis loop properties. A key element of this approach is the nonoverlapping switching field distribution of the two magnetic layers. This allows measurement of the magnetization reversal in the soft-magnetic layer (SL) at low fields without perturbing the magnetic state of the hard-magnetic layer (HL). The magnetization of HL can be changed by an appropriate high-field sequence, which also modifies the effective disorder level in SL due to the antiferromagnetic interlayer coupling. Variations of the SL hysteresis loop squareness by a factor of up to 50 are reported by utilizing this fully reversible tuning procedure.
Polarized small-angle neutron scattering has been used to measure the magnetic structure of a CoCrPt–SiOx thin-film data storage layer, contained within a writable perpendicular recording media, at granular (<10 nm) length scales. The magnetic contribution to the scattering is measured as the magnetization is reversed by an external field, providing unique spatial information on the switching process. A simple model of noninteracting nanomagnetic grains provides a good description of the data and an analysis of the grain-size dependent reversal provides strong evidence for an increase in magnetic anisotropy with grain diameter.
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